Soft drink consumption during and following exercise in the heat elevates biomarkers of acute kidney injury

The work-recovery cycle of kidney strain and inflammation in sugarcane workers following repeat heat exposure at work and at home

PURPOSE

To examine heat exposure at work and home and the work-recovery cycle and temporal variation of kidney strain, muscle injury and inflammation biomarkers in sugarcane workers.

METHODS

20 male sugarcane workers (age: 33 ± 7 years) with a workplace Rest.Shade.Hydration (RSH) intervention were observed over 4 days, at the end (18 h post-shift recovery) and beginning of a work week (42 h post-shift recovery). Measures included work intensity (heart rate), gastro-intestinal temperature, estimated body core temperature (using heart rate), fluid consumption, pre- and post-work blood and urine samples, physical activity (accelerometery) away from work, plus ambient heat exposure at work and home.

RESULTS

On workdays, workers awakened at approx. 02:40 after 5 h sleep in ~ 30 °C. Across work shifts, daily average WBGT ranged from 26 to 29 °C (cooler than normal) and average workload intensity ranged from 55 to 58%HRmax. Workers reported consuming ~ 8 L of water and ~ 4 × 300 mL bags of electrolyte fluid each day. Serum creatinine, cystatin C and creatine phosphokinase markedly increased post-work and decreased during recovery; serum potassium did the opposite (all p < 0.01). Biomarker concentration changes were similar between recovery periods (18 h vs. 42 h; all p > 0.27). C-reactive protein was the highest at the end of the work week (p = 0.01).

CONCLUSION

Despite RSH intervention, cross-shift kidney strain was marked (recovering overnight) and systemic inflammation increased over the work week. Thus, biomonitoring of kidney function in occupational populations should be performed before a work shift at any point in the work week. This is essential knowledge for field studies and surveillance.

The Significance of Renal Impairment in Children with Eating Disorders

Background: Eating disorders have previously been associated with renal impairment. Low muscle mass reduces serum creatinine used for the calculation of the estimated glomerular filtration rate (eGFR), leading to overestimation of renal function. To solve this problem, the development of a tool to detect renal impairment in individual patients with a specific muscle mass is required to individualize risk assessment for further management. The objectives of our study were as follows: To investigate the percentage drop in creatinine (pdCr) during rehydration as a new indicator of renal dysfunction not dependent on muscle mass and to investigate a correlation between cardiovascular function and fluid management with renal function. Methods: In a 5-year retrospective cohort study of all consecutive children admitted because of an eating disorder, renal function expressed as eGFR on admission and as pdCr between admission and the lowest creatinine level was analysed in relation to cardiovascular parameters and fluid management. Results: We included 29 patients. The mean age was 13.4 years. A pdCr after admission was noted in 26/29 (89.7%). The eGFR was <90 in 15 (65%) and improved to >90 in 13/15 (86.6%). In patients with a fluid management plan, there was a median of 18.6% for those with pdCr and 6.4% (p = 0.02) for those without. Renal dysfunction was not related to cardiovascular parameters. Conclusions: The majority of patients with an eating disorder had renal impairment. PdCr was more sensitive in the detection of renal impairment in individual patients compared to eGFR.

The effect of consuming a sucrose-containing sports drink on acute kidney injury risk during a 4 h simulated occupational heat stress

Occupational heat stress increases acute kidney injury risk. Drinking a soft drink sweetened with high fructose corn syrup further elevates this acute kidney injury risk. However, the impact of sucrose, another fructose-containing sweetener, on acute kidney injury risk remains unexplored. We tested the hypothesis that drinking a sucrose-containing sports drink increases acute kidney injury risk when compared to drinking a sugar-free sports drink during 4 h of simulated occupational heat stress. Ten healthy adults consumed a sucrose-containing or sugar-free sport drink ad libitum during 4 h exposures to wet bulb globe temperatures of ∼28 °C. Thirty min of work and 30 min of rest were completed each hour. Work involved treadmill walking at a fixed rate of metabolic heat production (sucrose-containing: 6.0 ± 1.2 W/kg, sugar-free: 5.5 ± 0.9 W/kg, p = 0.267). The product of urinary insulin-like growth factor-binding protein 7 and tissue inhibitor of metalloproteinase-2, normalized to urine specific gravity ([IGFBP7·TIMP-2]USG), provided an acute kidney injury risk index. Mean core (intestinal: n = 13, rectal: n = 7) temperature (sucrose-containing: 37.5 ± 0.1 °C, sugar-free: 37.5 ± 0.3 °C; p = 0.914), peak core temperature (sucrose-containing: 37.8 ± 0.2 °C, sugar-free: 37.9 ± 0.3 °C; p = 0.398), and percent changes in body mass (sucrose-containing: -0.5 ± 0.4%, sugar-free: -0.3 ± 0.6%; p = 0.386) did not differ between groups. [IGFBP7∙TIMP-2]USG increased in both groups (time effect: p = 0.025) with no drink (p = 0.675) or interaction (p = 0.715) effects. Peak change [IGFBP7∙TIMP-2]USG did not differ between sucrose-containing (median 0.0116 [-0.0012, 0.1760] (ng/mL)2/1000) and sugar-free (median 0.0021 [0.0003, 0.2077] (ng/mL)2/1000; p = 0.796). Sucrose-containing sports drink consumption during simulated occupational heat stress does not modify acute kidney injury risk when compared to sugar free-sport drink consumption.

The mediation role of sleep on the relationship between drinks behavior and female androgenetic alopecia

Objectives

To investigate the relationship between drinks behavior and female androgenetic alopecia (AGA) and to clarify the mediating effect of sleep behavior on such relationship.

Methods

A total of 308 female AGA patients and 305 female normal controls were recruited from the hospital, and questionnaires including drinks behavior and sleep behavior were inquired among them. Blood sugar and blood lipids were detected. Then, the mediating effect of sleep behavior on the relationship between drinks behavior and AGA was analyzed.

Results

Female AGA patients presented a higher frequency of intake of sweetened tea drinks. It was found that occasional intake (1-2 times per week; ORadj = 2.130, 95% CI [1.495-3.033]) and frequent intake (3-6 time per week; ORadj = 2.054, 95% CI [1.015-4.157]) of sweetened tea drinks were associated with AGA. The daily sugar intake from soft drinks increased the risk of AGA (ORadj = 1.025, 95% CI [1.003-1.048]), and hyperglycemia was positively associated with alopecia (ORadj = 1.897, 95% CI [1.225-2.936]). In addition, bedtime after 12 pm significantly increased the risk of developing alopecia (ORadj = 2.609, 95% CI [1.020-6.676]). Interestingly, bedtime, instead of daily sugar intake from soft drinks, could mediate the relationship between sweetened tea drinks intake and alopecia.

Conclusions

Sweetened tea drinks consumption increases the risk of female AGA, which is mediated by bedtime.

Is mild dehydration a risk for progression of childhood chronic kidney disease?

Children with chronic kidney disease (CKD) can have an inherent vulnerability to dehydration. Younger children are unable to freely access water, and CKD aetiology and stage can associate with reduced kidney concentrating capacity, which can also impact risk. This article aims to review the risk factors and consequences of mild dehydration and underhydration in CKD, with a particular focus on evidence for risk of CKD progression. We discuss that assessment of dehydration in the CKD population is more challenging than in the healthy population, thus complicating the definition of adequate hydration and clinical research in this field. We review pathophysiologic studies that suggest mild dehydration and underhydration may cause hyperfiltration injury and impact renal function, with arginine vasopressin as a key mediator. Randomised controlled trials in adults have not shown an impact of improved hydration in CKD outcomes, but more vulnerable populations with baseline low fluid intake or poor kidney concentrating capacity need to be studied. There is little published data on the frequency of dehydration, and risk of complications, acute or chronic, in children with CKD. Despite conflicting evidence and the need for more research, we propose that paediatric CKD management should routinely include an assessment of individual dehydration risk along with a treatment plan, and we provide a framework that could be used in outpatient settings.

Impacts of age, type 2 diabetes, and hypertension on circulating neutrophil gelatinase-associated lipocalin and kidney injury molecule-1 after prolonged work in the heat in men

PURPOSE

Prolonged work in the heat increases the risk of acute kidney injury (AKI) in young men. Whether aging and age-associated chronic disease may exacerbate the risk of AKI remains unclear.

METHODS

We evaluated plasma neutrophil gelatinase-associated lipocalin (NGAL) and serum kidney injury molecule-1 (KIM1) before and after 180 min of moderate-intensity work (200 W/m2) in temperate (wet-bulb globe temperature [WBGT] 16 °C) and hot (32 °C) environments in healthy young (n = 13, 22 years) and older men (n = 12, 59 years), and older men with type 2 diabetes (T2D; n = 9, 60 years) or hypertension (HTN; n = 9, 60 years).

RESULTS

There were no changes in NGAL or KIM1 concentrations following prolonged work in temperate conditions in any group. Despite a similar work tolerance, the relative change in NGAL was greater in the older group when compared to the young group following exercise in the hot condition (mean difference + 82 ng/mL; p < 0.001). Baseline concentrations of KIM1 were ~ 22 pg/mL higher in the older relative to young group, increasing by ~ 10 pg/mL in each group after exercise in the heat (both p ≤ 0.03). Despite a reduced work tolerance in the heat in older men with T2D (120 ± 40 min) and HTN (108 ± 42 min), elevations in NGAL and KIM1 were similar to their healthy counterparts.

CONCLUSION

Age may be associated with greater renal stress following prolonged work in the heat. The similar biomarker responses in T2D and HTN compared to healthy older men, alongside reduced exercise tolerance in the heat, suggest these individuals may exhibit greater vulnerability to heat-induced AKI if work is prolonged.

Nourishing Physical Productivity and Performance On a Warming Planet - Challenges and Nutritional Strategies to Mitigate Exertional Heat Stress

PURPOSE OF REVIEW: Climate change is predicted to increase the frequency and severity of exposure to hot environments. This can impair health, physical performance, and productivity for active individuals in occupational and athletic settings. This review summarizes current knowledge and recent advancements in nutritional strategies to minimize the impact of exertional-heat stress (EHS). RECENT FINDINGS: Hydration strategies limiting body mass loss to < 3% during EHS are performance-beneficial in weight-supported activities, although evidence regarding smaller fluid deficits (< 2% body mass loss) and weight-dependent activities is less clear due to a lack of well-designed studies with adequate blinding. Sodium replacement requirements during EHS depends on both sweat losses and the extent of fluid replacement, with quantified sodium replacement only necessary once fluid replacement > 60-80% of losses. Ice ingestion lowers core temperature and may improve thermal comfort and performance outcomes when consumed before, but less so during activity. Prevention and management of gastrointestinal disturbances during EHS should focus on high carbohydrate but low FODMAP availability before and during exercise, frequent provision of carbohydrate and/or protein during exercise, adequate hydration, and body temperature regulation. Evidence for these approaches is lacking in occupational settings. Acute kidney injury is a potential concern resulting from inadequate fluid replacement during and post-EHS, and emerging evidence suggests that repeated exposures may increase the risk of developing chronic kidney disease. Nutritional strategies can help regulate hydration, body temperature, and gastrointestinal status during EHS. Doing so minimizes the impact of EHS on health and safety and optimizes productivity and performance outcomes on a warming planet.

Creatinine clearance is maintained in a range of wet-bulb globe temperatures and work-rest ratios during simulated occupational heat stress

We tested the hypothesis that compliance with the National Institute for Occupational Safety and Health (NIOSH) heat stress recommendations will prevent reductions in glomerular filtration rate (GFR) across a range of wet-bulb globe temperatures (WBGTs) and work-rest ratios at a fixed work intensity. We also tested the hypothesis that noncompliance would result in a reduction in GFR compared with a work-rest matched compliant trial. Twelve healthy adults completed five trials (four NIOSH compliant and one noncompliant) that consisted of 4 h of exposure to a range of WBGTs. Subjects walked on a treadmill (heat production: approximately 430 W) and work-rest ratios (work/h: 60, 45, 30, and 15 min) were prescribed as a function of WBGT (24°C, 26.5°C, 28.5°C, 30°C, and 36°C), and subjects drank a sport drink ad libitum. Peak core temperature (TC) and percentage change in body weight (%ΔBW) were measured. Creatinine clearance measured pre- and postexposure provided a primary marker of GFR. Peak TC did not differ among NIOSH-compliant trials (P = 0.065) but differed between compliant versus noncompliant trials (P < 0.001). %ΔBW did not differ among NIOSH-compliant trials (P = 0.131) or between compliant versus noncompliant trials (P = 0.185). Creatinine clearance did not change or differ among compliant trials (P ≥ 0.079). Creatinine clearance did not change or differ between compliant versus noncompliant trials (P ≥ 0.661). Compliance with the NIOSH recommendations maintained GFR. Surprisingly, despite a greater heat strain in a noncompliant trial, GFR was maintained highlighting the potential relative importance of hydration.NEW & NOTEWORTHY We highlight that glomerular filtration rate (GFR) is maintained during simulated occupational heat stress across a range of total work, work-rest ratios, and wet-bulb globe temperatures with ad libitum consumption of an electrolyte and sugar-containing sports drink. Compared with a work-rest matched compliant trial, noncompliance resulted in augmented heat strain but did not induce a reduction in GFR likely due to an increased relative fluid intake and robust fluid conservatory responses.

Sports drinks do not increase acute kidney injury risk in males during industrial work in the heat when euhydration is maintained, a randomized crossover trial

Industrial workers regularly perform physical labor under high heat stress, which may place them at risk for dehydration and acute kidney injury. Current guidelines recommend that workers should consume sports drinks to maintain euhydration during work shifts. However, the impact of fructose sweetened sports drinks on acute kidney injury risk is unknown. The purpose of this study was to investigate the effects of sports drink consumption on markers of acute kidney injury following simulated industrial work in the heat. Twenty males completed two matched 2 h simulated industrial work trial visits in a warm and humid environment (30 °C and 55% relative humidity). During and following the bout of simulated work, participants consumed either a commercially available sports drink or a noncaloric placebo. Urine and blood samples, collected pre-, post-, and 16 h post-work were assayed for markers of hydration (plasma/urine osmolality, and urine specific gravity) and acute kidney injury (KIM-1 and NGAL). There were no differences in physiological or perceptual responses to the bout of work (interaction p > 0.05 for all indices), and markers of hydration were similar between trials (interaction p > 0.05 for all indices). KIM-1 (Placebo: Δ Ln 1.18 ± 1.64; Sports drink: Δ Ln 1.49 ± 1.10 pg/mL; groupwide d = 0.89, p < 0.001) and NGAL (Placebo: Δ Ln 0.44 ± 1.11; Sports drink: Δ Ln 0.67 ± 1.22 pg/mL; groupwide d = 0.39, p = 0.03) were elevated pre- to post-work, but there were no differences between trials (interaction p > 0.05). These data provide no evidence that consumption of fructose sweetened sports drinks increases the risk of acute kidney injury during physical work in the heat.

Diagnostic accuracy of thermal, hydration, and heart rate assessments in discriminating positive acute kidney injury risk following physical work in the heat

Occupational heat stress increases the risk of acute kidney injury (AKI). This study presents a secondary analysis to generate novel hypotheses for future studies by investigating the diagnostic accuracy of thermal, hydration, and heart rate assessments in discriminating positive AKI risk following physical work in the heat in unacclimatized individuals. Unacclimatized participants (n = 13, 3 women, age: ∼23 years) completed four trials involving 2 h of exercise in a 39.7 ± 0.6 °C, 32 ± 3% relative humidity environment that differed by experimental manipulation of hyperthermia (i.e., cooling intervention) and dehydration (i.e., water drinking). Diagnostic accuracy was assessed via receiver operating characteristic curve analysis. Positive AKI risk was identified when the product of concentrations insulin-like growth factor binding protein 7 and tissue inhibitor of metalloproteinase-2 [IGFBP7∙TIMP-2] exceeded 0.3 (ng∙mL-1)2∙1000-1. Peak absolute core temperature had the acceptable discriminatory ability (AUC = 0.71, p = 0.009), but a relatively large variance (AUC 95% CI: 0.57-0.86). Mean body temperature, urine specific gravity, urine osmolality, peak heart rate, and the peak percent of both maximum heart rate and heart rate reserve had poor discrimination (AUC = 0.66-0.69, p ≤ 0.051). Mean skin temperature, percent change in body mass and plasma volume, and serum sodium and osmolality had no discrimination (p ≥ 0.072). A peak increase in mean skin temperature of >4.7 °C had a positive likelihood ratio of 11.0 which suggests clinical significance. These data suggest that the absolute value of peak core temperature and the increase in mean skin temperature may be valuable to pursue in future studies as a biomarker for AKI risk in unacclimatized workers.

Association between soft drinks intake and low glomerular filtration rate in Mexican adults: Results from RenMex

BACKGROUND & AIMS

To evaluate the association between soft drinks (SDs) consumption and estimated glomerular filtration rate (eGFR) in a Mexican adult population.

METHODS

We used data from the RenMex consortium (n = 2095) that included the Mexican Teachers Cohort Study (34-65 years), the Health Workers Cohort Study (18-90 years), and the Comitán Study (19-91 years). In this cross-sectional study, we assessed SDs consumption (cola and flavored soda) using a food frequency questionnaire (FFQ) and estimated eGFR using the CKD Epidemiology Collaboration equation. Quantile regression was used to assess the association between SDs consumption and eGFR with eGFR as a continuous variable. Multinomial logistic regression models were used for eGFR categories derived from quantile regression (mildly decreased eGFR, ≥72.9-87.9 mL/min/1.73 m2 and moderately decreased eGFR, <72.9 mL/min/1.73 m2).

RESULTS

Mean age of study participants was 47.2 years, 67.5% were women, and 12.2% had diabetes. eGFR was <60 mL/min/1.73 m2 in 3.7% of study participants. Mildly decreased eGFR was present in 14.8%, and moderately decreased eGFR was present in 10.1% of study participants. Quantile regression results showed that SDs consumption was associated with lower eGFR at the 10th, 25th, 50th and 75th percentile. Based on the final adjusted multinomial model, ≥7 servings/week was positively associated with moderately decreased eGFR relative to <1 serving/week (Relative Risk Ratio = 1.95; 95% CI: 1.07-3.57).

CONCLUSION

Our results suggest that higher SDs consumption is associated with lower eGFR. Encouraging healthy dietary choices should be part of the management and prevention of CKD.

Ambient heat and acute kidney injury: case-crossover analysis of 1 354 675 automated e-alert episodes linked to high-resolution climate data

BACKGROUND

As global temperatures continue to rise, the effects of ambient heat on acute kidney injury (AKI) are of growing concern. We used a novel nationwide electronic alert (e-alert) system to detect increases in AKI risk associated with high temperatures.

METHODS

We used a case-crossover design to link 1 354 675 AKI episodes occurring in England between April and September in years 2017-2021 to daily maximum temperature data at postcode sector level. AKI episode data were obtained from the UK Renal Registry. There were no further inclusion or exclusion criteria. Conditional logistic regression employing distributed lag non-linear models was used to assess odds of AKI episode on case days compared with day-of-week matched control days. Effects during heatwaves were also assessed using heat-episode analysis.

FINDINGS

There were strongly increased odds of AKI episode associated with high temperatures, with odds ratio (OR) 1·623 (95% CI 1·319-1·997) on a day of temperature 32°C compared with one of 17°C, the effects being strongest on a lag of 1 day. There was an OR of 1·020 (1·019-1·020) per 1°C increase in temperature above 17°C. The odds of a heat-related AKI episode were similar between AKI stages 1 and 2, but considerably lower for stage 3 events. A 7-day heatwave in July 2021 was associated with a 28·6% increase in AKI counts (95% CI 26·5-30·7).

INTERPRETATION

Heat-related AKI is a growing public health challenge. As even small changes in renal function can affect patient outcomes, susceptible individuals should be advised to take preventive measures whenever hot weather is forecast. Use of an e-alert system allows effects in milder cases that do not require secondary care to also be detected.

FUNDING

National Institute for Health and Care Research (NIHR).

Strategies to mitigate acute kidney injury risk during physical work in hot environments

Prolonged physical work in the heat can reduce renal function and increase the risk of acute kidney injury (AKI). This is concerning given that the latest climate change projections forecast a rise in global temperature as well as the frequency, intensity, and duration of heatwaves. This means that outdoor and indoor workers in the agriculture or construction industries will be exposed to higher heat stress in the years ahead. Several studies indicate a higher incidence of chronic kidney disease from nontraditional origins (CKDnt) in individuals exposed to high temperatures, intense physical work, and/or recurrent dehydration. It has been proposed that prolonged physical work in the heat accompanied by dehydration results in recurrent episodes of AKI that ultimately lead to permanent kidney damage and the development of CKDnt. Thus, there is a need to identify and test strategies that can alleviate AKI risk during physical work in the heat. The purpose of this review is to present strategies that might prevent and mitigate the risk of AKI induced by physical work in the heat.

Apple puree as a natural fructose source provides an effective alternative carbohydrate source for fuelling half-marathon running performance

Carbohydrate supplementation during endurance exercise is known to improve performance, but the effects of food-based approaches in running exercise are understudied. Therefore, this study investigated the performance and gastrointestinal (GI) effects of a carbohydrate supplement containing a natural fructose source compared with a highly processed fructose source in a combined glucose-fructose supplement, during a half-marathon. Eleven trained runners (9 males, 2 females; age 32 ± 8 y, 89:53 ± 13:28 min half-marathon personal record) completed a familiarisation (8 miles) and two experimental trials (13.1 miles) on an outdoor running course, with blood and urine samples collected before and after the run. Subjective GI measures were made throughout the run. Carbohydrate was provided as a natural fructose source in the form of apple puree (AP) or highly processed crystalline fructose (GF) in a 2:1 glucose-to-fructose ratio (additional required glucose was provided through maltodextrin). Half-marathon performance was not different between carbohydrate sources (AP 89:52 ± 09:33 min, GF 88:44 ± 10:09 min; P = 0.684). There were no interaction effects for GI comfort (P = 0.305) or other GI symptoms (P ≥ 0.211). There were no differences between carbohydrate sources in ad libitum fluid intake (AP 409 ± 206 mL; GF 294 ± 149 mL; P = 0.094) or any other urinary (P ≥ 0.724), blood-based (P ≥ 0.215) or subjective (P ≥ 0.421) measures. Apple puree as a natural fructose source was equivalent to crystalline fructose in supporting half-marathon running performance without increasing GI symptoms.HighlightsResearch examining food-first and food-based approaches to carbohydrate supplementation and endurance running performance are limited. Therefore, this study aimed to compare carbohydrate supplements either containing a natural or highly processed fructose source as part of a glucose-fructose supplement on half-marathon running performance and gastrointestinal comfort in trained runners.Running performance (apple puree 89:52 ± 09:33 min vs. crystalline fructose 88:44 ± 10:09 min), gastrointestinal comfort and symptoms were not different between the two fructose sources.Apple puree can be effectively used as a carbohydrate source to fuel half-marathon running performance.

The fructose survival hypothesis for obesity

The fructose survival hypothesis proposes that obesity and metabolic disorders may have developed from over-stimulation of an evolutionary-based biologic response (survival switch) that aims to protect animals in advance of crisis. The response is characterized by hunger, thirst, foraging, weight gain, fat accumulation, insulin resistance, systemic inflammation and increased blood pressure. The process is initiated by the ingestion of fructose or by stimulating endogenous fructose production via the polyol pathway. Unlike other nutrients, fructose reduces the active energy (adenosine triphosphate) in the cell, while blocking its regeneration from fat stores. This is mediated by intracellular uric acid, mitochondrial oxidative stress, the inhibition of AMP kinase and stimulation of vasopressin. Mitochondrial oxidative phosphorylation is suppressed, and glycolysis stimulated. While this response is aimed to be modest and short-lived, the response in humans is exaggerated due to gain of 'thrifty genes' coupled with a western diet rich in foods that contain or generate fructose. We propose excessive fructose metabolism not only explains obesity but the epidemics of diabetes, hypertension, non-alcoholic fatty liver disease, obesity-associated cancers, vascular and Alzheimer's dementia, and even ageing. Moreover, the hypothesis unites current hypotheses on obesity. Reducing activation and/or blocking this pathway and stimulating mitochondrial regeneration may benefit health-span. This article is part of a discussion meeting issue 'Causes of obesity: theories, conjectures and evidence (Part I)'.

Acute kidney injury biomarkers and hydration assessments following prolonged mild hypohydration in healthy young adults

The high prevalence of inadequate hydration (e.g., hypohydration and underhydration) is concerning given that extreme heat increases excess hospitalizations for fluid/electrolyte disorders and acute kidney injury (AKI). Inadequate hydration may also be related to renal and cardiometabolic disease development. This study tested the hypothesis that prolonged mild hypohydration increases the urinary AKI biomarker product of insulin-like growth factor-binding protein 7 and tissue inhibitor of metalloproteinase-2 ([IGFBP7·TIMP-2]) compared with euhydration. In addition, we determined the diagnostic accuracy and optimal cutoffs of hydration assessments for discriminating positive AKI risk ([IGFBP·TIMP-2] >0.3 (ng/mL)2/1,000). In a block-randomized crossover design, 22 healthy young adults (11 females and 11 males) completed 24 h of fluid deprivation (hypohydrated group) or 24 h of normal fluid consumption (euhydrated group) separated by ≥72 h. Urinary [IGFBP7·TIMP-2] and other AKI biomarkers were measured following the 24-h protocols. Diagnostic accuracy was assessed via receiver operating characteristic curve analysis. Urinary [IGFBP7·TIMP-2] [1.9 (95% confidence interval: 1.0-2.8) vs. 0.2 (95% confidence interval: 0.1-0.3) (ng/mL)2/1,000, P = 0.0011] was markedly increased in hypohydrated versus euhydrated groups. Urine osmolality (area under the curve: 0.91, P < 0.0001) and urine specific gravity (area under the curve: 0.89, P < 0.0001) had the highest overall performance for discriminating positive AKI risk. Optimal cutoffs with a positive likelihood ratio of 11.8 for both urine osmolality and specific gravity were 952 mosmol/kgH2O and 1.025 arbitrary units. In conclusion, prolonged mild hypohydration increased urinary [IGFBP7·TIMP-2] in males and females. Urinary [IGFBP7·TIMP-2] corrected to urine concentration was elevated in males only. Urine osmolality and urine specific gravity may have clinical utility for discriminating positive AKI risk following prolonged mild hypohydration.NEW & NOTEWORTHY This study found that prolonged mild hypohydration in healthy young adults increased the Food and Drug Administration approved acute kidney injury (AKI) biomarker urinary insulin-like growth factor-binding protein 7 and tissue inhibitor of metalloproteinase-2 [IGFBP7·TIMP-2]. Urine osmolality and specific gravity demonstrated an excellent ability to discriminate positive AKI risk. These findings emphasize the importance of hydration in protecting renal health and lend early support for hydration assessment as an accessible tool to assess AKI risk.

Fructose: A New Variable to Consider in SIADH and the Hyponatremia Associated With Long-Distance Running?

Fructose has recently been proposed to stimulate vasopressin secretion in humans. Fructose-induced vasopressin secretion is not only postulated to result from ingestion of fructose-containing drinks but may also occur from endogenous fructose production via activation of the polyol pathway. This raises the question of whether fructose might be involved in some cases of vasopressin-induced hyponatremia, especially in situations where the cause is not fully known such as in the syndrome of inappropriate secretion of diuretic hormone (SIADH) and exercise-associated hyponatremia, which has been observed in marathon runners. Here we discuss the new science of fructose and vasopressin, and how it may play a role in some of these conditions, as well as in the complications associated with rapid treatment (such as the osmotic demyelination syndrome). Studies to test the role of fructose could provide new pathophysiologic insights as well as novel potential treatment strategies for these common conditions.

Rapid weight loss can increase the risk of acute kidney injury in wrestlers

Objective

Restrictive diets, forced starvation or voluntary weight loss are attracting more and more attention from scientists. Overall trends show that about 80% of combat sports athletes use specific methods of reducing body mass. Rapid weight loss could be a risk factor for kidney-related adverse outcomes. This study aimed to examine the impact of high-intensity specific training combined with rapid weight loss in the first and without rapid weight loss in the second phases on body composition and biochemical markers of kidney function.

Methods

The study was conducted on 12 male wrestlers. Kidney function markers were measured, including blood urea nitrogen, serum creatinine, uric acid and serum Cystatin-C. Alterations in analysed markers were noted in both phases of the research.

Results

According to the data, a significant increase was noted in blood urea nitrogen (p=0.002), uric acid (p=0.000) and serum creatinine (p=0.006) during the first phase in comparison with the second phase. The levels of serum Cystatin-C were slightly elevated after both phases compared with the initial measurement.

Conclusion

It is evident that high-intensity specific training combined with rapid weight loss significantly affects the increase in kidney function markers compared with identical training without rapid weight loss. The findings in this study suggest that rapid body mass reduction is associated with an increased risk of acute kidney injury in wrestlers.

Environmental Exposures and Kidney Disease

Accumulating evidence underscores the large role played by the environment in the health of communities and individuals. We review the currently known contribution of environmental exposures and pollutants on kidney disease and its associated morbidity. We review air pollutants, such as particulate matter; water pollutants, such as trace elements, per- and polyfluoroalkyl substances, and pesticides; and extreme weather events and natural disasters. We also discuss gaps in the evidence that presently relies heavily on observational studies and animal models, and propose using recently developed analytic methods to help bridge the gaps. With the expected increase in the intensity and frequency of many environmental exposures in the decades to come, an improved understanding of their potential effect on kidney disease is crucial to mitigate potential morbidity and mortality.

Where do you live and what do you do? Two questions that might impact your kidney health

In many cases the social determinants of health need to be assessed through their interaction with environmental factors. This review looks at the impact of physical location and occupation of individuals on their kidney health. It examines the effect of living at high altitude on kidney function and the relationship between extreme cold or hot temperatures and the incidence of kidney injury. It reviews as well the many occupations that have been linked to kidney disease in high-income and low-and-middle-income countries. As a conclusion, this overview proposes preventive recommendations that could be individualized based on weather, altitude, socio-economic level of the country and occupation of the individual.

The impact of heat on kidney health: A PRISMA-compliant bibliometric analysis

BACKGROUND

Exposure to excessive heat can impact kidney health. Climate change is projected to aggravate this impact. An analysis of articles published between 1958 and 2021 was conducted to explore the progress of the research on this issue.

METHODS

This study included a bibliometric analysis wherein Web of Science was used to generate a list of all published articles related to the impact of heat on kidney health. Basic information about the articles, such as titles, authors' names, keywords, and citations, were recorded and analyzed.

RESULTS

A total of 226 published articles related to the impact of heat on kidney health were identified as of November 20, 2021. Most of these articles (93%) were published within the last decade. The United States was the most prominent country in terms of research productivity and collaboration. Researchers from the United States were well represented among the top 20 contributors of published articles on the study issue. The productivity of the top 20 authors varied between 6 and 32 articles each. A total of 25 common words used by the authors were identified. The most frequently used keywords were chronic kidney disease, heat stress, acute kidney injury, Mesoamerican nephropathy, and climate change. Keyword analysis revealed 3 distinct major research clusters in the existing scientific research on the impact of heat on kidney health: chronic kidney disease of unknown etiology, heat stress and renal physiology, and the effect of climate change on kidney health.

CONCLUSIONS

Research on heat-related kidney injury has witnessed rapid development in recent decades, motivated by the emergence of chronic kidney disease of unknown etiology and climate change. Developing countries in hot regions must increase their productivity in this research area through international collaboration and partnerships.

The effect of interval and continuous work on markers of acute kidney injury in a hot environment

PURPOSE

To examine the effect of high-intensity interval work (HIIW) and moderate-intensity continuous work (MICW) on markers of acute kidney injury (AKI) and kidney function in a hot environment.

METHODS

Nine males completed 2 h of work (2 × 60 min with 10 min passive rest) in a hot environment (40 °C and 15% relative humidity) as either HIIW [2 min at 80% peak oxygen consumption (VO₂peak) and 3 min at 30% VO₂peak] or MICW (matched for total work of HIIW). Blood and urine samples were collected immediately before (Pre), after (Post), 1 h (1 h Post), and 24 h after (24 h Post) the trials. Urine flow rate (UFR), creatinine clearance, insulin-like growth factor binding protein 7 (IGFBP7), urinary neutrophil gelatinase-associated lipocalin (uNGAL), and urinary kidney injury marker 1 (uKIM-1) were measured to assess kidney function and injury.

RESULTS

Log IGFBP7 (p < 0.01), log uNGAL (p < 0.01), and log uKIM-1 (p = 0.01) all displayed a main effect for time after both HIIW and MICW. IGFBP7 (p = 0.01) and uKIM-1 (p < 0.01), corrected for Uosm, were higher after HIIW compared to MICW at Post, while IGFBP7 was also higher 1 h Post after HIIW compared to MICW (p = 0.02). UFR significantly decreasing from Pre to Post (p < 0.01) and 1 h Post (p < 0.01), but no main effect for condition (p = 0.53).

CONCLUSION

Both HIIW and MICW in a hot environment caused an increase in biomarkers of kidney injury (IGFBP7, KIM-1, and NGAL), but HIIW may have a greater impact on biomarkers related to AKI.

Kidney injury risk during prolonged exposure to current and projected wet bulb temperatures occurring during extreme heat events in healthy young men

Wet bulb temperatures (Twet) during extreme heat events are commonly 31°C. Recent predictions indicate that Twet will approach or exceed 34°C. Epidemiological data indicate that exposure to extreme heat events increases kidney injury risk. We tested the hypothesis that kidney injury risk is elevated to a greater extent during prolonged exposure to Twet = 34°C compared with Twet = 31°C. Fifteen healthy men rested for 8 h in Twet = 31 (0)°C and Twet = 34 (0)°C. Insulin-like growth factor-binding protein 7 (IGFBP7), tissue inhibitor of metalloproteinase 2 (TIMP-2), and thioredoxin 1 (TRX-1) were measured from urine samples. The primary outcome was the product of IGFBP7 and TIMP-2 ([IGFBP7·TIMP-2]), which provided an index of kidney injury risk. Plasma interleukin-17a (IL-17a) was also measured. Data are presented at preexposure and after 8 h of exposure and as mean (SD) change from preexposure. The increase in [IGFBP7·TIMP-2] was markedly greater at 8 h in the 34°C [+26.9 (27.1) (ng/mL)2/1,000) compared with the 31°C [+6.2 (6.5) (ng/mL)2/1,000] trial (P < 0.01). Urine TRX-1, a marker of renal oxidative stress, was higher at 8 h in the 34°C [+77.6 (47.5) ng/min] compared with the 31°C [+16.2 (25.1) ng/min] trial (P < 0.01). Plasma IL-17a, an inflammatory marker, was elevated at 8 h in the 34°C [+199.3 (90.0) fg/dL; P < 0.01] compared with the 31°C [+9.0 (95.7) fg/dL] trial. Kidney injury risk is exacerbated during prolonged resting exposures to Twet experienced during future extreme heat events (34°C) compared with that experienced currently (31°C), likely because of oxidative stress and inflammatory processes.NEW AND NOTEWORTHY We have demonstrated that kidney injury risk is increased when men are exposed over an 8-h period to a wet bulb temperature of 31°C and exacerbated at a wet bulb temperature of 34°C. Importantly, these heat stress conditions parallel those that are encountered during current (31°C) and future (34°C) extreme heat events. The kidney injury biomarker analyses indicate both the proximal and distal tubules as the locations of potential renal injury and that the injury is likely due to oxidative stress and inflammation.

THIRSTY FOR FRUCTOSE: Arginine Vasopressin, Fructose, and the Pathogenesis of Metabolic and Renal Disease

We review the pathways by which arginine vasopressin (AVP) and hydration influence the sequelae of the metabolic syndrome induced by high fructose consumption. AVP and inadequate hydration have been shown to worsen the severity of two phenotypes associated with metabolic syndrome induced by high fructose intake-enhanced lipogenesis and insulin resistance. These findings have implications for those who frequently consume sweeteners such as high fructose corn syrup (HFCS). Patients with metabolic syndrome are at higher risk for microalbuminuria and/or chronic kidney disease; however, it is difficult to discriminate the detrimental renal effects of the metabolic syndrome from those of hypertension, impaired glucose metabolism, and obesity. It is not surprising the prevalence of chronic renal insufficiency is growing hand in hand with obesity, insulin resistance, and metabolic syndrome in those who consume large amounts of fructose. Higher AVP levels and low hydration status worsen the renal insufficiency found in patients with metabolic syndrome. This inter-relationship has public health consequences, especially among underserved populations who perform physical labor in environments that place them at risk for dehydration. MesoAmerican endemic nephropathy is a type of chronic kidney disease highly prevalent in hot ambient climates from southwest Mexico through Latin America. There is growing evidence that this public health crisis is being spurred by greater fructose consumption in the face of dehydration and increased dehydration-dependent vasopressin secretion. Work is needed at unraveling the mechanism(s) by which fructose consumption and increased AVP levels can worsen the renal disease associated with components of the metabolic syndrome.

Current Hydration Habits: The Disregarded Factor for the Development of Renal and Cardiometabolic Diseases

Improper hydration habits are commonly disregarded as a risk factor for the development of chronic diseases. Consuming an intake of water below recommendations (underhydration) in addition to the substitution of sugar-sweetened beverages (SSB) for water are habits deeply ingrained in several countries. This behavior is due to voluntary and involuntary dehydration; and because young children are exposed to SSB, the preference for a sweet taste is profoundly implanted in the brain. Underhydration and SSB intake lead to mild hyperosmolarity, which stimulates biologic processes, such as the stimulation of vasopressin and the polyol-fructose pathway, which restore osmolarity to normal but at the expense of the continued activation of these biological systems. Unfortunately, chronic activation of the vasopressin and polyol-fructose pathways has been shown to mediate many diseases, such as obesity, diabetes, metabolic syndrome, chronic kidney disease, and cardiovascular disease. It is therefore urgent that we encourage educational and promotional campaigns that promote the evaluation of personal hydration status, a greater intake of potable water, and a reduction or complete halting of the drinking of SSB.

High dietary salt intake increases urinary NGAL excretion and creatinine clearance in healthy young adults

In rodents and older patients with elevated blood pressure (BP), high dietary sodium increases excretion of biomarkers of kidney injury, but it is unclear whether this effect occurs in healthy young adults. The purpose of this study was to determine whether short-term high dietary salt increases urinary excretion of the kidney injury biomarkers neutrophil gelatinase-associated lipocalin (NGAL) and kidney injury molecule-1 (KIM-1) in healthy young adults. Twenty participants participated in a double-blind, placebo-controlled, randomized crossover study. For 10 days each, participants were asked to consume salt (3,900 mg sodium) or placebo capsules. We measured BP during each visit, obtained 24-h urine samples for measurements of electrolytes, NGAL, and KIM-1, and assessed creatinine clearance. Compared with placebo, salt loading increased daily urinary sodium excretion (placebo: 130.3 ± 62.4 mmol/24 h vs. salt: 287.2 ± 72.0 mmol/24 h, P < 0.01). There was no difference in mean arterial BP (placebo: 77 ± 7 mmHg vs. salt: 77 ± 6 mmHg, P = 0.83) between conditions. However, salt loading increased the urinary NGAL excretion rate (placebo: 59.8 ± 44.4 ng/min vs. salt: 80.8 ± 49.5 ng/min, P < 0.01) and increased creatinine clearance (placebo: 110.5 ± 32.9 mL/min vs. salt: 145.0 ± 24.9 mL/min, P < 0.01). Urinary KIM-1 excretion was not different between conditions. In conclusion, in healthy young adults 10 days of dietary salt loading increased creatinine clearance and increased urinary excretion of the kidney injury biomarker marker NGAL but not KIM-1.NEW & NOTEWORTHY In healthy young adults, 10 days of dietary salt loading increased creatinine clearance and increased urinary excretion of the kidney injury biomarker marker neutrophil gelatinase-associated lipocalin despite no change in resting blood pressure.

Impacts of Climate Change and Heat Stress on Farmworkers' Health: A Scoping Review

Due to the continuous rise of global temperatures and heatwaves worldwide as a result of climate change, concerns for the health and safety of working populations have increased. Workers in the food production chain, particularly farmworkers, are especially vulnerable to heat stress due to the strenuous nature of their work, which is performed primarily outdoors under poor working conditions. At the cross-section of climate change and farmworkers' health, a scoping review was undertaken to summarize the existing knowledge regarding the health impacts associated with climate change and heat stress, guide future research toward better understanding current and future climate change risks, and inform policies to protect the health and safety of agricultural workers. A systematic search of 5 electronic databases and gray literature websites was conducted to identify relevant literature published up until December 2021. A total of 9045 records were retrieved from the searches, of which 92 articles were included in the final review. The majority of the reviewed articles focused on heat-related illnesses (n = 57) and kidney diseases (n = 28). The risk factors identified in the reviewed studies included gender, dehydration, heat strain, wearing inappropriate clothing, workload, piece-rate payment, job decision latitude, and hot environmental conditions. On the other hand, various protective and preventive factors were identified including drinking water, changing work hours and schedule of activities, wearing appropriate clothing, reducing soda consumption, taking breaks in shaded or air-conditioned areas, and increasing electrolyte consumption in addition to improving access to medical care. This review also identified various factors that are unique to vulnerable agricultural populations, including migrant and child farmworkers. Our findings call for an urgent need to expand future research on vulnerable agricultural communities including migrant workers so as to develop effective policies and interventions that can protect these communities from the effects of heat stress.

Simultaneous assessment of motor and cognitive tasks reveals reductions in working memory performance following exercise in the heat

This study tested the hypothesis that, following exercise in the heat, motor task performance will be impaired when assessed simultaneously with a cognitive task. In a randomized, crossover and counterbalanced design, twelve healthy adults (23 ± 2 years, 5 women) completed four 10-minute exercise circuits involving upper and lower body exercise in a moderate (18.1 ± 1.7°C, 38 ± 10% relative humidity) and a hot (40.3 ± 1.1°C, 26 ± 5% relative humidity) environment. Experimental testing was completed in a temperate thermal environment before exercise (~25°C) and in either the moderate or hot environment following exercise. The 3 Back test (a test of working memory) was used as the cognitive task and postural sway was used as the motor task. Cognitive and motor task performance assessments were conducted both individually (solo) and simultaneously (dual). At the end of exercise, core temperature (by 0.4 ± 0.3°C, P < 0.001), heart rate (by 12 ± 18 bpm, P = 0.025), and mean skin temperature (by 7.6 ± 0.8°C, P < 0.001) were higher in the Hot trial compared to Moderate. During solo testing, postural sway increased from pre- to post-exercise in the Hot (P ≤ 0.028), but not the Moderate (P ≥ 0.261) trial. During dual testing, postural sway did not differ between trials (P ≥ 0.065) or over time (P ≥ 0.094). During solo testing, 3 Back performance did not differ between trials (P = 0.810) or over time (P = 0.707), but during dual testing 3 Back performance following exercise was reduced in the Hot compared to the Moderate trial (P = 0.028). Simultaneous assessment of motor and cognitive tasks reveals that motor performance is reduced following exercise in the heat. .

Cutaneous microvascular vasodilatory consequences of acute consumption of a caffeinated soft drink sweetened with high-fructose corn syrup

This study tested the hypotheses that compared to drinking water, consumption of a caffeinated soft drink sweetened with high-fructose corn syrup (HFCS) attenuates the cutaneous vasodilatory response to local skin heating without (Protocol 1) and following ischemia-reperfusion injury (Protocol 2). In a randomized, counterbalanced crossover design, 14 healthy adults (25 ± 3 year, 6 women) consumed 500 ml of water (water) or a caffeinated soft drink sweetened with HFCS (Mtn. Dew, DEW). Thirty minutes following beverage consumption local skin heating commenced on the right forearm (Protocol 1), while on the left forearm ischemia-reperfusion commenced with 20 min of ischemia followed by 20 min of reperfusion and then local skin heating (Protocol 2). Local skin heating involved 40 min of heating to 39℃ followed by 20 min of heating to 44℃. Skin blood flow (SkBf, laser Doppler) data were normalized to mean arterial pressure and are presented as a cutaneous vascular conductance (CVC) and as percentage of the CVC response during heating to 44℃ (%CVCmax ). Protocol 1: During local heating at 39℃, no differences were observed in CVC (water: 2.0 ± 0.6 PU/mmHg; DEW: 2.0 ± 0.8 PU/mmHg, p = 0.83) or %CVCmax (water: 59 ± 14%; DEW 60 ± 15%, p = 0.84) between trials. Protocol 2: During local skin heating at 39℃, no differences were observed in CVC (water: 1.7 ± 0.5 PU/mmHg; DEW: 1.5 ± 0.5 PU/mmHg, p = 0.33) or %CVCmax (water: 64 ± 15%; DEW 61 ± 15% p = 0.62) between trials. The cutaneous microvascular vasodilator response to local heating with or without prior ischemia-reperfusion injury is not affected by acute consumption of a caffeinated soft drink sweetened with HFCS.

Hypohydration produced by high-intensity intermittent running increases biomarkers of renal injury in males

Purpose

Whilst there is evidence to suggest that hypohydration caused by physical work in the heat increases renal injury, whether this is the case during exercise in temperate conditions remains unknown. This study investigated the effect of manipulating hydration status during high-intensity intermittent running on biomarkers of renal injury.

Methods

After familiarisation, 14 males (age: 33 ± 7 years; V̇O_2peak: 57.1 ± 8.6 ml/kg/min; mean ± SD) completed 2 trials in a randomised cross-over design, each involving 6, 15 min blocks of shuttle running (modified Loughborough Intermittent Shuttle Test protocol) in temperate conditions (22.3 ± 1.0 °C; 47.9 ± 12.9% relative humidity). During exercise, subjects consumed either a volume of water equal to 90% of sweat losses (EU) or 75 mL water (HYP). Body mass, blood and urine samples were taken pre-exercise (baseline/pre), 30 min post-exercise (post) and 24 h post-baseline (24 h).

Results

Post-exercise, body mass loss, serum osmolality and urine osmolality were greater in HYP than EU (P ≤ 0.024). Osmolality-corrected urinary kidney injury molecule-1 (uKIM-1) concentrations were increased post-exercise (P ≤ 0.048), with greater concentrations in HYP than EU (HYP: 2.76 [1.72–4.65] ng/mOsm; EU: 1.94 [1.1–2.54] ng/mOsm; P = 0.003; median [interquartile range]). Osmolality-corrected urinary neutrophil gelatinase-associated lipocalin (uNGAL) concentrations were increased post-exercise (P < 0.001), but there was no trial by time interaction effect (P = 0.073).

Conclusion

These results suggest that hypohydration produced by high-intensity intermittent running increases renal injury, compared to when euhydration is maintained, and that the site of this increased renal injury is at the proximal tubules.

Occupational heat exposure and the risk of chronic kidney disease of nontraditional origin in the United States

Occupational heat exposure is linked to the development of kidney injury and disease in individuals who frequently perform physically demanding work in the heat. For instance, in Central America, an epidemic of chronic kidney disease of nontraditional origin (CKDnt) is occurring among manual laborers, whereas potentially related epidemics have emerged in India and Sri Lanka. There is growing concern that workers in the United States suffer with CKDnt, but reports are limited. One of the leading hypotheses is that repetitive kidney injury caused by physical work in the heat can progress to CKDnt. Whether heat stress is the primary causal agent or accelerates existing underlying pathology remains contested. However, the current evidence supports that heat stress induces tubular kidney injury, which is worsened by higher core temperatures, dehydration, longer work durations, muscle damaging exercise, and consumption of beverages containing high levels of fructose. The purpose of this narrative review is to identify occupations that may place US workers at greater risk of kidney injury and CKDnt. Specifically, we reviewed the scientific literature to characterize the demographics, environmental conditions, physiological strain (i.e., core temperature increase, dehydration, heart rate), and work durations in sectors typically experiencing occupational heat exposure, including farming, wildland firefighting, landscaping, and utilities. Overall, the surprisingly limited available evidence characterizing occupational heat exposure in US workers supports the need for future investigations to understand this risk of CKDnt.

The Speed of Ingestion of a Sugary Beverage Has an Effect on the Acute Metabolic Response to Fructose

BACKGROUND

The consumption of sweetened beverages is associated with increased risk of metabolic syndrome, cardiovascular disease, and type 2 diabetes mellitus.

OBJECTIVE

We hypothesized that the metabolic effects of fructose in sugary beverages might be modulated by the speed of ingestion in addition to the overall amount.

DESIGN

Thirty healthy subjects free of any disease and medication were recruited into two groups. After overnight fasting, subjects in group 1 drank 500 mL of apple juice over an hour by drinking 125 mL every 15 min, while subjects in group 2 drank 500 mL of apple juice over 5 min. Blood samples were collected at time zero and 15, 30, 60, and 120 min after ingestion to be analyzed for serum glucose, insulin, homeostatic model assessment (HOMA-IR) score, fibroblast growth factor 21, copeptin, osmolarity, sodium, blood urea nitrogen (BUN), lactate, uric acid, and phosphate levels.

RESULTS

Serum glucose, insulin, HOMA-IR, fibroblast growth factor 21, copeptin, osmolarity, sodium, BUN, and lactate levels increased following apple juice ingestion. The increases were greater in the fast-drinking group, which were more significant after 15 min and 30 min compared to baseline. The changes in uric acid were not statistically different between the groups. Phosphate levels significantly increased only in the fast-drinking group.

CONCLUSION

Fast ingestion of 100% apple juice causes a significantly greater metabolic response, which may be associated with negative long-term outcomes. Our findings suggest that the rate of ingestion must be considered when evaluating the metabolic impacts of sweetened beverage consumption.

Arterial stiffness is not acutely modified by consumption of a caffeinated soft drink sweetened with high-fructose corn syrup in young healthy adults

We tested the hypothesis that ingestion of a caffeinated soft drink sweetened with high‐fructose corn syrup acutely increases arterial stiffness. In a randomized counterbalanced, crossover design, fourteen healthy adults (25 ± 3 years, 6 women) reported to the laboratory for two experimental visits where 500 ml of tap water (H₂O) or 500 ml of Mountain Dew® (a caffeinated soft drink sweetened with high‐fructose corn syrup (HFCS)) were consumed. Arterial stiffness (carotid‐to‐femoral pulse wave velocity (cfPWV)), peripheral and central blood pressures were measured pre‐consumption, 30 min post‐consumption, and 120 min post‐consumption. Prior to each measurement period, beat‐to‐beat hemodynamic measures were collected. Changes in heart rate, blood pressure, and cardiac output from pre‐consumption did not differ between trials at any timepoint (p ≥ 0.06). Moreover, changes in peripheral or central blood pressures from pre‐consumption did not differ between trials (p ≥ 0.84). Likewise, changes in cfPWV from pre‐consumption to 30 min post‐consumption (HFCS: 0.2 ± 0.3 m/s, H₂O: 0.0 ± 0.3 m/s, p = 0.34) and 120 min post‐consumption (HFCS: 0.3 ± 0.4 m/s, H₂O: 0.2 ± 0.3 m/s, p = 0.77) did not differ. Changes in aortic augmentation pressure, augmentation index, augmentation index corrected to a heart rate of 75 bpm, and reflection magnitude did not differ between conditions at 30 min post‐ (p ≥ 0.55) or 120 min post‐ (p ≥ 0.18) consumption. In healthy young adults, ingesting 500 ml of a commercially available caffeinated soft drink sweetened with high‐fructose corn syrup does not acutely change indices of arterial stiffness and wave reflection.

Effects of Exercise on Acute Kidney Injury Biomarkers and the Potential Influence of Fluid Intake

Acute kidney injury (AKI) incidence (diagnosed by changes in serum creatinine [Cr]) following prolonged endurance events has been reported to be anywhere from 4 to 85%, and hypohydration may contribute to this. Whilst an increase in serum Cr indicates impaired kidney function, this might be influenced by muscle damage. Therefore, the use of other AKI biomarkers which can detect renal tubular injury may be more appropriate. The long-term consequences of AKI are not well understood, but there are some potential concerns of an increased subsequent risk of chronic kidney disease (CKD). Therefore, this brief review explores the effects of exercise training/competition on novel AKI biomarkers and the potential influence of fluid intake. The increase in novel AKI biomarkers following prolonged endurance events suggests renal tubular injury. This is likely due to the long duration and relatively high exercise intensity, producing increased sympathetic tone, body temperature, hypohydration, and muscle damage. Whilst muscle damage appears to be an important factor in the pathophysiology of exercise-associated AKI, it may require coexisting hypohydration. Fluid intake seems to play a role in exercise-associated AKI, as maintaining euhydration with water ingestion during simulated physical work in the heat appears to attenuate rises in AKI biomarkers. The composition of fluid intake may also be important, as high-fructose drinks have been shown to exacerbate AKI biomarkers. However, it is yet to be seen if these findings are applicable to athletes performing strenuous exercise in a temperate environment. Additionally, further work should examine the effects of repeated bouts of strenuous exercise on novel AKI biomarkers.

Change in Exercise Performance and Markers of Acute Kidney Injury Following Heat Acclimation with Permissive Dehydration

Implementing permissive dehydration (DEH) during short-term heat acclimation (HA) may accelerate adaptations to the heat. However, HA with DEH may augment risk for acute kidney injury (AKI). This study investigated the effect of HA with permissive DEH on time-trial performance and markers of AKI. Fourteen moderately trained men (age and VO_2max = 25 ± 0.5 yr and 51.6 ± 1.8 mL·kg⁻¹·min⁻¹) were randomly assigned to DEH or euhydration (EUH). Time-trial performance and VO_2max were assessed in a temperate environment before and after 7 d of HA. Heat acclimation consisted of 90 min of cycling in an environmental chamber (40 °C, 35% RH). Neutrophil gelatinase-associated lipocalin (NGAL) and kidney injury molecule-1 (KIM-1) were assessed pre- and post-exercise on day 1 and day 7 of HA. Following HA, VO_2max did not change in either group (p = 0.099); however, time-trial performance significantly improved (3%, p < 0.01) with no difference between groups (p = 0.485). Compared to pre-exercise, NGAL was not significantly different following day 1 and 7 of HA (p = 0.113) with no difference between groups (p = 0.667). There was a significant increase in KIM-1 following day 1 and 7 of HA (p = 0.002) with no difference between groups (p = 0.307). Heat acclimation paired with permissive DEH does not amplify improvements in VO_2max or time-trial performance in a temperate environment versus EUH and does not increase markers of AKI.

Vasopressin mediates fructose-induced metabolic syndrome by activating the V1b receptor

Subjects with obesity frequently have elevated serum vasopressin levels, noted by measuring the stable analog, copeptin. Vasopressin acts primarily to reabsorb water via urinary concentration. However, fat is also a source of metabolic water, raising the possibility that vasopressin might have a role in fat accumulation. Fructose has also been reported to stimulate vasopressin. Here, we tested the hypothesis that fructose-induced metabolic syndrome is mediated by vasopressin. Orally administered fructose, glucose, or high-fructose corn syrup increased vasopressin (copeptin) concentrations and was mediated by fructokinase, an enzyme specific for fructose metabolism. Suppressing vasopressin with hydration both prevented and ameliorated fructose-induced metabolic syndrome. The vasopressin effects were mediated by the vasopressin 1b receptor (V1bR), as V1bR-KO mice were completely protected, whereas V1a-KO mice paradoxically showed worse metabolic syndrome. The mechanism is likely mediated in part by de novo expression of V1bR in the liver that amplifies fructokinase expression in response to fructose. Thus, our studies document a role for vasopressin in water conservation via the accumulation of fat as a source of metabolic water. Clinically, they also suggest that increased water intake may be a beneficial way to both prevent or treat metabolic syndrome.

Exercise intolerance in kidney diseases: physiological contributors and therapeutic strategies

Exertional fatigue, defined as the overwhelming and debilitating sense of sustained exhaustion that impacts the ability to perform activities of daily living, is highly prevalent in chronic kidney disease (CKD) and end-stage renal disease (ESRD). Subjective reports of exertional fatigue are paralleled by objective measurements of exercise intolerance throughout the spectrum of the disease. The prevalence of exercise intolerance is clinically noteworthy, as it leads to increased frailty, worsened quality of life, and an increased risk of mortality. The physiological underpinnings of exercise intolerance are multifaceted and still not fully understood. This review aims to provide a comprehensive outline of the potential physiological contributors, both central and peripheral, to kidney disease-related exercise intolerance and highlight current and prospective interventions to target this symptom. In this review, the CKD-related metabolic derangements, cardiac and pulmonary dysfunction, altered physiological responses to oxygen consumption, vascular derangements, and sarcopenia are discussed in the context of exercise intolerance. Lifestyle interventions to improve exertional fatigue, such as aerobic and resistance exercise training, are discussed, and the lack of dietary interventions to improve exercise tolerance is highlighted. Current and prospective pharmaceutical and nutraceutical strategies to improve exertional fatigue are also broached. An extensive understanding of the pathophysiological mechanisms of exercise intolerance will allow for the development of more targeted therapeutic approached to improve exertional fatigue and health-related quality of life in CKD and ESRD.

Restricted Water Intake and Hydration with Fructose-Containing Beverages during Infancy Predispose to Aggravate an Acute Renal Ischemic Insult in Adolescent Rats

We aimed to investigate the effects of chronic fluid restriction and hydration with a sweetened beverage (SB) in rats from weaning until adolescence, in a posterior acute kidney injury (AKI) event induced by ischemia-reperfusion (I/R). We followed 5 groups of weaning rats: control group (C); two groups with 22 h/day fluid restriction, a group hydrated for two hours with water (-W) and a group hydrated with SB; one group receiving SB ad libitum all day (+SB); and one group in which water consumption was increased using a gel diet. The rats that reached adolescence were submitted to I/R. Fluid restriction and/or SB hydration induced mild renal alterations that were significantly accentuated in the -SB group and resulted in worse outcomes after I/R-induced AKI that resulted in a catastrophic fall in creatinine clearance and diffuse acute tubular necrosis. In summary, low tap water intakes, as well as SB intake in infancy, prompt kidney worse outcomes in a later event of AKI during adolescence and both insults magnify kidney damage. Studies on hydration habits in children are recommended to disclose the potentially harmful effects that those behavioral patterns might carry to future renal health.

Kidney physiology and pathophysiology during heat stress and the modification by exercise, dehydration, heat acclimation and aging

The kidneys' integrative responses to heat stress aid thermoregulation, cardiovascular control, and water and electrolyte regulation. Recent evidence suggests the kidneys are at increased risk of pathological events during heat stress, namely acute kidney injury (AKI), and that this risk is compounded by dehydration and exercise. This heat stress related AKI is believed to contribute to the epidemic of chronic kidney disease (CKD) occurring in occupational settings. It is estimated that AKI and CKD affect upwards of 45 million individuals in the global workforce. Water and electrolyte disturbances and AKI, both of which are representative of kidney-related pathology, are the two leading causes of hospitalizations during heat waves in older adults. Structural and physiological alterations in aging kidneys likely contribute to this increased risk. With this background, this comprehensive narrative review will provide the first aggregation of research into the integrative physiological response of the kidneys to heat stress. While the focus of this review is on the human kidneys, we will utilize both human and animal data to describe these responses to passive and exercise heat stress, and how they are altered with heat acclimation. Additionally, we will discuss recent studies that indicate an increased risk of AKI due to exercise in the heat. Lastly, we will introduce the emerging public health crisis of older adults during extreme heat events and how the aging kidneys may be more susceptible to injury during heat stress.

Changes in Novel AKI Biomarkers after Exercise. A Systematic Review

More than 100 substances have been identified as biomarkers of acute kidney injury. These markers can help to diagnose acute kidney injury (AKI) in its early phase, when the creatinine level is not increased. The two markers most frequently studied in plasma and serum are cystatin C and neutrophil gelatinase-associated lipocalin (NGAL). The former is a marker of kidney function and the latter is a marker of kidney damage. Some other promising serum markers, such as osteopontin and netrin-1, have also been proposed and studied. The list of promising urinary markers is much longer and includes cystatin C, NGAL, kidney injury molecule-1 (KIM-1), liver-type fatty-acid-binding protein (L-FABP), interleukin 18, insulin-like growth factor binding protein 7 (IGFBP-7), tissue inhibitor of metalloproteinases-2 (TIMP-2) and many others. Although these markers are increased in urine for no longer than a few hours after nephrotoxic agent action, they are not widely used in clinical practice. Only combined IGFBP-7/TIMP-2 measurement was approved in some countries as a marker of AKI. Several studies have shown that the levels of urinary AKI biomarkers are increased after physical exercise. This systematic review focuses on studies concerning changes in new AKI biomarkers in healthy adults after single exercise. Twenty-seven papers were identified and analyzed in this review. The interpretation of results from different studies was difficult because of the variety of study groups, designs and methodology. The most convincing data concern cystatin C. There is evidence that cystatin C is a better indicator of glomerular filtration rate (GFR) in athletes after exercise than creatinine and also at rest in athletes with a lean mass lower or higher than average. Serum and plasma NGAL are increased after prolonged exercise, but the level also depends on inflammation and hypoxia; therefore, it seems that in physical exercise, it is too sensitive for AKI diagnosis. It may, however, help to diagnose subclinical kidney injury, e.g., in rhabdomyolysis. Urinary biomarkers are increased after many types of exercise. Increases in NGAL, KIM-1, cystatin-C, L-FABP and interleukin 18 are common, but the levels of most urinary AKI biomarkers decrease rapidly after exercise. The importance of this short-term increase in AKI biomarkers after exercise is doubtful. It is not clear if it is a sign of mild kidney injury or physiological metabolic adaptation to exercise.

Hydration Choices, Sugary Beverages, and Kidney Injury in Agricultural Workers in California

PURPOSE

Agricultural workers working in high ambient temperatures are at risk for acute kidney injury. Despite recommendations to maintain hydration, workers likely do not drink enough to protect their renal function. Additionally, new research suggests that rehydration with sugary beverages adds additional risk to kidneys already stressed by high heat and workload. We assessed hydration choices during a work shift and tested associations of rehydration using sugary beverages with acute kidney injury.

METHODS

We recruited a convenience sample of workers on farms over two summers. We estimated acute kidney injury via pre- and post-shift serum creatinine readings from capillary blood samples. We used self-reported measures of the volume and type of fluids workers consumed during their shifts. We also measured changes in core body temperature, ambient temperature, and workload. We used logistic regression to estimate associations of sugary drinks with acute kidney injury, while controlling for physiologic and occupational variables.

FINDINGS

In our sample of 445 participants, we found that men drink more than women do overall, including more than a liter of water than women (2.9 L compared to 1.9 L, respectively). The total volume workers drank was associated with increased odds of acute kidney injury (adjusted odds ratio 1.47, 95% confidence interval 1.09-1.99). We found no association of sugary drinks with acute kidney injury.

CONCLUSIONS

These findings provide important information about what men and women use to hydrate during the work day and suggest that they do not drink enough to maintain adequate hydration. Increased fluid intake during the work day may be a result of vigorous workload, which could explain the increased risk for acute kidney injury. Nurses play an important role in educating agricultural workers about the importance of maintaining hydration at work.

CLINICAL RELEVANCE

This study advances current knowledge of occupational risk factors for acute kidney injury in agricultural workers. Nurses may be the only point of care for this vulnerable population and are therefore in a unique position to educate on the importance of proper hydration during work.

Pathophysiological Mechanisms by which Heat Stress Potentially Induces Kidney Inflammation and Chronic Kidney Disease in Sugarcane Workers

BACKGROUND

Chronic kidney disease of non-traditional origin (CKDnt) is common among Mesoamerican sugarcane workers. Recurrent heat stress and dehydration is a leading hypothesis. Evidence indicate a key role of inflammation.

METHODS

Starting in sports and heat pathophysiology literature, we develop a theoretical framework of how strenuous work in heat could induce kidney inflammation. We describe the release of pro-inflammatory substances from a leaky gut and/or injured muscle, alone or in combination with tubular fructose and uric acid, aggravation by reduced renal blood flow and increased tubular metabolic demands. Then, we analyze longitudinal data from >800 sugarcane cutters followed across harvest and review the CKDnt literature to assess empirical support of the theoretical framework.

RESULTS

Inflammation (CRP elevation and fever) and hyperuricemia was tightly linked to kidney injury. Rehydrating with sugary liquids and NSAID intake increased the risk of kidney injury, whereas electrolyte solution consumption was protective. Hypokalemia and hypomagnesemia were associated with kidney injury.

DISCUSSION

Heat stress, muscle injury, reduced renal blood flow and fructose metabolism may induce kidney inflammation, the successful resolution of which may be impaired by daily repeating pro-inflammatory triggers. We outline further descriptive, experimental and intervention studies addressing the factors identified in this study.

Sugar-Induced Obesity and Insulin Resistance Are Uncoupled from Shortened Survival in Drosophila

High-sugar diets cause thirst, obesity, and metabolic dysregulation, leading to diseases including type 2 diabetes and shortened lifespan. However, the impact of obesity and water imbalance on health and survival is complex and difficult to disentangle. Here, we show that high sugar induces dehydration in adult Drosophila, and water supplementation fully rescues their lifespan. Conversely, the metabolic defects are water-independent, showing uncoupling between sugar-induced obesity and insulin resistance with reduced survival in vivo. High-sugar diets promote accumulation of uric acid, an end-product of purine catabolism, and the formation of renal stones, a process aggravated by dehydration and physiological acidification. Importantly, regulating uric acid production impacts on lifespan in a water-dependent manner. Furthermore, metabolomics analysis in a human cohort reveals that dietary sugar intake strongly predicts circulating purine levels. Our model explains the pathophysiology of high-sugar diets independently of obesity and insulin resistance and highlights purine metabolism as a pro-longevity target.

High-fructose corn syrup-sweetened soft drink consumption increases vascular resistance in the kidneys at rest and during sympathetic activation

We first tested the hypothesis that consuming a high-fructose corn syrup (HFCS)-sweetened soft drink augments kidney vasoconstriction to sympathetic stimulation compared with water (study 1). In a second study, we examined the mechanisms underlying these observations (study 2). In study 1, 13 healthy adults completed a cold pressor test, a sympathoexcitatory maneuver, before (preconsumption) and 30 min after drinking 500 mL of decarbonated HFCS-sweetened soft drink or water (postconsumption). In study 2, venous blood samples were obtained in 12 healthy adults before and 30 min after consumption of 500 mL water or soft drinks matched for caffeine content and taste, which were either artificially sweetened (Diet trial), sucrose-sweetened (Sucrose trial), or sweetened with HFCS (HFCS trial). In both study 1 and study 2, vascular resistance was calculated as mean arterial pressure divided by blood velocity, which was measured via Doppler ultrasound in renal and segmental arteries. In study 1, HFCS consumption increased vascular resistance in the segmental artery at rest (by 0.5 ± 0.6 mmHg·cm^-1·s^-1, P = 0.01) and during the cold pressor test (average change: 0.5 ± 1.0 mmHg·cm^-1·s^-1, main effect: P = 0.05). In study 2, segmental artery vascular resistance increased in the HFCS trial (by 0.8 ± 0.7 mmHg·cm^-1·s^-1, P = 0.02) but not in the other trials. Increases in serum uric acid were greater in the HFCS trial (0.3 ± 0.4 mg/dL, P ≤ 0.04) compared with the Water and Diet trials, and serum copeptin increased in the HFCS trial (by 0.8 ± 1.0 pmol/L, P = 0.06). These findings indicate that HFCS acutely increases vascular resistance in the kidneys, independent of caffeine content and beverage osmolality, which likely occurs via simultaneous elevations in circulating uric acid and vasopressin.

Association of Copeptin, a Surrogate Marker of Arginine Vasopressin, with Decreased Kidney Function in Sugarcane Workers in Guatemala

BACKGROUND

Vasopressin is elevated in response to heat and dehydration and has been postulated to have a role in the chronic kidney disease of unknown origin being observed in Central America. The aims of this study were to examine whether the vasopressin pathway, as measured by copeptin, is associated with the presence of kidney dysfunction, and to examine whether higher fluid intake is associated with lower circulating copeptin and thereby preserves kidney health among sugarcane workers exposed to hot conditions.

METHODS

Utilizing a longitudinal study of 105 workers in Guatemala, we examined relationships between hydration indices, plasma copeptin concentrations, and kidney function markers at 3 times during the 6-month harvest. We also examined whether baseline copeptin concentrations increased the odds of developing an estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m2.

RESULTS

Copeptin concentrations were positively associated with serum creatinine (β 1.41, 95% CI 0.88-2.03) and negatively associated with eGFR (β -1.07, 95% CI -1.43 to -0.70). In addition, as workers improved their hydration (measured by increases in fluid balance), copeptin concentrations were reduced, and this reduction was associated with an improvement in kidney function.

CONCLUSIONS

Results suggest that copeptin should be studied as a potential prognostic biomarker.

Fructose metabolism as a common evolutionary pathway of survival associated with climate change, food shortage and droughts

Mass extinctions occur frequently in natural history. While studies of animals that became extinct can be informative, it is the survivors that provide clues for mechanisms of adaptation when conditions are adverse. Here, we describe a survival pathway used by many species as a means for providing adequate fuel and water, while also providing protection from a decrease in oxygen availability. Fructose, whether supplied in the diet (primarily fruits and honey), or endogenously (via activation of the polyol pathway), preferentially shifts the organism towards the storing of fuel (fat, glycogen) that can be used to provide energy and water at a later date. Fructose causes sodium retention and raises blood pressure and likely helped survival in the setting of dehydration or salt deprivation. By shifting energy production from the mitochondria to glycolysis, fructose reduced oxygen demands to aid survival in situations where oxygen availability is low. The actions of fructose are driven in part by vasopressin and the generation of uric acid. Twice in history, mutations occurred during periods of mass extinction that enhanced the activity of fructose to generate fat, with the first being a mutation in vitamin C metabolism during the Cretaceous-Paleogene extinction (65 million years ago) and the second being a mutation in uricase that occurred during the Middle Miocene disruption (12-14 million years ago). Today, the excessive intake of fructose due to the availability of refined sugar and high-fructose corn syrup is driving 'burden of life style' diseases, including obesity, diabetes and high blood pressure.

Both hyperthermia and dehydration during physical work in the heat contribute to the risk of acute kidney injury

Occupational heat stress increases the risk of acute kidney injury (AKI) and kidney disease. This study tested the hypothesis that attenuating the magnitude of hyperthermia (i.e., increase in core temperature) and/or dehydration during prolonged physical work in the heat attenuates increases in AKI biomarkers. Thirteen healthy adults (3 women, 23 ± 2 yr) exercised for 2 h in a 39.7 ± 0.6°C, 32 ± 3% relative-humidity environmental chamber. In four trials, subjects received water to remain euhydrated (Water), continuous upper-body cooling (Cooling), a combination of both (Water + Cooling), or no intervention (Control). The magnitude of hyperthermia (increased core temperature of 1.9 ± 0.3°C; P < 0.01) and dehydration (percent loss of body mass of -2.4 ± 0.5%; P < 0.01) were greatest in the Control group. There were greater increases in the urinary biomarkers of AKI in the Control trial: albumin (increase of 13 ± 11 μg/mL; P ≤ 0.05 compared with other trials), neutrophil gelatinase-associated lipocalin (NGAL) (increase of 16 ± 14 ng/dL, P ≤ 0.05 compared with Cooling and Water + Cooling groups), and insulin-like growth factor-binding protein 7 (IGFBP7) (increase of 227 ± 190 ng/mL; P ≤ 0.05 compared with other trials). Increases in IGFBP7 in the Control trial persisted after correcting for urine production/concentration. There were no differences in the AKI biomarker tissue inhibitor of metalloproteinase 2 (TIMP-2) between trials (P ≥ 0.11). Our findings indicate that the risk of AKI is highest with greater magnitudes of hyperthermia and dehydration during physical work in the heat. Additionally, the differential findings between IGFBP7 (preferentially secreted in proximal tubules) and TIMP-2 (distal tubules) suggest the proximal tubules as the location of potential renal injury.NEW & NOTEWORTHY We demonstrate that the risk for acute kidney injury (AKI) is higher in humans with greater magnitudes of hyperthermia and dehydration during physical work in the heat and that alleviating the hyperthermia and/or limiting dehydration equally reduce the risk of AKI. The biomarker panel employed in this study suggests the proximal tubules as the location of potential renal injury.