Influence of Salt Intake on Association of Blood Uric Acid with Hypertension and Related Cardiovascular Risk

Association of hyperuricemia with risk of cardiovascular disease according to the number of risk factors within target range

BACKGROUND AND AIMS

Risk factor modification may decrease the risk of cardiovascular disease (CVD). Whether risk factor modification can mitigate the effect of hyperuricemia on CVD is unclear. This study aimed to investigate the risk of CVD among individuals with hyperuricemia, according to risk factors on target, compared with controls without hyperuricemia.

METHODS AND RESULTS

This prospective study included 91,722 participants free of CVD at baseline (2006-2007) of the Kailuan study. Individuals with hyperuricemia were categorized according to the number of seven selected risk factors within the guideline-recommended target range (nonsmoking, physical activity, healthy diet, guideline-recommended levels of body mass index, blood pressure, fasting blood glucose, and total cholesterol). During a median follow-up of 13.00 years, 671 out of 6740 individuals (9.96%) with hyperuricemia and 6301 out of 84,982 control subjects (7.41%) had incident CVD. Compared with control subjects without hyperuricemia, individuals with hyperuricemia who had 4 or 5 to 7 risk factors on target had no significant excess CVD risk, the hazard ratio (HR) (95% confidence internal [CI]) was 0.93 (0.79-1.10) and 0.88 (0.71-1.10), respectively. Among individuals with hyperuricemia, excess CVD risk decreased stepwise for a higher number of risk factors on target, the HR of CVD associated with per additional risk factor within target range was 0.82 (95% CI, 0.77-0.87). Similar results were yielded for CVD subtypes.

CONCLUSIONS

Among individuals with hyperuricemia, excess CVD risk decreased stepwise for a higher number of risk factors within target.

A study on the early metabolic effects of salt and fructose consumption: the protective role of water

Increasing serum osmolality has recently been linked with acute stress responses, which over time can lead to increased risk for obesity, hypertension, and other chronic diseases. Salt and fructose are two major stimuli that can induce acute changes in serum osmolality. Here we investigate the early metabolic effects of sodium and fructose consumption and determine whether the effects of sodium or fructose loading can be mitigated by blocking the change in osmolality with hydration. Forty-four healthy subjects without disease and medication were recruited into four groups. After overnight fasting, subjects in Group 1 drank 500 mL of salty soup, while those in Group 2 drank 500 mL of soup without salt for 15 min. Subjects in Group 3 drank 500 mL of 100% apple juice in 5 min, while subjects in Group 4 drank 500 mL of 100% apple juice and 500 mL of water in 5 min. Blood pressure (BP), plasma sodium, and glucose levels were measured every 15 min in the first 2 h. Serum and urine osmolarity, serum uric acid, cortisol, fibroblast growth factor 21 (FGF21), aldosterone, adrenocorticotropic hormone (ACTH) level, and plasma renin activity (PRA) were measured at the baseline and 2 h. Both acute intake of salt or fructose increased serum osmolality (maximum ∼4 mOsm/L peaking at 75 min) associated with a rise in systolic and diastolic BP, PRA, aldosterone, ACTH, cortisol, plasma glucose, uric acid, and FGF21. Salt tended to cause greater activation of the renin-angiotensin-system (RAS), while fructose caused a greater rise in glucose and FGF21. In both cases, hydration could prevent the osmolality and largely block the acute stress response. Acute changes in serum osmolality can induce remarkable activation of the ACTH-cortisol, RAS, glucose metabolism, and uric acid axis that is responsive to hydration. In addition to classic dehydration, salt, and fructose-containing sugars can activate these responses. Staying well hydrated may provide benefits despite exposure to sugar and salt. More studies are needed to investigate whether hydration can block the chronic effects of sugar and salt on disease.

An optimal dietary sodium chloride supplemental level of broiler chicks fed a corn-soybean meal diet from 1 to 21 days of age

Sodium chloride (NaCl) is usually added to diets to meet the Na and Cl requirements of broilers in the Chinese poultry industry, but the optimal dietary NaCl supplemental level was not well-established. The present study was conducted to estimate the optimal dietary NaCl supplemental level of broilers fed a corn-soybean meal diet from 1 to 21 days of age. A total of 490, 1-day-old Arbor Acres male broilers were fed a NaCl-unsupplemented corn-soybean meal basal diet (control) and the basal diet supplemented with 0.10, 0.20, 0.30, 0.40, 0.50 or 0.60% NaCl for 21 days. Regression analysis was conducted to evaluate the optimal dietary NaCl level using the best fitted broken-line or asymptotic models. As dietary supplemental NaCl levels increased, average daily gain (ADG), average daily feed intake (ADFI), blood partial pressure of CO₂, total CO₂, base excess and anion gap, blood concentrations of HCO₃, Na and Cl, serum Na concentration, jejunal villus height (VH) and tibia ash content increased linearly and quadratically (P < 0.05), while feed/gain ratio, relative weights of heart, liver and kidney, blood K concentration, serum concentrations of K, uric acid and glucose, and osmotic pressure decreased linearly and quadratically (P < 0.05). The estimates of optimal dietary NaCl levels were 0.20-0.22% based on the best fitted broken-line or asymptotic models (P < 0.0001) of ADG, ADFI and feed/gain ratio, and 0.08-0.24% based on the best fitted broken-line or asymptotic models (P < 0.0001) of blood gas indices, serum parameters, jejunal VH, tibia ash content and organ indices. These results suggested that the optimal dietary NaCl supplemental level would be 0.24% for broilers fed the corn-soybean meal diet from 1 to 21 days of age, which is lower than the current dietary NaCl supplemental level (0.30%) in the Chinese broiler production.

Dietary Sodium Intake and Health Indicators: A Systematic Review of Published Literature between January 2015 and December 2019

As the science surrounding population sodium reduction evolves, monitoring and evaluating new studies on intake and health can help increase our understanding of the associated benefits and risks. Here we describe a systematic review of recent studies on sodium intake and health, examine the risk of bias (ROB) of selected studies, and provide direction for future research. Seven online databases were searched monthly from January 2015 to December 2019. We selected human studies that met specified population, intervention, comparison, outcome, time, setting/study design (PICOTS) criteria and abstracted attributes related to the study population, design, intervention, exposure, and outcomes, and evaluated ROB for the subset of studies on sodium intake and cardiovascular disease risks or indicators. Of 41,601 abstracts reviewed, 231 studies were identified that met the PICOTS criteria and ROB was assessed for 54 studies. One hundred and fifty-seven (68%) studies were observational and 161 (70%) focused on the general population. Five types of sodium interventions and a variety of urinary and dietary measurement methods were used to establish and quantify sodium intake. Five observational studies used multiple 24-h urine collections to assess sodium intake. Evidence mainly focused on cardiovascular-related indicators (48%) but encompassed an assortment of outcomes. Studies varied in ROB domains and 87% of studies evaluated were missing information on ≥1 domains. Two or more studies on each of 12 outcomes (e.g., cognition) not previously included in systematic reviews and 9 new studies at low ROB suggest the need for ongoing or updated systematic reviews of evidence on sodium intake and health. Summarizing evidence from assessments on sodium and health outcomes was limited by the various methods used to measure sodium intake and outcomes, as well as lack of details related to study design and conduct. In line with research recommendations identified by the National Academies of Science, future research is needed to identify and standardize methods for measuring sodium intake.

Metabolites and Hypertension: Insights into Hypertension as a Metabolic Disorder: 2019 Harriet Dustan Award

For over 100 years, essential hypertension has been researched from different perspectives ranging from genetics, physiology, and immunology to more recent ones encompassing microbiology (microbiota) as a previously underappreciated field of study contributing to the cause of hypertension. Each field of study in isolation has uniquely contributed to a variety of underlying mechanisms of blood pressure regulation. Even so, clinical management of essential hypertension has remained somewhat static. We, therefore, asked if there are any converging lines of evidence from these individual fields that could be amenable for a better clinical prognosis. Accordingly, here we present converging evidence which support the view that metabolic dysfunction underlies essential hypertension.

The effect of uric acid and urinary sodium excretion on prehypertension: a nationwide population-based study

Background

This study examined the effect of serum uric acid (SUA) level and urinary sodium excretion on blood pressure as well as their combined effect on prehypertension in a Korean population.

Method

Data from the 7th Korea National Health and Nutrition Examination Survey for adults (≥ 19 years of age) were used. The participants were classified into two groups, normotension and prehypertension, according to the JNC-7 definition. Logistic regression was carried out and adjusted for traditionally regarded confounders of blood pressure. All analyses considered a complex sampling design. A multivariate analysis was performed on subgroups defined according to their SUA level and urinary sodium excretion.

Results

The 4200 participants were divided into normotension (n = 2646) and prehypertension (n = 1554) groups. In the univariate analysis, patient age, male sex, concurrent comorbidity (diabetes mellitus, cardiovascular disease, stroke, dyslipidemia, and chronic kidney disease), uric acid, and urinary sodium excretion were associated with prehypertension. After adjusting for baseline covariates, both the SUA level and urinary sodium excretion were significant predictors of incident prehypertension (SUA, per 1 mg/dL increase, odds ratio [OR] 1.216, 95% confidence interval [95% CI] 1.131–1.309; urinary sodium excretion, per 1 g/day increase, OR 1.067, 95% CI 1.019–1.117). Additionally, simultaneously higher tertiles of SUA and urinary sodium excretion resulted in higher ORs for prehypertension.

Conclusion

Increased SUA is a significant risk marker for the development of prehypertension in normotensives. Simultaneously high SUA and urinary sodium excretion amplified the effect on the development of prehypertension. Our findings suggest that lowering SUA levels and reducing sodium intake will contribute to preventing hypertension.

Association between urinary sodium excretion and uric acid, and its interaction on the risk of prehypertension among Chinese young adults

High uric acid (UA) level and high salt intake are reportedly associated with cardiovascular disease. This study investigated the association between UA and urinary sodium excretion, as well as its interaction on the risk of prehypertension. A total of 1869 participants without hypertension were recruited from a previously established cohort in Shaanxi Province, China. The participants were classified as normotensive or prehypertensive on the basis of their blood pressure. Increasing quartiles of sodium excretion were associated with high urinary UA/creatinine levels in prehypertensive participants. Estimated sodium excretion positively correlated with urinary UA/creatinine excretions in the prehypertensive group. In addition, the multivariate-adjusted odds ratios for prehypertension compared with normotension were 1.68 (1.27–2.22) for sodium excretion and 1.71 (1.21–2.42) for serum UA. Increasing sodium excretion and serum UA were associated with higher risk of prehypertension. Compared with the lowest quartiles, the highest sodium excretion and serum UA quartiles entailed 3.48 times greater risk of prehypertension. Sodium excretion is associated with urinary UA excretion in prehypertensive participants. The present study shows that high levels of salt intake and serum UA simultaneously are associated with a higher risk of prehypertension.

Effect of Salt Intake on Plasma and Urinary Uric Acid Levels in Chinese Adults: An Interventional Trial

Uric acid (UA) has been proposed as an important risk factor for cardiovascular and renal morbidity. We conducted an interventional trial to assess effects of altered salt intake on plasma and urine UA levels and the relationship between UA levels and salt sensitivity in humans. Ninety subjects (18–65 years old) were sequentially maintained on a normal diet for 3 days at baseline, a low-salt diet for 7 days (3.0 g/day, NaCl), and a high-salt diet for an additional 7 days (18.0 g/day of NaCl). Plasma UA levels significantly increased from baseline to low-salt diet and decreased from low-salt to high-salt diet. By contrast, daily urinary levels of UA significantly decreased from baseline to low-salt diet and increased from low-salt to high-salt diet. The 24 h urinary sodium excretions showed inverse correlation with plasma UA and positive correlation with urinary UA excretions. Additionally, salt-sensitive subjects presented significantly higher plasma UA changes in comparison to salt-resistant subjects, and a negative correlation was observed between degree of salt sensitivity and plasma UA difference. The present study indicates that variations in dietary salt intake affect plasma and urine UA levels, and plasma UA may be involved in pathophysiological process of salt sensitivity.

Comparison of sodium, potassium, calcium, magnesium, zinc, copper and iron concentrations of elements in 24-h urine and spot urine in hypertensive patients with healthy renal function

Sodium, potassium, calcium, magnesium, zinc, copper and iron are associated with the sequela of hypertension. The most reliable method for testing those elements is by collecting 24-h urine samples. However, this is cumbersome and collection of spot urine is more convenient in some circumstance. The aim of this study was to compare the concentrations of different elements in 24-h urine and spot urine.

METHODS

Data was collected from a sub-study of China Salt Substitute and Stroke Study. 240 participants were recruited randomly from 12 villages in two counties in Ningxia, China. Both spot and 24-h urine specimens were collected from each patient. Routine urine test was conducted, and concentration of elements was measured using microwave digestion and Inductively Coupled Plasma-Optical Emission Spectrometry. Partial correlation analysis and Spearman correlation analysis were used to investigate the concentration of different elements and the relationship between 24- h urine and spot urine.

RESULTS

A partial correlation in sodium, potassium, calcium, magnesium and iron was found between paired 24-h urine and spot urine samples except copper and zinc: 0.430, 0.426, 0.550, 0.221 and 0.191 respectively.

CONCLUSIONS

Spot urine can replace 24-h urine for estimating some of the elements in hypertensive patients with normal renal function.

Interaction of ACE genotype and salt intake on hypertension among Chinese Kazakhs: results from a population-based cross-sectional study

OBJECTIVES

To explore the effect of interaction between ACE genotype and salt intake on hypertension among Chinese Kazakhs, and to compare applications of interactions between logistic model and generalised partially linear tree-based regression (GPLTR) model.

DESIGN

Population-based cross-sectional study.

SETTING

Hong Dun, North Xinjiang, China.

PARTICIPANTS

Non-consanguineous Chinese Kazakh participants (n=916, 342 men and 574 women) aged ≥30 years.

MAIN OUTCOME MEASURES

Association between ACE genotype and hypertension, association between salt intake and hypertension, and interaction of ACE genotype and salt intake on hypertension in two models.

RESULTS

Associations between salt intake and hypertension were different in ACE genotype of II and ID+DD. Under the logistic models, main and interaction effects were not observed for men, but effects were present in opposite directions for women (main effect of ACE: OR=0.20, p=0.003; interaction effect: OR=1.07, p=0.027). Under the GPLTR model, Bayesian information criterion trees included both salt intake and ACE genotype as split variables. Individuals with a salt intake ≥19.5 g/day and ID+DD genotypes had a 3.99-fold (p=0.004) higher risk of hypertension compared with the II genotype for men, whereas salt intake <20.1 g/day and ID+DD genotypes had an OR=0.55 (p=0.014) compared with the II genotype for women.

CONCLUSIONS

An interaction of ACE genotype and salt intake on hypertension was observed among Chinese Kazakhs but in different ways according to sex. The GPLTR model appears to be more suitable for an exploration of interactions in complex diseases.

Prevalence, Awareness, Treatment, and Control of Hypertension among Kazakhs with high Salt Intake in Xinjiang, China: A Community-based Cross-sectional Study

Hypertension is a leading cause of death worldwide; data on hypertension among ethnic minorities in China are sparse. This study aimed to estimate hypertension prevalence, awareness, treatment, and control in a Kazakh population, and to assess the association between salt intake and the above measures. A cross-sectional survey was conducted among Kazakh adults (≥30 years old) in the town of Hongdun, Altay, Xinjiang. Survey procedures included a questionnaire, physical measurement, and laboratory tests. Of 1805 eligible individuals, 1668 (92.4%) were included in the analysis. After adjustment for gender, age, and occupation, prevalence of hypertension was 45.5%. The proportions with awareness, treatment, control, or medication-control were 61.0%, 28.8%, 2.9% and 10.1%, respectively. Higher prevalence was seen among nomads and farmers (50.7% and 44.6%, respectively). However, the proportions with treatment or control were lower than seen among urban citizens. Hypertension prevalence was higher in those with higher salt intake (p = 0.0008). In contrast, the proportions with awareness (p = 0.0389), treatment (p = 0.0010), control (p = 0.0503), and medication-control (p = 0.2012) reduced as salt intake increased. In conclusion, hypertension prevalence is high in this population, but the proportions with awareness, treatment, or control are sub-optimal. Public health interventions that improve hypertension prevention and control, particularly among nomads, is needed.

Opposing effects of sodium intake on uric acid and blood pressure and their causal implication

Reducing uric acid is hypothesized to lower blood pressure, although evidence is inconsistent. In this ancillary of the DASH-Sodium trial, we examined whether sodium-induced changes in serum uric acid (SUA) were associated with changes in blood pressure. One hundred and three adults with prestage or stage 1 hypertension were randomly assigned to receive either the DASH diet or a control diet (typical of the average American diet) and were fed each of the three sodium levels (low, medium, and high) for 30 days in random order. Body weight was kept constant. SUA was measured at baseline and following each feeding period. Participants were 55% women and 75% black. Mean age was 52 (SD, 10) years, and mean SUA at baseline was 5.0 (SD, 1.3) mg/dL. Increasing sodium intake from low to high reduced SUA (-0.4 mg/dL; P < .001) but increased systolic (4.3 mm Hg; P < .001) and diastolic blood pressure (2.3 mm Hg; P < .001). Furthermore, changes in SUA were independent of changes in systolic (P = .15) and diastolic (P = .63) blood pressure, regardless of baseline blood pressure, baseline SUA, and randomized diet, as well as sodium sensitivity. Although both SUA and blood pressure were influenced by sodium, a common environmental factor, their effects were in opposite directions and were unrelated to each other. These findings do not support a consistent causal relationship between SUA and BP.