Longitudinal relationships between diet-dependent renal acid load and blood pressure development in healthy children

Dietary Acid Load and Human Health: A Systematic Review and Meta-analysis of Observational Studies

CONTEXT

Dietary acid load (DAL) plays an important role in different aspects of human health.

OBJECTIVE

The aim of this meta-analysis was to systematically synthesize the observational evidence reporting on the associations between the DAL (represented by a potential renal acid load [PRAL] and net endogenous acid production [NEAP]) and a range of health outcomes.

DATA SOURCES

A systematic search of Medline (via PubMed), EMBASE, Scopus, and Web of Science was performed to identify eligible studies.

DATA EXTRACTION

Study screening and risk-of-bias assessment were conducted by 2 independent reviewers.

DATA ANALYSIS

The credibility of each outcome was graded based on predefined criteria: pooled effect size with corresponding 95% CI, 95% prediction interval, heterogeneity, small-study effect, and excess significance bias. In total, 118 observational studies (case-control [n = 22], cross-sectional [n = 65], and cohort [n = 31]) on 38 outcomes were included, incorporating a total population of 1 014 081 participants. Overall, 21/37 and 20/38 of the outcomes reported statistically significant effect sizes for PRAL and NEAP, respectively. The credibility of the evidence for PRAL was rated convincing (class I) for type 2 diabetes (T2D), and as highly suggestive evidence (class II) for overall cancer and systolic blood pressure. By assessing the credibility of the evidence for NEAP, T2D and overall cancer presented convincing evidence (class I) and breast cancer presented highly suggestive evidence (class II). The remaining outcomes presented class III (suggestive) or lower evidence (weak or no association).

CONCLUSION

The higher acid-forming potential of diet was associated with a higher risk of T2D and overall cancer. Since this meta-analysis included observational studies and some of the associations were graded as weak, caution should be exercised in interpreting these associations. Further cohort studies are required with consideration of other factors that can cause biases.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO registration no. CRD42022336050.

Effects of higher dietary acid load: a narrative review with special emphasis in children

Metabolic effects of high diet acid load (DAL) have been studied for years in adults, although only recently in children. Contemporary diets, especially those of Western societies, owe their acidogenic effect to high animal-origin protein content and low contribution of base-forming elements, such as fruits and vegetables. This imbalance, where dietary acid precursors exceed the body's buffering capacity, results in an acid-retaining state known by terms such as "eubicarbonatemic metabolic acidosis," "low-grade metabolic acidosis," "subclinical acidosis," or "acid stress". Its consequences have been linked to chronic systemic inflammation, contributing to various noncommunicable diseases traditionally considered more common in adulthood, but now have been recognized to originate at much earlier ages. In children, effects of high DAL are not limited to growth impairment caused by alterations of bone and muscle metabolism, but also represent a risk factor for conditions such as obesity, insulin resistance, diabetes, hypertension, urolithiasis, and chronic kidney disease (CKD). The possibility that high DAL may be a cause of chronic acid-retaining states in children with growth impairment should alert pediatricians and pediatric nephrologists, since its causes have been attributed traditionally to inborn errors of metabolism and renal pathologies such as CKD and renal tubular acidosis. The interplay between DAL, overall diet quality, and its cascading effects on children's health necessitates comprehensive nutritional assessments and interventions. This narrative review explores the clinical relevance of diet-induced acid retention in children and highlights the potential for prevention through dietary modifications, particularly by increasing fruit and vegetable intake alongside appropriate protein consumption.

Phosphorus Intake and Potential Dietary Influences Examined via 24-Hour Urinary Biomarker Measurements in German Children and Adolescents Over 3 Decades

BACKGROUND

Increases in phosphorus intake have been observed over the past years in adult populations. However, biomarker-based data are lacking on whether or not phosphorus intake also increased in children.

OBJECTIVE

The aim of this study was to examine 24-hour urinary phosphate excretion (PO4-Ex) and diet-related biomarkers potentially influencing phosphorus status in German children and adolescents from 1985 to 2015.

DESIGN

This longitudinal noninvasive biomarker-based cohort study examined 24-hour urine samples from children and adolescents of the Dortmund Nutritional and Anthropometric Longitudinally Designed Study, collected over 3 decades.

PARTICIPANTS/SETTING

Examined individuals (n = 1,057) were healthy participants of the Dortmund Nutritional and Anthropometric Longitudinally Designed Study, situated in Dortmund, Germany, who had been asked to collect one yearly 24-hour urine sample. Six thousand seven hundred thirty-seven samples collected from participants aged 3 to 17 years between 1985 (baseline) and 2015, were included.

MAIN OUTCOME MEASURES

phosphorus intake was examined biomarker-based by analyzed PO4-Ex in 24-hour urine samples. Whether acid-base status and intakes of protein, salt, and fruits and vegetables, may have relevantly contributed to PO4-Ex levels was assessed by determining 24-hour excretions of net acid, urea-nitrogen, and sodium as well as specific standardized excretions of potassium plus oxalate.

STATISTICAL ANALYSES PERFORMED

Trend analysis over 30 years and potentially influencing diet factors were examined using linear mixed-effect regression models (PROC-MIXED). Adjustments for sex, age, and body surface area were performed.

RESULTS

No change was identifiable for PO4-Ex over the 3 decades; neither in 3 to 8, 9 to 13, nor in 14 to 17 year olds. However, sodium excretion increased (P = .001). PROC-MIXED analysis on intraindividual changes in PO4-Ex revealed direct relationships with net acid excretion, urea-nitrogen, and sodium excretion and an inverse relationship with a biomarker of fruit and vegetable intake.

CONCLUSIONS

Despite a direct relationship between PO4-Ex and a biomarker of industrially processed food consumption; that is, sodium excretion, which showed an increasing time trend, phosphorus intake was found to remain stable over decades in children and adolescents.

Cohort profile update-overview of over 35 years of research in the Dortmund Nutritional and Anthropometric Longitudinally Designed (DONALD) study

PURPOSE

To provide an update on the cohort profile of the DOrtmund Nutritional and Anthropometric Longitudinally Designed (DONALD) study, including objectives, study design, methods and description of the comprehensive data pool, as well as to summarize the most important research findings of recent years.

METHODS

In 1985, the open (dynamic) cohort started to collect information on diet, growth, development, and metabolism of healthy children and adolescents in Dortmund, Germany. Detailed data are collected annually during infancy, childhood, and adolescence of the participants, including a 3-day weighed dietary record, a 24-h urine sample, anthropometric and medical examinations as well as interviews on lifestyle.

RESULTS

Even if the basic examination modules have not changed since the start over 35 years ago, the DONALD study has been continuously further developed by introducing new modules. As such, participants are also invited for follow-up examinations during adulthood since 2005, including an additional fasting blood withdrawal. Overall, 2375 (♂: 1177; ♀: 1198) participants were recruited in the DONALD study between 1985 and 2022. Data from ~ 30,700 anthropometric measurements, ~ 19,200 dietary records, ~ 10,600 24-h urine and ~ 1300 blood samples are available from an observation period of over 35 years.

CONCLUSION

The DONALD study provides a large data pool for longitudinal studies on nutrition, growth, and health in childhood and adolescence, its impact on the development of diseases in early adult life as well as dietary intake trends over more than three decades.

Chronic disease outcome metadata from German observational studies - public availability and FAIR principles

Metadata from epidemiological studies, including chronic disease outcome metadata (CDOM), are important to be findable to allow interpretability and reusability. We propose a comprehensive metadata schema and used it to assess public availability and findability of CDOM from German population-based observational studies participating in the consortium National Research Data Infrastructure for Personal Health Data (NFDI4Health). Additionally, principal investigators from the included studies completed a checklist evaluating consistency with FAIR principles (Findability, Accessibility, Interoperability, Reusability) within their studies. Overall, six of sixteen studies had complete publicly available CDOM. The most frequent CDOM source was scientific publications and the most frequently missing metadata were availability of codes of the International Classification of Diseases, Tenth Revision (ICD-10). Principal investigators' main perceived barriers for consistency with FAIR principles were limited human and financial resources. Our results reveal that CDOM from German population-based studies have incomplete availability and limited findability. There is a need to make CDOM publicly available in searchable platforms or metadata catalogues to improve their FAIRness, which requires human and financial resources.

Low bone mineralization in phenylketonuria may be due to undiagnosed metabolic acidosis

Background

Dietary intervention is to date the mainstay treatment to prevent toxic phenylalanine (Phe) accumulation in PKU patients. Despite success preventing central nervous system damage, there is increasing evidence of possible other unfavorable outcomes affecting other systems, e.g. kidney and bone; underlying mechanisms are yet to be fully elucidated.

Methods

This observational, cross-sectional and descriptive study investigated 20 adult with PKU evaluating biochemical parameters, BMD measurements and extrapolating data from 3-days food records and protein substitutes (PS) and special low protein foods (SLPF) composition.

Results

Blood gas venous analysis (VBG) indices were indicative of metabolic acidosis in 60% of PKU patients and VBG pH significantly correlated with BMD's Z-score (p-value = 0.022) even if its overall mean was in range (-1.29). Low bone mineral density for chronological age (Z-score < - 2.0) was found in 4 patients (20%). Indices of kidney function were not impaired. All used PS had a moderate excess of acidity, while SLPF were alkalizing and type/variety of consumed vegetables did not determine significant changes in acid-base equilibrium. Total intakes of potassium and magnesium were lower than expected.

Discussion

PKU patients seem to be at risk of metabolic acidosis, directly linked to possible low bone mineralization. This may be related to the acidic composition of PS, potentially capable of acidifying the entire diet. Reported low intakes of potassium and magnesium may be relevant to these observations. Further studies are needed to better address these topics.

Carbohydrate Intake and Its Association With Dietary Acid Load in U.S. Adults: Results From a Cross-Sectional Study

Background: The safety profile of low-carbohydrate diets is controversial and poorly understood. We investigated the effects of low-moderate carbohydrate intake on dietary acid load (DAL), an emerging health risk factor and novel clinical marker associated with numerous adverse clinical outcomes. Methods: We used data from the National Health and Nutrition Examination Surveys to investigate how low-moderate carbohydrate intake quantitatively affects DAL (as assessed by PRAL and NEAP scores) and to contrast the results to DAL scores in individuals that meet carbohydrate intake recommendations. Results: We analyzed data from 23 825 individuals, of which 4891 consumed a low-moderate carbohydrate diet. Said individuals derived 37.84% of energy from carbohydrates, tended to be male, had a mean BMI of 28.47 kg/m2, and consumed significantly more energy from fat and protein ( P≤.01 for both) than individuals that met carbohydrate recommendations Low-moderate carbohydrate intake was associated with a significantly higher DAL. Mean PRALR, NEAPR, and NEAPF values were 26.12, 71.02, and 68.98 mEq/d, respectively. Multivariate regression revealed the highest DAL scores in individuals on a low-carbohydrate diet, obtaining <26% of energy from carbohydrates. Conclusions: Low-moderate carbohydrate intake is associated with increased DAL scores, which has been repeatedly associated with various health repercussions.

Associations of Adherence to a Dietary Index Based on the EAT-Lancet Reference Diet with Nutritional, Anthropometric, and Ecological Sustainability Parameters: Results from the German DONALD Cohort Study

BACKGROUND

Validation of the EAT-Lancet reference diet (ELR-diet), recently proposed by the EAT-Lancet Commission, within the context of real-life studies is necessary to elucidate its feasibility, nutritional value, sustainability, and health effects.

OBJECTIVES

We aimed to develop a dietary index (DI) score to measure adherence to the ELR-diet. We further aimed to study the association between the DI score and 1) nutritional characteristics, 2) indicators of ecological sustainability, and 3) anthropometric markers and biomarkers for cardiometabolic health.

METHODS

A DI score was constructed by comparing the categories defined by the ELR-diet with the dietary data of 2-5 sets of 3-d weighed dietary records from DONALD (Dortmund Nutritional and Anthropometric Longitudinal Designed) study participants (n = 298; ≥15 y of age). Prospective associations between the DI score and risk markers (anthropometric and cardiometabolic) in young adulthood (≥18 y old) were investigated using multivariate linear regression.

RESULTS

Adherence to the DI score components was considerable (majority > 50%), but varied within the population (2%-100%). The highest tertile of the DI score was inversely associated with the intake of protein (tertile 3 compared with tertile 1: 13.5 compared with 14.5 energy %), added sugars (10.5 compared with 12.4 energy %), and cholesterol (100 compared with 116 mg/1000 kcal), but positively associated with fiber intake (10.0 compared with 8.82 g/1000 kcal) (all P < 0.05). The DI score was inversely associated with greenhouse-gas emissions (tertile 1 compared with tertile 3: 6.48 compared with 5.85 kg of carbon dioxide equivalents/2500 kcal; P < 0.001) and land use (8.24 compared with 7.16 m2 × y/2500 kcal; P < 0.001). Inverse associations between the DI score and anthropometric markers during young adulthood were observed (e.g., BMI: tertile 1 compared with tertile 3: 22.9 compared with 21.9 kg/m2; P = 0.03) (all P < 0.05). No associations between the DI score and cardiometabolic risk markers were found (all P ≥ 0.05).

CONCLUSIONS

Adherence to the ELR-diet was associated with favorable nutritional characteristics and reduced environmental impact. Adherence to the DI score in adolescence was also beneficial with respect to anthropometric markers in early adulthood, although not for further cardiometabolic risk markers.

Dietary Acid Load is Associated with Hypertension and Diabetes in the Elderly

BACKGROUND

Diet can affect the body's acid-base balance due to its content of acid or base precursors. There is conflicting evidence for the role of metabolic acidosis in the development of cardiometabolic disorders, hypertension (HT), and insulin resistance (IR).

OBJECTIVE

We hypothesize that dietary acid load (DAL) is associated with adverse metabolic risk factors and we aimed to investigate this in the elderly.

METHODS

A total of 114 elderly participants were included in the study. The participants were divided into four groups such as HT, diabetes (DM), both HT and DM, and healthy controls. Anthropometric, biochemical, and clinical findings were recorded. Potential renal acid load (PRAL) and net endogenous acid production (NEAP) results were obtained from three-day, 24-hour dietary records via a nutrient database program. (BeBiS software program).

RESULTS

The groups were matched for age, gender, and BMI. There was a statistically significant difference between the groups in terms of NEAP (p=0.01) and no significant difference for PRAL (p=0.086). The lowest NEAP and PRAL levels were seen in the control group while the highest in the HT group. Both NEAP and PRAL were correlated with waist circumference (r=0,325, p=0.001; r=0,231, p=0,016, respectively).

CONCLUSION

Our data confirmed that subjects with HT and DM had diets with greater acid-forming potential. High NEAP may be a risk factor for chronic metabolic diseases, particularly HT. PRAL couldn't be shown as a significantly different marker in all participants. Dietary content has a significant contribution to the reduction of cardiovascular risk factors such as HT, DM, and obesity.

Time-updated anion gap and cardiovascular events in advanced CKD: a cohort study

Background

Studies examining associations between metabolic acidosis and cardiovascular events in chronic kidney disease (CKD) have shown conflicting results and have not differentiated between normal anion gap (hyperchloremic) acidosis and high anion gap acidosis. We aimed to examine the impact of normal and high anion gap acidosis, separately, on the risk of cardiovascular events among patients with CKD.

Methods

This retrospective cohort study included 1168 patients with an estimated glomerular filtration rate (eGFR) of 10–60 mL/min/1.73 m² and available data on anion gap. We analyzed the association of time-updated high anion gap (anion gap ≥9.2) with the rate of cardiovascular events using marginal structural models (MSMs) to account for time-dependent confounding. We also analyzed the association between time-updated normal anion gap acidosis (anion-gap-adjusted bicarbonate level ≤22.8 mEq/L) and cardiovascular events.

Results

The mean baseline eGFR of the cohort was 28 mL/min/1.73 m². The prevalence rates of high anion gap in CKD stages G3a, G3b, G4 and G5 were 20%, 16%, 27% and 46%, respectively. During a median follow-up period of 2.9 years, 132 patients developed cardiovascular events (3.3/100 patient-years). In MSMs, high anion gap was associated with a higher rate of cardiovascular events [hazard ratio (HR) 1.87; 95% confidence interval (95% CI) 1.13‒3.09; P = 0.02] and the composite of cardiovascular events or all-cause death (HR 3.28; 95% CI 2.19‒4.91; P < 0.001). Normal anion gap acidosis was not associated with cardiovascular events (HR 0.74; 95% CI, 0.47‒1.17; P = 0.2).

Conclusions

Among patients with advanced CKD, high anion gap was associated with an increased risk of cardiovascular events.

Diet-dependent acid load associates with mean arterial pressure in a cohort of non-obese, non-black, post-menopausal women

Higher sodium (Na+) intakes are associated with higher blood pressure (BP). Whether this relationship is stronger with diet-dependent acid load (DAL) and in patients with diagnosed hypertension or normal BP is not well determined. We studied 170 postmenopausal women randomized to potassium bicarbonate or placebo till 36 months where 24-hour urine and arterialized blood were collected. We investigated the association of DAL estimated as urinary potential renal acid load (UPRAL) and mean arterial pressure (MAP) using mixed-effects model, adjusting for age, anthropometrics, creatinine clearance, and treatment. Adjusted regression estimates for change in Na+ and UPRAL on MAP after 12 months follow-up were calculated, and further adjustments were made for change in potassium (K+) and body mass index (BMI). MAP was inversely associated with UPRAL (β [95% CI]:-0.11[-0.25,-0.001]). There was effect modification by hypertension (p-interaction=0.04); MAP decreased significantly in normotensives but the association was not significant in hypertensives. A decrease of 0.70 mmHg in MAP (0.13,1.69) per 50 mmol/24 hr reduction in Na+ was noted when the model was adjusted for change in K+. Our results with UPRAL exhibited stronger dose-response for MAP, which remained significant after adjustment for BMI. UPRAL was independently associated with MAP even after adjustment for potential confounders, and the data showed this association to be more pronounced in normotensives. Novelty: • First longitudinal study on the association of UPRAL and MAP • Association was a more robust relationship than between U[Na/K] ratio and MAP • UPRAL may play a significant role in the pathogenesis of primary hypertension.

Performance of Predictive Equations and Biochemical Measures Quantifying Net Endogenous Acid Production and the Potential Renal Acid Load

Introduction

A limited number of studies have assessed the accuracy and precision of methods for determining the net endogenous acid production (NEAP) and its components. We aimed to investigate the performance of methods quantifying the diet dependent acid–base load.

Methods

Data from metabolic balance studies enabled calculations of NEAP according to the biochemical measures (of net acid excretion [NAE], urinary net endogenous acid production [_UNEAP], and urinary potential renal acid load [_UPRAL]) as well as estimative diet equations (by Frassetto et al., Remer and Manz, Sebastian et al., and Lemann) that were compared among themselves in healthy participants fed both acid and base forming diets for 6 days each.

Results

Seventeen participants (mean ± SD age, 60 ± 8 years; body mass index, 23 ± 2 kg/m²) provided 102 twenty-four-hour urine samples for analysis (NAE, 39 ± 38 mEq/d [range, −9 to 95 mEq/d]). Bland-Altman analysis comparing _UNEAP to NAE showed good accuracy (bias, −2 mEq/d [95% confidence interval {CI}, −8 to 3]) and modest precision (limits of agreement, −32 to 28 mEq/d). Accurate diet equations included potential renal acid load (PRAL) by Sebastian et al. (bias, −4 mEq/d [95% CI, −8 to 0]) as well as NEAP by Lemann et al. (bias, 4 mEq/d [95% CI, −1 to 9]) and Remer and Manz (bias, −1 mEq/d [95% CI, −6 to 3]).

Conclusions

Researchers are encouraged to collect measures of _UPRAL and _UNEAP; however, investigators drawing conclusions between the diet-dependent acid–base load and human health should consider the limitations within all methods.

Renal biomarkers of acid excretion capacity: relationships with body fatness and blood pressure

BACKGROUND

Overweight and higher BMI are known to be related to increased blood pressure (BP) and additionally associate with lowered urine pH values even at comparable total daily acid loading. Since a reduced urine pH level at a given total acid load indicates an impaired renal net acid excretion capacity (NAEC) and renal function also relates to BP, we hypothesized that NAEC may be one mediator of the body fat-BP association.

METHODS

Ammonium, titratable acid, pH, creatinine, and urea were measured in 24-h urine samples among 9-15-year-old adolescents of the DONALD Study. NAEC was determined as residual of the body surface area-corrected net acid excretion on urine pH (NAEC1) or body surface area-corrected ammonium excretion on urine pH (NAEC2). Markers of body fatness were determined anthropometrically and systolic and diastolic BP sphygmomanometrically. Multilinear regressions were used to examine cross-sectionally the body fat-NAEC and prospectively the NAEC1-BP associations.

RESULTS

All body fat parameters were inversely associated with both NAEC1 and NAEC2 among youth (P ≤ 0.01). In a separate prospective analyses, to check for possible mediation, higher adolescent NAEC1 was significantly associated with lower systolic BP in male adults only (P = 0.04), but this association was attenuated to a trend (P = 0.07) in multivariable-adjusted models.

CONCLUSIONS

Independent of systemic acid load, NAEC, i.e., the kidney's function to eliminate acids is reduced with higher body fatness, and may also contribute as a mediator in the body fatness-BP relation.

Elevated hypertension risk associated with higher dietary acid load: A systematic review and meta-analysis

BACKGROUND & AIMS

The association between dietary acid load and hypertension risk is inconclusive. We conducted a systematic review and meta-analysis to summarize effect of dietary acid load on blood pressure.

METHODS

A comprehensively search was performed in electronic databases including EMBASE, PubMed, Web of Science and Chinese National Knowledge Infrastructure. Summary ORs and their corresponding 95% CIs were computed assuming a randomized model or fixed model.

RESULTS

Ten publications comprising 4 cohort and 6 cross-sectional studies were eligible for meta-analysis. There were 8 studies about potential renal acid load (PRAL) and 4 about net endogenous acid production (NEAP). Essential hypertension was statistically associated with higher PRAL (OR = 1.14, 95% CI = 1.02-1.17). Our findings also demonstrated a positive impact of higher PRAL on elevating both diastolic pressure (WMD = 0.96, 95% CI = 0.67-1.26) and systolic pressure (WMD = 1.57, 95% CI = 1.12-2.03). A 35% increased risk of hypertension associated with higher NEAP was identified (OR = 1.35, 95% CI = 1.03-1.78).

CONCLUSIONS

The current study suggests that dietary acid load might be potential risk factor of hypertension.

Dietary acid load and cardiometabolic risk factors: a systematic review and meta-analysis of observational studies

OBJECTIVE

Dietary acid load (DAL) might contribute to change the levels of cardiometabolic risk factors; however, the results are conflicting. The present review was conducted to determine the relationship between DAL and cardiometabolic risk factors.

DESIGN

Systematic review and meta-analysis.

SETTING

A systematic search was conducted in electronic databases including ISI Web of Science, PubMed/MEDLINE, Scopus and Google Scholar for observational studies which assessed cardiometabolic risk factors across DAL. Outcomes were lipid profile, glycaemic factors and anthropometric indices. Effect sizes were derived using a fixed- or random-effect model (DerSimonian-Laird). Also, subgroup analysis was performed to find the probable source of heterogeneity. Egger's test was performed for finding any publication bias.

RESULTS

Thirty-one studies were included in the current review with overall sample size of 92 478. There was a significant relationship between systolic blood pressure (SBP; weighted mean difference (WMD) = 1·74 (95 % CI 0·25, 3·24) mmHg; P = 0·022; I2 = 95·3 %), diastolic blood pressure (DBP; WMD = 0·75 (95 % CI 0·07, 1·42) mmHg; P = 0·030; I2 = 80·8 %) and DAL in cross-sectional studies. Serum lipids, glycaemic parameters including fasting blood sugar, glycated Hb, serum insulin, homeostatic model assessment of insulin resistance and waist circumference had no significant relationship with DAL. No publication bias was found. BMI was not associated with DAL in both cross-sectional and cohort studies.

CONCLUSIONS

Higher DAL is associated with increased SBP and DBP. More studies are needed to find any relationship of DAL with lipid profile and glycaemic factors.

Dietary Acid Load: mechanisms and evidence of its health repercussions

Diet composition has long been known to influence acid-base balance by providing acid or base precursors. In general, foods rich in protein, such as meat, cheese, eggs, and others, increase the production of acid in the body, whereas fruit and vegetables increase alkalis. The capacity of acid or base production of any food is called potential renal acid load (PRAL). Diets high in PRAL induce a low-grade metabolic acidosis state, which is associated with the development of metabolic alterations such as insulin resistance, diabetes, hypertension, chronic kidney disease, bone disorders, low muscle mass and other complications. The aim of this paper is to review the available evidence which evaluates the association of the PRAL of the diet with the incidence of chronic diseases and metabolic disorders, as well as related mechanisms involved in their development.

Prospective relation of adolescent citrate excretion and net acid excretion capacity with blood pressure in young adulthood

Experimental data and observational studies in adults suggest that even subtle changes in acid-base balance, indicative of a higher systemic proton load, are related to higher blood pressure (BP) levels and an increased hypertension risk. However, these associations have not been investigated during growth. The kidney is the central organ in regulating excretion of nonvolatile acids, and renal citrate excretion has been shown to be a sensitive, noninvasive marker of changes in systemic acid balance. We thus analyzed the prospective relation of 24-h citrate excretion, as well as net acid excretion capacity (NAEC; a noninvasive indicator of the renal ability to excrete protons), during adolescence (boys: 10-15 yr; girls: 9-14 yr) with BP levels in young adulthood (18-30 yr) in 374 healthy participants of the Dortmund Nutritional and Anthropometric Longitudinally Designed (DONALD) Study. In linear-regression analyses adjusted for age, sex, 24-h urinary excretions of sodium and potassium, as well as further relevant confounders, a 1-mmol/1.73 m²/day higher adolescent citrate excretion was related to 1.2 mmHg lower systolic BP ( P = 0.02) but not to diastolic BP ( P = 0.6). A 10-mEq higher NAEC during adolescence was related to 1.7 mmHg lower systolic BP in young men, but this association was statistically nonsignificant ( P = 0.07) after multivariable adjustment. Additional adjustment for adult body mass index did not alter these findings. To conclude, subtle changes in systemic acid-base balance during adolescence are already indicative for later BP. Potential sex differences in these associations should be investigated in further studies.

Potassium Citrate Supplementation Decreases the Biochemical Markers of Bone Loss in a Group of Osteopenic Women: The Results of a Randomized, Double-Blind, Placebo-Controlled Pilot Study

The relationship involving acid-base imbalance, mineral metabolism and bone health status has previously been reported but the efficacy of the alkalizing supplementation in targeting acid overload and preventing bone loss has not yet been fully elucidated. In this randomized, double-blind, placebo-controlled study, the hypothesis that potassium citrate (K citrate) modifies bone turnover in women with postmenopausal osteopenia was tested. Three hundred and ten women were screened; 40 women met the inclusion criteria and were randomly assigned to the treatment or the placebo group. They were treated with K citrate (30 mEq day⁻¹) or a placebo in addition to calcium carbonate (500 mg day⁻¹) and vitamin D (400 IU day⁻¹). At baseline and time points of 3 and 6 months, serum indicators of renal function, electrolytes, calciotropic hormones, serum bone turnover markers (BTMs) (tartrate-resistant acid phosphatase 5b (TRACP5b), carboxy-terminal telopeptide of type I collagen (CTX), bone alkaline phosphatase (BAP), procollagen type 1 N terminal propeptide (PINP)), and urine pH, electrolytes, and citrate were measured. The follow-up was completed by 17/20 patients in the “K citrate” group and 18/20 patients in the “placebo” group. At baseline, 90% of the patients exhibited low potassium excretion in 24 h urine samples, and 85% of cases had at least one urine parameter associated with low-grade acidosis (low pH, low citrate excretion). After treatment, CTX and BAP decreased significantly in both groups, but subjects with evidence of low-grade acidosis gained significant benefits from the treatment compared to the placebo. In patients with low 24h-citrate excretion at baseline, a 30% mean decrease in BAP and CTX was observed at 6 months. A significant reduction was also evident when low citrate (BAP: −25%; CTX: −35%) and a low pH (BAP: −25%; CTX: −30%) were found in fasting-morning urine. In conclusion, our results suggested that K citrate supplementation improved the beneficial effects of calcium and vitamin D in osteopenic women with a documented potassium and citrate deficit, and a metabolic profile consistent with low-grade acidosis.

Dietary Acid Load and Potassium Intake Associate with Blood Pressure and Hypertension Prevalence in a Representative Sample of the German Adult Population

Diets rich in fruits and vegetables, like the Dietary Approaches to Stop Hypertension (DASH)-diet, are usually characterized by high potassium intake and reduced dietary acid load, and have been shown to reduce blood pressure (BP). However, the relevance of potential renal acid load (PRAL) for BP has not been compared with the relevance to BP of urinary biomarker (K-urine)- and dietary food frequency questionnaire (K-FFQ)-based estimates of potassium intake in a general adult population sample. For 6788 participants (aged 18–79 years) of the representative German Health-Interview and Examination Survey for Adults (DEGS1), associations of PRAL, K-urine, and K-FFQ with BP and hypertension prevalence were cross-sectionally examined in multivariable linear and logistic regression models. PRAL was significantly associated with higher systolic BP (p = 0.0002) and higher hypertension prevalence (Odds ratio [OR] high vs. low PRAL = 1.45, p = 0.0004) in models adjusted for age, sex, body mass index (BMI), estimated sodium intake, kidney function, relevant medication, and further important covariates. Higher estimates of K-FFQ and K-urine were related to lower systolic BP (p = 0.04 and p < 0.0001) and lower hypertension prevalence (OR = 0.82, p = 0.04 and OR = 0.77, p = 0.02) as well as a lower diastolic BP (p = 0.03 and p = 0.0003). Our results show, for the first time in a comparative analysis of a large representative population sample, significant relationships of BP and hypertension prevalence with questionnaire- and biomarker-based estimates of potassium intake and with an estimate of dietary acid load.

Dietary Potential Renal Acid Load Is Positively Associated with Serum Uric Acid and Odds of Hyperuricemia in the German Adult Population

Background

Initial interventional data indicate that a reduction in dietary acid load (e.g., by an increased consumption of alkalizing fruit and vegetables) can increase renal uric acid excretion and decrease serum uric acid (SUA).

Objective

Against this background, we examined the association between dietary potential renal acid load (PRAL) and SUA in a representative population sample.

Methods

Cross-sectional analyses were performed in 6894 participants (aged 18-79 y) of the German Health Interview and Examination Survey for Adults (DEGS1). Dietary intake was assessed with a food-frequency questionnaire. Nutritive acid load and the intake of uric acid equivalents (UAEs) were characterized by assigning PRAL and UAE values to reported food consumption. In multiple linear regression models, the associations of PRAL, UAEs, and relevant food groups with SUA were analyzed. Multiple logistic regressions were used to calculate ORs for hyperuricemia comparing lower and upper tertiles of the predictors.

Results

After adjustment for relevant confounders, PRAL (P = 0.003), alcohol (P < 0.0001), and UAE (P = 0.03) intakes were positively associated with SUA, whereas the intake of dairy products and fruit and vegetables was inversely associated (both P < 0.0001). Subgroup analyses among participants without interacting medication use confirmed these results. In addition, participants with lower PRAL had lower odds for hyperuricemia (OR: 0.60; 95% CI: 0.43, 0.83).

Conclusions

Apart from observing known dietary influences on SUA, we found in this population-based, cross-sectional study in adults that low PRAL may represent a potentially SUA-reducing dietary pattern. This highlights dietary alkalization as a possible nonpharmacologic option to influence elevated SUA concentrations.

Metabolic acidosis of chronic kidney disease and subclinical cardiovascular disease markers: Friend or foe?

The effect of chronic metabolic acidosis (MA) on cardiovascular disease (CVD) in the setting of chronic kidney disease (CKD) is largely unknown. Therefore, we aimed to study this relationship in nondialysis CKD patients.This cross-sectional, single-center study prospectively enrolled 95 clinically stable CKD patients (median age 61 (58, 65) years, 60% male, median eGFR 27 (22, 32) mL/min). Data on CKD etiology, CVD history, CVD traditional, and nontraditional risk factors were obtained. Also, markers of subclinical CVD were assessed: intima-media thickness (IMT), abdominal aortic calcifications (Kauppila score-AACs), cardio-ankle vascular index (CAVI), ankle-brachial index (ABI), ejection fraction, and interventricular septum thickness. Using the serum bicarbonate cutoff value of 22 mEq/L, comparisons between MA (<22 mEq/L; 43 patients) and non-MA (≥22 mEq/L; 52 patients) groups were performed.Vascular (40%), tubulointerstitial (24%), and glomerular (22%) nephropathies were the main causes of CKD. Twenty-three percent of patients had diabetes mellitus, but only 5% were considered to have diabetic nephropathy. Patients with chronic MA had lower eGFR (P < .01), higher iPTH (P = .01), higher serum phosphate (P < .01), and increased serum cholesterol (P = .04) and triglycerides (P = .01).Higher ABI (P = .04), lower IMT (P = .03), CAVI (P = .05), and AACs (P = .03) were found in patients with chronic MA.Separate binomial logistic regression models were performed using ABI (cutoff 0.9), CAVI (cutoff 9), IMT (cutoff 0.1 cm), and AACs (cutoff 1) as dependent variables. MA was used as independent variable and adjustments were made for iPTH, serum phosphate, eGFR, proteinuria, cholesterol, triglycerides, CVD score. The absence of MA was retained as an independent predictor only for the presence of AACs.In conclusion, the present study shows a potential advantageous effect of MA on vascular calcifications in predialysis CKD patients. Thus, a guideline relaxation of the serum bicarbonate target might prove to be beneficial in CKD patients at high risk of vascular calcifications. However, one should always consider the negative effects of MA. Therefore, additional research is warranted before any clear clinical recommendation.

Adverse Effects of the Metabolic Acidosis of Chronic Kidney Disease

The kidney has the principal role in the maintenance of acid-base balance, and therefore, a fall in renal net acid excretion and positive H+ balance often leading to reduced serum [HCO3-] are observed in the course of CKD. This metabolic acidosis can be associated with muscle wasting, development or exacerbation of bone disease, hypoalbuminemia, increased inflammation, progression of CKD, protein malnutrition, alterations in insulin, leptin, and growth hormone, and increased mortality. Importantly, some of the adverse effects can be observed even in the absence of overt hypobicarbonatemia. Administration of base decreases muscle wasting, improves bone disease, restores responsiveness to insulin, slows progression of CKD, and possibly reduces mortality. Base is recommended when serum [HCO3-] is <22 mEq/L, but the target serum [HCO3-] remains unclear. Evidence that increments of serum [HCO3-] >26 mEq/L might be associated with worsening of cardiovascular disease adds complexity to treatment decisions. Further study of the mechanisms through which positive H+ balance in CKD contributes to its various adverse effects and the pathways involved in mediating the benefits and complications of base therapy is warranted.

Urinary pH reflects dietary acid load in patients with type 2 diabetes

Dietary acid load is important information, however, survey of food intake needs time and skill. Therefore, it is difficult to survey food intake from all patients. It remains to be elucidated the association between dietary acid load and urinary pH in patients with type 2 diabetes. In this cross-sectional study of 173 patients, we investigated the relationship between urinary pH and dietary acid load, assessed with potential renal acid load. Habitual food and nutrient intake was assessed by a self-administered diet history questionnaire. Urinary pH was negatively correlated with potential renal acid load (r = –0.24, p = 0.002). Multivariate regression analysis revealed that potential renal acid load (standardized regression coefficient = –0.21, p = 0.036) was associated with urinary pH after adjusting for covariates. In addition, according to the receiver operator characteristic analysis, the optimal cut-off point of urinary pH for high dietary acid load, defined as potential renal acid load over 7.0 mEq/day was 5.7 (area under the receiver operator characteristic curve 0.63 (95% CI 0.54–0.71), sensitivity = 0.56, specificity = 0.70, p = 0.004). Urinary pH was associated with dietary acid load in patients with type 2 diabetes. We suggest that urinary pH can be a practical screening marker for dietary acid load in patients with type 2 diabetes.

Role of Acid-Base Homeostasis in Diabetic Kidney Disease

PURPOSE OF REVIEW

Acid-base homeostasis is impaired in chronic kidney disease (CKD) and may contribute to disease progression. Diabetes, a major cause of CKD worldwide, may exacerbate acidosis further due to differences in acid production and excretion. Here, we review the role of abnormal acid-base homeostasis in the pathogenesis and progression of diabetes and diabetic kidney disease.

RECENT FINDINGS

Acidosis and dietary acid loading may contribute to the development and worsening of insulin resistance and hypertension, thereby promoting diabetes and diabetic CKD. However, although metabolic acidosis associates with progression of CKD generally, the results in diabetic CKD are mixed. Data suggests that metabolic acid production in diabetes may be higher than would be predicted based on dietary intake alone, and new observational data suggests that this higher diet-independent acid production could potentially be protective. The role of acid-base homeostasis in diabetic CKD progression is complex and must consider differences in endogenous acid production and excretion in diabetes. Ongoing observational and interventional studies in this field should consider the unique physiology of diabetes.

Dietary acid load and blood pressure development in pregnancy: The Generation R Study

BACKGROUND & AIMS

Dietary intake could induce a mild maternal metabolic acidosis that might lead to a higher level of blood pressure. Because studies in pregnancy are scarce, we evaluated the association between maternal dietary acid load and changes in blood pressure during pregnancy, pregnancy-induced hypertension and pre-eclampsia.

METHODS

We included 3411 pregnant women of Dutch ancestry from a prospective population-based cohort (Rotterdam, The Netherlands). Dietary data was self-reported via a food-frequency questionnaire in early pregnancy. Four dietary acid load measurements were calculated: dietary potential renal acid load (dPRAL), net endogenous acid production (NEAP), animal protein/potassium ratio, and vegetable protein/potassium ratio. Diastolic blood pressure (DBP) and systolic blood pressure (SBP) were measured three times during pregnancy. Information on pregnancy-induced hypertension and pre-eclampsia was obtained from medical records. Linear mixed models and logistic regression were used and adjusted for sociodemographic and lifestyle factors.

RESULTS

The results indicated that dPRAL, NEAP and animal protein/potassium ratio were not associated with DBP or SBP in pregnancy. One standard deviation higher vegetable protein/potassium ratio was associated with lower DBP (-0.30 mmHg [95% CI -0.54; -0.06]) but not with SBP (-0.29 mmHg [95% CI -0.60; 0.01]). Dietary acid load measurement was neither associated with the prevalence of pregnancy-induced hypertension nor with pre-eclampsia.

CONCLUSIONS

Dietary acid load was not associated with changes in DBP or SBP during pregnancy, although women with a higher vegetable protein/potassium ratio had a slightly lower DBP. Dietary acid load was not associated with pregnancy-induced hypertension or pre-eclampsia.

Deletion of proton-sensing receptor GPR4 associates with lower blood pressure and lower binding of angiotensin II receptor in SFO

Diets rich in grains and meat and low in fruits and vegetables (acid-producing diets) associate with incident hypertension, whereas vegetarian diets associate with lower blood pressure (BP). However, the pathways that sense and mediate the effects of acid-producing diets on BP are unknown. Here, we examined the impact of the deletion of an acid sensor GPR4 on BP. GPR4 is a proton-sensing G protein-coupled receptor and an acid sensor in brain, kidney, and blood vessels. We found that GPR4 mRNA was higher in subfornical organ (SFO) than other brain regions. GPR4 protein was abundant in SFO and present in capillaries throughout the brain. Since SFO partakes in BP regulation through the renin-angiotensin system (RAS), we measured BP in GPR4-/- and GPR4+/+ mice and found that GPR4 deletion associated with lower systolic BP: 87 ± 1 mmHg in GPR4-/- (n = 35) vs. 99 ± 2 mmHg (n = 29) in GPR4+/+; P < 0.0001, irrespective of age and sex. Angiotensin II receptors detected by ¹²⁵I-Sarthran binding were lower in GPR4-/- than GPR4+/+ mice in SFO and in paraventricular nucleus of hypothalamus. Circulating angiotensin peptides were comparable in GPR4-/- and GPR4+/+ mice, as were water intake and excretion, serum and urine osmolality, and fractional excretion of sodium, potassium, or chloride. A mild metabolic acidosis present in GPR4-/- mice did not associate with elevated BP, implying that deficiency of GPR4 may preclude the effect of chronic acidosis on BP. Collectively, these results posit the acid sensor GPR4 as a novel component of central BP control through interactions with the RAS.

Effect of increased protein intake on renal acid load and renal hemodynamic responses

Increased protein intake versus maltodextrin intake for 4 weeks lowers blood pressure. Concerns exist that high‐protein diets reduce renal function. Effects of acute and 4‐week protein intake versus maltodextrin intake on renal acid load, glomerular filtration rate and related parameters were compared in this study. Seventy‐nine overweight individuals with untreated elevated blood pressure and normal kidney function were randomized to consume a mix of protein isolates (60 g/day) or maltodextrin (60 g/day) for 4 weeks in energy balance. Twenty‐four‐hour urinary potential renal acid load (uPRAL) was compared between groups. A subgroup (maltodextrin N = 27, protein mix N = 25) participated in extra test days investigating fasting levels and postprandial effects of meals supplemented with a moderate protein‐ or maltodextrin‐load on glomerular filtration rate, effective renal plasma flow, plasma renin, aldosterone, pH, and bicarbonate. uPRAL was significantly higher in the protein group after 4 weeks (P ≤ 0.001). Postprandial filtration fraction decreased further after the protein‐supplemented breakfast than after the maltodextrin‐supplemented breakfast after 4 weeks of supplementation (P ≤ 0.001). Fasting and postprandial levels of glomerular filtration rate, effective renal plasma flow, renin, aldosterone, angiotensin‐converting enzyme, pH and bicarbonate did not differ between groups. In conclusion, 4 weeks on an increased protein diet (25% of energy intake) increased renal acid load, but did not affect renal function. Postprandial changes, except for filtration fraction, also did not differ between groups. These data suggest that a moderate increase in protein intake by consumption of a protein mix for 4 weeks causes no (undesirable) effects on kidney function in overweight and obese individuals with normal kidney function.

Glucocorticoid activity and metabolism with NaCl-induced low-grade metabolic acidosis and oral alkalization: results of two randomized controlled trials

Low-grade metabolic acidosis (LGMA), as induced by high dietary acid load or sodium chloride (NaCl) intake, has been shown to increase bone and protein catabolism. Underlying mechanisms are not fully understood, but from clinical metabolic acidosis interactions of acid-base balance with glucocorticoid (GC) metabolism are known. We aimed to investigate GC activity/metabolism under alkaline supplementation and NaCl-induced LGMA. Eight young, healthy, normal-weight men participated in two crossover designed interventional studies. In Study A, two 10-day high NaCl diet (32 g/d) periods were conducted, one supplemented with 90 mmol KHCO3/day. In Study B, participants received a high and a low NaCl diet (31 vs. 3 g/day), each for 14 days. During low NaCl, the diet was moderately acidified by replacement of a bicarbonate-rich mineral water (consumed during high NaCl) with a non-alkalizing drinking water. In repeatedly collected 24-h urine samples, potentially bioactive-free GCs (urinary-free cortisol + free cortisone) were analyzed, as well as tetrahydrocortisol (THF), 5α-THF, and tetrahydrocortisone (THE). With supplementation of 90 mmol KHCO3, the marker of total adrenal GC secretion (THF + 5α-THF + THE) dropped (p = 0.047) and potentially bioactive-free GCs were reduced (p = 0.003). In Study B, however, GC secretion and potentially bioactive-free GCs did not exhibit the expected fall with NaCl-reduction as net acid excretion was raised by 30 mEq/d. Diet-induced acidification/alkalization affects GC activity and metabolism, which in case of long-term ingestion of habitually acidifying western diets may constitute an independent risk factor for bone degradation and cardiometabolic diseases.

Estimated net endogenous acid production and risk of prevalent and incident hypertension in community-dwelling older people

AIM: To investigate the associations of dietary acid-base load with prevalent and incident hypertension in community-living Chinese older adults in Hong Kong.

METHODS: Participants aged ≥ 65 years participating in a cohort study examining the risk factors for osteoporosis completed a validated food frequency questionnaire (FFQ) at baseline between 2001 and 2003. Estimated net endogenous acid production (NEAP) was calculated using Frassetto’s method based on the diet’s protein to potassium ratio derived from the FFQ. Prevalent and 4-year incident hypertension was defined as systolic blood pressure ≥ 140 mmHg and/or diastolic blood pressure ≥ 90 mmHg and/or self-reported use of anti-hypertensive medications. Multivariable logistic regression was used for cross-sectional analysis (n = 3956) to assess the association between estimated NEAP and prevalent hypertension, and for longitudinal analysis (n = 795) on its association with 4-year incident hypertension, with adjustment for various potential socio-demographic and lifestyle factors.

RESULTS: Median estimated NEAP of the participants was 47.7 (interquartile range: 36.2, 60.9) g/mEq. Participants in the highest quartile of energy-adjusted estimated NEAP was associated with increased likelihood of prevalent hypertension than those in the lowest quartile of energy-adjusted estimated NEAP [multivariable OR = 1.66 (95%CI: 1.22 to 2.26, P_trend = 0.002)]. No significant association was observed between energy-adjusted estimated NEAP and risk of incident hypertension.

CONCLUSION: A high dietary acid load was independently associated with an increased likelihood of prevalent hypertension in ambulant older Chinese people in Hong Kong. The longitudinal analyses failed to show any causal relationship between dietary acid load and hypertension in this population.

Metabolic Acidosis of CKD: An Update

The kidney has the principal role in the maintenance of acid-base balance. Therefore, a decrease in renal ammonium excretion and a positive acid balance often leading to a reduction in serum bicarbonate concentration are observed in the course of chronic kidney disease (CKD). The decrease in serum bicarbonate concentration is usually absent until glomerular filtration rate decreases to <20 to 25mL/min/1.73 m(2), although it can develop with lesser degrees of decreased kidney function. Non-anion gap acidosis, high-anion gap acidosis, or both can be found at all stages of CKD. The acidosis can be associated with muscle wasting, bone disease, hypoalbuminemia, inflammation, progression of CKD, and increased mortality. Administration of base may decrease muscle wasting, improve bone disease, and slow the progression of CKD. Base is suggested when serum bicarbonate concentration is <22 mEq/L, but the target serum bicarbonate concentration is unclear. Evidence that increments in serum bicarbonate concentration > 24 mEq/L might be associated with worsening of cardiovascular disease adds complexity to treatment decisions. Further study of the mechanisms through which metabolic acidosis contributes to the progression of CKD, as well as the pathways involved in mediating the benefits and complications of base therapy, is warranted.

Estimated dietary acid load is not associated with blood pressure or hypertension incidence in men who are approximately 70 years old

BACKGROUND

Dietary acid load affects acid-base homeostasis, which may be associated with blood pressure (BP). Previous research on dietary acid load and BP in the community has provided conflicting results, which may be confounded by underlying kidney function with inability to eliminate acid excess.

OBJECTIVE

The objective of this study was to determine whether dietary acid load is associated with blood pressure or the incidence of hypertension in older men taking into account each individual's kidney function.

METHODS

We included 673 men aged 70-71 y and not receiving antihypertensive medication from the Uppsala Longitudinal Study of Adult Men. Of those, 378 men were re-examined after 7 y. Dietary acid load was estimated at baseline by potential renal acid load (PRAL) and net endogenous acid production (NEAP), based on nutrient intake assessed by 7-d food records at baseline. Ambulatory blood pressure monitoring (ABPM) was performed at both visits. Cystatin C-estimated kidney function allowed identification of underlying chronic kidney disease.

RESULTS

Median estimated PRAL and NEAP were 3.3 and 40.7 mEq/d, respectively. In cross-section, PRAL was in general not associated with ABPM measurements (all P > 0.05, except for the 24-h diastolic BP). During follow-up, PRAL did not predict ABPM changes (all P > 0.05). When individuals with baseline hypertension (ABPM ≥ 130/80 mm Hg) or nondippers (with nighttime-to-daytime systolic BP ratio > 0.9) were excluded, PRAL was not a predictor of incident cases (P > 0.30). Kidney function did not modify these null relations. Similar findings were obtained with the use of NEAP as the exposure.

CONCLUSION

Our analyses linking estimated dietary acid load with BP outcome measurements both cross-sectionally and after 7 y in community-based older Swedish men of similar age did not reveal an association between dietary acid load and BP.

Effect of diet composition on acid-base balance in adolescents, young adults and elderly at rest and during exercise

BACKGROUND

Diets rich in animal protein and cereal grains and deficient in vegetables and fruits may cause low-grade metabolic acidosis, which may impact exercise and health. We hypothesized that (1) a normal-protein diet with high amount of vegetables and fruits (HV) induces more alkaline acid-base balance compared with a high-protein diet with no vegetables and fruits (HP) and (2) diet composition has a greater impact on acid-base balance in the elderly (ELD).

SUBJECTS/METHODS

In all, 12-15 (adolescents (ADO)), 25-35 (young adults (YAD)) and 60-75 (ELD)-year-old male and female subjects (n=88) followed a 7-day HV and a 7-day HP in a randomized order and at the end performed incremental cycle ergometer tests. We investigated the effect of diet composition and age on capillary (c-pH) and urine pH (u-pH), strong ion difference (SID), partial pressure of carbon dioxide (pCO2) and total concentration of weak acids (Atot). Linear regression analysis was used to examine the contribution of SID, pCO2 and Atot to c-pH.

RESULTS

In YAD and ELD, c-pH (P⩽0.038) and u-pH (P<0.001) were higher at rest after HV compared with HP. During cycling, c-pH was higher (P⩽0.034) after HV compared with HP at submaximal workloads in YAD and at 75% of VO2max (maximal oxygen consumption) in ELD. The contribution of SID, pCO2 and Atot to c-pH varied widely. Gender effects or changes in acid-base balance of ADO were not detected.

CONCLUSIONS

A high intake of vegetables and fruits increases blood and u-pH in YAD and ELD. ELD compared with younger persons may be more sensitive for the diet-induced acid-base changes.