Association of prevalent hypertension with 24-hour urinary excretion of calcium, citrate, and other factors

Dietary acid load in health and disease

Maintaining an appropriate acid-base equilibrium is crucial for human health. A primary influencer of this equilibrium is diet, as foods are metabolized into non-volatile acids or bases. Dietary acid load (DAL) is a measure of the acid load derived from diet, taking into account both the potential renal acid load (PRAL) from food components like protein, potassium, phosphorus, calcium, and magnesium, and the organic acids from foods, which are metabolized to bicarbonate and thus have an alkalinizing effect. Current Western diets are characterized by a high DAL, due to large amounts of animal protein and processed foods. A chronic low-grade metabolic acidosis can occur following a Western diet and is associated with increased morbidity and mortality. Nutritional advice focusing on DAL, rather than macronutrients, is gaining rapid attention as it provides a more holistic approach to managing health. However, current evidence for the role of DAL is mainly associative, and underlying mechanisms are poorly understood. This review focusses on the role of DAL in multiple conditions such as obesity, cardiovascular health, impaired kidney function, and cancer.

A high dietary acid load can potentially exacerbate cardiometabolic risk factors: An updated systematic review and meta-analysis of observational studies

AIMS

Chronic metabolic acidosis has been shown to be associated with cardiometabolic risk factors. The aim of the currently updated meta-analysis was to explore the association between Potential Renal Acid Load (PRAL) and Net Endogenous Acid Production (NEAP) with these risk factors.

DATA SYNTHESIS

Databases were searched up to May 2023. The mean of waist circumference (WC), body mass index (BMI), high- and low-density lipoprotein-cholesterol (HDL-C and LDL-C), triglyceride (TG), total cholesterol (TC), fasting blood sugar (FBS), and systolic- and diastolic blood pressure (SBP and DBP) in highest category vs lowest categories of NEAP and PRAL were recorded. Effect sizes were generated as weighted mean difference (WMD). Results showed that SBP, DBP, and WC had a significant difference in the upper and lower categories of PRAL (WMDSBP: 1.466 mmHg; 95% CI: 2.121, -0.811; P<0.001, WMDDBP: 0.710 mmHg; 95 % CI: 1.170, -0.249; P=0.003, and WMDWC: 0.819 cm; 95% CI: 1.446, -0.192; P=0.010) or NEAP (WMDSBP: 1.690 mmHg; 95% CI: 2.789, -0.591; P=0.003, WMDDBP: 1.076 mmHg, and WMDWC: 1.325 cm; 95% CI: 1.901, -0.749; P<0.001; 95% CI: 1.938, -0.214; P =0.014). The lowest versus highest categories of dietary PRAL were associated with lower BMI (WMDPRAL: 0.297 kg/m2; 95 % CI: 0.440, -0.154; P<0.001) and TG (WMD: 2.280 mg/dl; 95%CI: 3.828, -0.732; P=0.004; I2=99.4 %; P<0.001).

CONCLUSIONS

High DAL can be considered as an independent risk factor for increasing anthropometric indices, blood pressure, and TG. This study registered in the PROSPERO database (Registration No. CRD42023402985).

Sleep and circadian rhythm disturbance in kidney stone disease: a narrative review

The circadian rhythm generated by circadian clock genes functions as an internal timing system. Since the circadian rhythm controls abundant physiological processes, the circadian rhythm evolved in organisms is salient for adaptation to environmental change. A disturbed circadian rhythm is a trigger for numerous pathological events. Recently, accumulated data have indicated that kidney stone disease (KSD) is related to circadian rhythm disturbance. However, the mechanism between them has not been fully elucidated. In this narrative review, we summarized existing evidence to illustrate the possible association between circadian rhythm disturbance and KSD based on the epidemiological studies and risk factors that are linked to circadian rhythm disturbance and discuss some chronotherapies for KSD. In summary, KSD is associated with systemic disorders. Metabolic syndrome, inflammatory bowel disease, and microbiome dysbiosis are the major risk factors supported by sufficient data to cause KSD in patients with circadian rhythm disturbance, while others including hypertension, vitamin D deficiency, parathyroid gland dysfunction, and renal tubular damage/dysfunction need further investigation. Then, some chronotherapies for KSD were confirmed to be effective, but the molecular mechanism is still unclear.

Dietary acid load and cardiovascular diseases

Diet affects the body's acid-base balance by providing acid or alkali precursors in the metabolism. The importance of the acid-base balance of the diet for cardiovascular diseases, which have become the most important cause of morbidity on the global scale, has started to take its place in the literature. The prediction of endogenous acid production in dietary acid-base balance is expressed as dietary acid load. Although the available information about the effect of dietary acid load on cardiovascular diseases is limited, possible mechanisms are indicated as excessive calcium and magnesium excretion from the kidneys, reduced urinary citrate excretion, and excessive cortisol production. Metabolic acidosis has an important role in the development of cardiometabolic abnormalities, especially insulin resistance. Studies examining the relationship between dietary acid load and cardiovascular disease are limited and there is an inconsistency between studies. Practices for determining risk factors for cardiovascular diseases and preventing their effects are very important for the protection and improvement of health. Considering dietary acid load when planning a diet for individuals with cardiovascular diseases can help increase the effectiveness of the diet. The purpose of this review is to examine the effect of dietary acid load on cardiovascular diseases.

Is the METS-IR Index a Potential New Biomarker for Kidney Stone Development?

OBJECTIVE

The purpose of this study was to examine whether the METS-IR index is associated with kidney stones in American adults.

METHOD

Participants from the National Health and Nutrition Examination Survey (NHANES) database from 2007-2018 were selected for logistic regression analysis, subgroup analyses, and the calculation of dose-response curves to assess the association between the METS-IR index and the incidence of kidney stones.

RESULT

This study enrolled 30,612 adults aged >20 years, 2901 of whom self-reported having had kidney stones in the past. And, after controlling for potential confounders, each unit increase in the METS-IR index was linked with a 1.23 percent rise in kidney stone incidence (OR= 1.0123, 95% CI: 1.0092 - 1.0155), with stratified analysis indicating that this was true in all subgroups. Between all groups, an elevated METS-IR index was related to kidney stone formation, and the dose-response curve revealed a positive non-linear connection between METS-IR index and kidney stone risk, with a threshold effect analysis revealing an inflection point value of 50.8314.

CONCLUSION

Higher METS-IR index is associated with the occurrence of kidney stones,and while no causative association can be shown, this is cause for concern.

Relationship between urine specific gravity and the prevalence rate of kidney stone

Background

The purpose of this study was to evaluate the relationship between urine specific gravity (USG) and the prevalence rate of kidney stone.

Methods

We conducted a cross-sectional study of adult participants (≥20 years) of the National Health and Nutrition Examination Survey (NHANES) from 2007 to 2008. The USG was divided into three groups: <1.008, 1.008-1.020 and >1.020. Univariate and multivariate logistic regression analysis was used to determine the effect of USG on the prevalence rate of kidney stone.

Results

A total of 4,791 patients were included in this study, of which 464 (9.7%) reported a history of kidney stone. Univariate logistic regression analysis showed that age, gender, race, hypertension, diabetes, body mass index (BMI), estimated glomerular filtration rate (eGFR), USG and urine creatinine were closely related to the prevalence of kidney stones. After adjusting for known confounding factors, multivariate logistic regression showed that the prevalence rate of kidney stone increased with the increase of USG (1.008-1.020 vs. <1.008, OR =1.31, 95% CI, 0.09-1.91, P=0.155; >1.020 vs. <1.008, OR =1.71, 95% CI, 1.16-2.54, P=0.007).

Conclusions

The increase of USG was significantly correlated with self-reported kidney stone. This finding helps to identify risk factors for kidney stones as early as possible in the United States.

Dietary Acid Load and Cardiometabolic Risk Factors-A Narrative Review

The Western, diet rich in acidogenic foods (e.g., meat, fish and cheese) and low in alkaline foods (e.g., vegetables, fruits and legumes), is deemed to be a cause of endogenous acid production and elevated dietary acid load (DAL), which is a potential cause of metabolic acidosis. Multiple authors have suggested that such a dietary pattern increases the excretion of calcium and magnesium, as well as cortisol secretion. In addition, it is associated with decreased citrate excretion. All of these seem to increase blood pressure and insulin resistance and may contribute to the development of cardiometabolic disorders. However, there are inconsistencies in the results of the studies conducted. Therefore, this narrative literature review aims to present the outcomes of studies performed in recent years that investigated the association between DAL and the following cardiometabolic risk factors: blood pressure, hypertension, carbohydrate metabolism and lipid profile. Study outcomes are divided into (i) statistically significant positive association, (ii) statistically significant inverse association, and (iii) no statistically significant association.

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.

Association between hypertension and 24-h urine composition in adults without urolithiasis in China

PURPOSE

To explore the association between hypertension and 24-h urine composition in adults without urolithiasis in China.

MATERIALS AND METHODS

Blood test and 24-h urine analysis were performed on 958 non-stone formers in six cities to select eligible participants. Eligible participants were divided into hypertension group and non-hypertension group according to WHO guidelines. The 24-h urine compositions between two groups were compared using univariate and multivariate logistic regressions.

RESULTS

A total of 584 adults without urolithiasis were included in this analysis. Compared with non-hypertension group, hypertension group had significantly older age, higher BMI, higher prevalence of diabetes mellitus and higher levels of total cholesterol and LDL, but lower eCCr value, lower levels of serum creatinine and serum sodium (all P value < 0.05). In univariable comparisons, hypertension patients had significantly higher level of urine potassium (mean difference [MD] = - 3.89 mmol, 95% confidence interval [CI] - 7.37 to - 0.42, P = 0.014) but lower levels of urine creatinine (MD = 0.80 mmol, 95% CI 0.21-1.39, P = 0.004) and pH (MD = 0.12, 95% CI - 0.01 to 0.25, P = 0.033) than non-hypertension adults. However, no significant difference was found in all 24-h urinary components between two groups (all P value > 0.05) in multivariate Logistic regression analyses.

CONCLUSIONS

Our study demonstrated that hypertension did not independently influence the 24-h urine composition in adults without urolithiasis in China; however, we cannot make such an arbitrary conclusion that hypertension was not a risk factor for urolithiasis.

High dietary acid load score is not associated with the risk of metabolic syndrome in Iranian adults

Background and objective: The association between dietary acid load and metabolic syndrome (MetS) risk is not well-known. Therefore, we aimed to investigate the relationship between dietary acid load and the risk of MetS among Iranian adults. Methods: This cross-sectional study was carried out on 1430 Iranian adults. Dietary intakes were assessed using a validated food frequency questionnaire. Dietary acid load was estimated using potential renal acid load (PRAL) and net endogenous acid production (NEAP). MetS was defined according to the ATP-III criteria. The risk of MetS and its components was explored using logistic regression test. Results: Totally, 205 individuals were identified to have MetS. No significant association for MetS was found across the quartiles of PRAL and NEAP either in the crude model [Q4 PRAL: OR (95% CI): 0.94 (0.67-1.32), and NEAP: OR (95% CI): 0.88 (0.63-1.25)] or fully-adjusted model [Q4 PRAL: OR (95% CI): 0.90 (0.61-1.33), and NEAP: OR (95% CI): 1.05 (0.70-1.57)]. Amongst the components of MetS, higher scores of NEAP was associated with an increased risk of impaired blood sugar after adjustment for potential confounders [OR (95% CI): 1.35 (0.93-1.96)]. No significant association was found for other components either with PRAL or with NEAP. Conclusion: Our findings suggest no association between dietary acid load and MetS risk in Iranian adults. However, higher dietary acid load, measured by NEAP, but not PRAL, was associated with increased risk of impaired fasting blood sugar. Longitudinal studies are warranted to explore whether a diet low in potential acid load could reduce MetS risk.

Dietary acid load and risk of hypertension: A systematic review and dose-response meta-analysis of observational studies

BACKGROUND AND AIM

Previous studies have assessed diet-induced mild metabolic acidosis in relation to blood pressure, however, data are conflicting. Current systematic review and dose-response meta-analysis aimed to summarize earlier findings from observational studies on the association between dietary acid load and hypertension.

METHODS AND RESULTS

We searched the online databases for relevant publications up to Feb 2019, using relevant keywords. Overall, 14 studies (3 prospective and 11 cross-sectional studies) that included 306,183 individuals and 62,264 cases of hypertension were included in the current meta-analysis. Combining effect sizes from both prospective and cross-sectional studies revealed no significant non-linear association between dietary acid load (based on net endogenous acid production (NEAP) method) and hypertension. However, stratified analysis based on study design showed a significant non-linear association between dietary acid load and hypertension in prospective studies (P = 0.006), but not cross-sectional ones. According to linear dose-response analysis, no significant association was found between dietary acid load (based on NEAP) and hypertension (combined effect size: 1.01, 95% CI: 0.97-1.06, P = 0.51). In terms of dietary acid load based on potential renal acid load (PRAL) method, no significant non-linear association was seen with hypertension (P = 0.52). However, in linear dose-response analysis, a-20 unit increase in PRAL values was associated with 3% increased risk of hypertension (combined effect size: 1.03, 95% CI: 1.00-1.06, P = 0.03).

CONCLUSION

We found a significant positive association between dietary acid load and hypertension. Further studies, particularly those with prospective nature, are needed to confirm our findings.

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.

New-onset metabolic risk factors and the incidence of kidney stones: a prospective cohort study

OBJECTIVE

To examine the association of kidney stones with new-onset hypertension, diabetes and obesity.

PARTICIPANTS AND METHODS

This prospective cohort study included participants in the Qingdao Port Cardiovascular Health Study who were aged ≥18 years and had abdominal ultrasonography results in 2013 that were negative for kidney stones. Multivariable Cox regression models with time-dependent covariates were used to estimate the effects of new-onset hypertension, diabetes and obesity on the incidence of kidney stones.

RESULTS

There were 9667 participants without kidney stones in 2013 (mean age 46.2 years; 75.6% men). During a mean (range) follow-up of 33.5 (6-42) months, 676 (7.0%) incident cases of kidney stones were identified. Kidney stones were more frequent among those who had new-onset of a metabolic factor vs those who did not (hypertension: 7.7 vs 6.0%; diabetes: 8.4 vs 6.6%; obesity: 7.4 vs 6.8%). Adjusted Cox models identified that increased risk of kidney stones was associated with new-onset hypertension (adjusted hazard ratio [HR] 1.69, 95% confidence interval [CI] 1.25-2.27), new-onset diabetes (HR 1.78, 95% CI 1.07-2.96), and new-onset obesity (HR 1.78, 95% CI 1.15-2.74).

CONCLUSIONS

New-onset of hypertension, diabetes and obesity were all strongly associated with an increased risk of kidney stones in this prospective cohort study. Results suggest that a substantial proportion of kidney stones are potentially preventable by appropriate control of these metabolic risk factors.

Systemic Succinate Homeostasis and Local Succinate Signaling Affect Blood Pressure and Modify Risks for Calcium Oxalate Lithogenesis

BACKGROUND

In the kidney, low urinary citrate increases the risk for developing kidney stones, and elevation of luminal succinate in the juxtaglomerular apparatus increases renin secretion, causing hypertension. Although the association between stone formation and hypertension is well established, the molecular mechanism linking these pathophysiologies has been elusive.

METHODS

To investigate the relationship between succinate and citrate/oxalate levels, we assessed blood and urine levels of metabolites, renal protein expression, and BP (using 24-hour telemetric monitoring) in male mice lacking slc26a6 (a transporter that inhibits the succinate transporter NaDC-1 to control citrate absorption from the urinary lumen). We also explored the mechanism underlying this metabolic association, using coimmunoprecipitation, electrophysiologic measurements, and flux assays to study protein interaction and transport activity.

RESULTS

Compared with control mice, slc26a6^-/- mice (previously shown to have low urinary citrate and to develop calcium oxalate stones) had a 40% decrease in urinary excretion of succinate, a 35% increase in serum succinate, and elevated plasma renin. Slc26a6^-/- mice also showed activity-dependent hypertension that was unaffected by dietary salt intake. Structural modeling, confirmed by mutational analysis, identified slc26a6 and NaDC-1 residues that interact and mediate slc26a6's inhibition of NaDC-1. This interaction is regulated by the scaffolding protein IRBIT, which is released by stimulation of the succinate receptor SUCNR1 and interacts with the NaDC-1/slc26a6 complex to inhibit succinate transport by NaDC-1.

CONCLUSIONS

These findings reveal a succinate/citrate homeostatic pathway regulated by IRBIT that affects BP and biochemical risk of calcium oxalate stone formation, thus providing a potential molecular link between hypertension and lithogenesis.

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.

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 acid load and risk of type 2 diabetes: A systematic review and dose-response meta-analysis of prospective observational studies

BACKGROUND & AIMS

Existing evidence suggests a link between acid-forming potential of diet and type 2 diabetes. But the degree of the associations and shape of the dose-response relations across different indices of diet-dependent acid load and risk of type 2 diabetes and potential confounding by sex have not been established. We aimed to test the dose-response association of different measures of dietary acid load and risk of incident type 2 diabetes, with considering the sex as a potential confounder.

METHODS

Systematic search was done using PubMed and Scopus, from inception up to September 2017. Prospective observational studies reporting the risk estimates of type 2 diabetes for three or more quantitative categories of potential renal acid load (PRAL), net endogenous acid production (NEAP) and animal protein-to-potassium ratio (A:P) scores were included. Pooled relative risks (RRs) were calculated using random effects models.

RESULTS

Seven prospective cohort studies with 319,542 participants and 17,986 incident cases of type 2 diabetes were included. Pooled RRs for a 5 unit increment in dietary PRAL, NEAP and A:P was 1.04 (95% CI: 1.01, 1.06; I² = 79%, n = 7), 1.03 (95% CI: 1.01, 1.04; I² = 54%, n = 7), and 1.11 (95% CI: 1.07, 1.15; I² = 41%, n = 3), respectively. Subgroup analysis resulted in significant positive relationship only among women, compared with men. There was a linear association between NEAP and A:P scores and risk of type 2 diabetes, whereas the association appeared to be U-shaped in analysis of PRAL.

CONCLUSIONS

Adherence to a diet with high acid-forming potential might increase the risk of type 2 diabetes. Shape of the dose-response relations across different indices of dietary acid load and potential sex differences in the associations need to be further explored. The interpretation of the results is limited by low number of studies.

Higher dietary acid load is weakly associated with higher adiposity measures and blood pressure in Japanese adults: The National Health and Nutrition Survey

Epidemiologic evidence on the associations between dietary acid load and metabolic risk factors are limited and inconsistent. We investigated the hypothesis that dietary acid load is associated with adverse profiles of metabolic risk factors in Japanese adults. This cross-sectional study included 15 618 Japanese adults aged ≥20 years from the 2012 National Health and Nutrition Survey, Japan. Dietary acid load was characterized as potential renal acid load (PRAL) and net endogenous acid production (NEAP) based on information on nutrient intake, which was derived from a 1-day semi-weighed dietary record. After adjustment for potential confounding factors, both PRAL and NEAP were positively associated with body mass index (BMI) and waist circumference in both sexes (P for trend ≤.01). PRAL and NEAP also showed positive associations with systolic and diastolic blood pressure in men, independently of BMI (P for trend ≤.005), while they showed positive associations with systolic (but not diastolic) blood pressure in women (P for trend ≤.03). For other metabolic risk factors, there were positive associations between PRAL and NEAP and total and LDL-cholesterol concentrations only in men (P for trend ≤.04). After excluding participants taking medication for hypertension, dyslipidemia, and diabetes, similar associations were observed for adiposity measures and blood pressure (P for trend ≤.01), with there being positive associations between NEAP and HDL-cholesterol and between PRAL and NEAP and glycated hemoglobin in men (P for trend ≤.04). In conclusion, higher dietary acid load was significantly but weakly associated with higher adiposity measures and blood pressure in Japanese adults.

Risk of Hypertension among First-Time Symptomatic Kidney Stone Formers

BACKGROUND AND OBJECTIVES

Prior work has suggested a higher risk of hypertension in kidney stone formers but lacked disease validation and adjustment for potential confounders. Certain types of stone formers may also be at higher risk of hypertension.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In our study, incident symptomatic stone formers in Olmsted County from 2000 to 2011 were manually validated by chart review and age and sex matched to Olmsted County controls. We followed up patients through November 20, 2015. Hypertension was also validated by manual chart review, and the risk of hypertension in stone formers compared with controls was assessed both univariately and after adjusting for comorbidities. The risk of hypertension among different subtypes of stone formers was also evaluated.

RESULTS

Among 3023 coded stone formers from 2000 to 2011, a total of 1515 were validated and matched to 1515 controls (mean age was 45 years old, and 56% were men). After excluding those with baseline hypertension (20% of stone formers and 18% of controls), 154 stone formers and 110 controls developed hypertension. Median follow-up time was 7.8 years in stone formers and 9.6 years in controls. Stone formers were found to have a higher risk of hypertension compared with controls (hazard ratio, 1.50; 95% confidence interval, 1.18 to 1.92), even after adjusting for age, sex, body mass index, serum creatinine, CKD, diabetes, gout, coronary artery disease, dyslipidemia, tobacco use, and alcohol abuse (hazard ratio, 1.58; 95% confidence interval, 1.12 to 2.21). Results were similar after excluding patients who were ever on a thiazide diuretic (hazard ratio, 1.65; 95% confidence interval, 1.16 to 2.38). Stone composition, radiographic stone burden, number of subsequent stone events, and stone removal surgeries were not associated with hypertension (P>0.05 for all).

CONCLUSIONS

The risk of hypertension was higher after the first symptomatic kidney stone event. However, kidney stone severity, type, and treatment did not associate with hypertension.

The association of nephrolithiasis with metabolic syndrome and its components: a cross-sectional analysis

Background

Metabolic syndrome is a worldwide disorder and also the major risk factor of several systemic diseases. Evidence identifying the association between metabolic syndrome and nephrolithiasis is lacking, especially in Taiwan.

Aim

The aim of this study was to investigate the association between nephrolithiasis and metabolic syndrome and its components.

Design and setting

This was a cross-sectional study conducted in the Health Examination Department of a medical center in Changhua, Taiwan, from January 2010 to December 2010.

Methods

We reviewed the medical records of patients who had visited the Health Examination Center of Changhua Christian Hospital in 2010. A total of 3,886 individuals were enrolled. According to the exclusion criteria, those with an age <20 years and an abnormal renal function were excluded. A total of 3,793 subjects were included. All P-values are two tailed, and P<0.05 was defined as statistically significant.

Results

The results showed a correlation between nephrolithiasis and metabolic syndrome and its components. The multivariate-adjusted odds ratio (OR) (95% confidence interval [CI]) of metabolic syndrome for nephrolithiasis was 1.318 (1.083–1.604), with a P-value of 0.006. Larger waist circumference (multivariable-adjusted OR 1.338; 95% CI 1.098–1.631; P=0.004), higher blood pressure (multivariable-adjusted OR 1.333; 95% CI 1.106–1.607; P=0.003), and increased fasting glucose (multivariable-adjusted OR 1.276; 95% CI 1.054–1.546; P=0.01) were associated with nephrolithiasis.

Conclusion

This is the first study in Taiwan to investigate the relationship between metabolic syndrome and nephrolithiasis. The mechanism is controversial, and several hypotheses are offered. Adequate lifestyle modification and proper treatment in metabolic syndrome management may both contribute to nephrolithiasis prevention.

Systemic implications of urinary stone disease

Urinary stone disease is the third most common condition affecting the urinary tract. It contributes to a great deal of morbidity for both men and women, and cost the United States (US) over 5.3 billion dollars in 2000 alone. Moreover, it is associated with systemic diseases such as hypertension, diabetes, and other components of the metabolic syndrome. Reciprocally, these systemic diseases may be contributing to the rising incidence in urinary stone disease. Previously described mechanisms of stone formation attribute stone development and growth to the urinary milieu. While this may partly influence the process, it cannot account for the associations between systemic diseases and stones observed in large community-based studies. Here we present a review of the evidence demonstrating a link between urinary stone disease and components of the metabolic syndrome. We believe a vascular etiology for the initiation of urinary stones may tie these processes together.

Does hypertension impact 24-hour urine parameters in patients with nephrolithiasis?

OBJECTIVE

To examine the differences in 24-hour urine parameters and stone composition between patients with and without systemic hypertension (HTN) in a large cohort of stone formers.

MATERIALS AND METHODS

We performed a retrospective review over a 10-year period of patients with stone, who had completed a 24-hour urinalysis (Litholink) and for whom demographic information was available, including the presence of HTN. Univariate and multivariate analyses were performed, comparing the 24-hour urinalysis profiles of patients with HTN with that of normotensive patients.

RESULTS

Of the 1115 patients eligible for inclusion, 442 patients (40%) had HTN and 673 (60%) did not. Patients with HTN were significantly older, had a higher body mass index, and had a greater number of comorbid conditions than normotensive patients. Univariate analysis revealed significantly lower urine pH, calcium, supersaturation (SS) of calcium oxalate (CaOx) and SS calcium phosphate (all P <.05) in patients with HTN. Multivariate analysis showed significantly lower calcium, citrate, and SS CaOx in patients with HTN (all P <.05).

CONCLUSION

Our results demonstrate lower levels of calcium and SS CaOx on univariate and multivariate analysis, as well as lower levels of citrate on multivariate analysis in patients with HTN. These results suggest that lower levels of citrate may contribute to stone formation to a greater degree in patients with HTN than abnormalities in calcium metabolism.

Lower vegetable protein intake and higher dietary acid load associated with lower carbohydrate intake are risk factors for metabolic syndrome in patients with type 2 diabetes: Post-hoc analysis of a cross-sectional study

Aims/Introduction

A low-carbohydrate diet based on animal sources is associated with higher all-cause mortality, whereas a vegetable-based low-carbohydrate diet is associated with lower cardiovascular disease mortality. It has been suggested that acid/base imbalance might play an important role in some cardiometabolic abnormalities. The aims of the present study were to evaluate whether carbohydrate intake is associated with quality of dietary protein and acid load, and whether these are related to metabolic syndrome in patients with type 2 diabetes.

Materials and Methods

The present cross-sectional study involved 149 patients with type 2 diabetes. Dietary intake was assessed using a validated self-administered diet history questionnaire. Dietary acid load was assessed by potential renal acid load and net endogenous acid production.

Results

Mean daily total energy intake, carbohydrate intake, animal protein intake and vegetable protein intake were 1821.5 kcal, 248.8 g, 36.1 g and 31.1 g, respectively. Carbohydrate energy/total energy was negatively correlated with animal protein energy/total energy, potential renal acid load or net endogenous acid production score, and was positively correlated with vegetable protein energy/total energy. Logistic regression analyses showed that the subgroup of patients with a lower vegetable protein energy/total energy or higher potential renal acid load or net endogenous acid production score was significantly associated with the prevalence of metabolic syndrome.

Conclusions

The present study showed that carbohydrate intake was associated with the quality of dietary protein and dietary acid load. Furthermore, decreased vegetable protein intake and increased dietary acid load were associated with the prevalence of metabolic syndrome.

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.

High dietary acid load is associated with increased prevalence of hypertension: the Furukawa Nutrition and Health Study

OBJECTIVE

Acid-base status has been suggested to influence blood pressure, but there is a paucity of epidemiologic evidence linking dietary acid load to hypertension. We examined cross-sectionally the association between dietary acid load and hypertension in a Japanese working population.

METHODS

Data were derived from health surveys from 2028 employees, ages 18 to 70 y, in two workplaces in Japan. A validated brief diet history questionnaire was used to assess diet. Two measures were used to characterize dietary acid load: potential renal acid load and estimated net endogenous acid production, which were derived from nutrient intakes. Multilevel logistic regression was used to examine the association between dietary acid load and hypertension with adjustment of potential confounding variables.

RESULTS

High dietary acid load was suggestively associated with increased prevalence of hypertension. The multivariable adjusted odds ratios (95% confidence interval) of hypertension for the lowest through highest tertiles of net endogenous acid production were 1.00 (reference), 1.07 (0.80-1.42), and 1.33 (0.998-1.78), respectively (P for trend = 0.053). This positive association was statistically significant among normal-weight (body mass index <23 kg/m(2); P for trend = 0.03) and non-shift workers (P for trend = 0.04). Similar positive associations were observed between potential renal acid load and hypertension.

CONCLUSIONS

The present findings suggest that high dietary acid load may be associated with increased prevalence of hypertension among those who were normal weight and non-shift workers.

Hypertriglyceridemia and low high-density lipoprotein cholesterolemia are associated with increased hazard for urolithiasis

PURPOSE

To assess the association between dyslipidemia and urolithiasis, a propensity score-matching study was performed.

PATIENTS AND METHODS

Fasting blood samples were taken, and serum lipid profiles were measured in 655 stone formers (SF) and 1965 propensity score-matched controls between 2005 and 2011. The controls, from a health-screening program, did not have a history of dyslipidemia or statin use and have any evidence of stone disease, as determined by abdominal radiography, ultrasonography examination. Propensity score-matching with respect to age, sex, and body mass index was used to minimize selection bias, and the logistic regression analysis was adjusted for other components of metabolic syndrome.

RESULTS

Compared with controls, the SF group had significantly higher mean triglyceride and lower total cholesterol, low-density lipoprotein (LDL) cholesterol, and high-density lipoprotein (HDL) cholesterol levels (each P<0.001). The SF group was also more likely to have hypertriglyceridemia and low HDL-cholesterolemia, and less likely to have hypercholesterolemia and high LDL cholesterolemia compared with controls (each P<0.05). When adjusted for other components of metabolic syndrome including obesity, presence of diabetes mellitus or hypertension, the odds ratio (OR) for urinary stones appeared with hypercholesterolemia (OR=0.747, P=0.003), hypertriglyceridemia (OR=1.901, P<0.001), low HDL cholesterolemia (OR=1.886, P<0.001) and high LDL cholesterolemia (OR=0.610, P<0.001).

CONCLUSIONS

Our study implies that dyslipidemia may play a crucial part in urinary stone risk.

Plasma bicarbonate and odds of incident hypertension

BACKGROUND

Several biomarkers of metabolic acidosis, including lower plasma bicarbonate, have been associated with prevalent hypertension in cross-sectional studies. We sought to examine prospectively whether lower plasma bicarbonate is associated with incident hypertension.

METHODS

We conducted a prospective case-control study nested within the Nurses' Health Study II. Plasma bicarbonate was measured in 695 nonobese women without hypertension at time of blood draw who subsequently developed hypertension during 6 years of follow-up. Control subjects were matched to case subjects according to age, race, time and day of blood draw, and day of menstrual cycle. We used unconditional logistic regression to generate odds ratios (ORs) for development of hypertension by quintile of baseline plasma bicarbonate.

RESULTS

After adjusting for matching factors, body mass index, family history of hypertension, plasma creatinine, and dietary and lifestyle factors, higher plasma bicarbonate was associated with lower odds of developing hypertension across quintiles (P for linear trend = 0.04). Those in the highest compared with the lowest quintile of plasma bicarbonate had 31% lower odds of developing hypertension (OR = 0.69; 95% confidence interval = 0.48-0.99). Further adjustment for diet-estimated net endogenous acid production, plasma insulin, 25-hydroxyvitamin D, and uric acid did not alter these findings.

CONCLUSIONS

Our case-control study is consistent with a modest association between higher plasma bicarbonate and reduced odds of developing hypertension among nonobese women, although our findings are of borderline statistical significance. Further research is required to confirm this finding as part of a larger prospective cohort study and to elucidate the mechanism for this relation.

The association of prevalent kidney stone disease with mortality in US adults: the National Health and Nutrition Examination Survey III, 1988-1994

BACKGROUND

Kidney stone disease is associated with hypertension, diabetes, metabolic syndrome, kidney function decline, and increased cardiovascular (CV) events. However, its association with all-cause and CV mortality is unclear.

METHODS

We used the Third National Health and Nutrition Examination Survey, a large US population-based study with mortality data through 2006 determined via linkage to the National Death Index to examine kidney stone disease in relation to all-cause and CV mortality risks.

RESULTS

Among 14,879 men and women over 18 years of age who were eligible for analysis, 683 participants reported a history of kidney stones. There was a total of 3,590 all-cause and 1,608 CV deaths during a median follow-up of 14.9 years. Stone formers had a significantly higher risk for all-cause mortality [hazard ratio (HR): 1.95, 95% CI: 1.64-2.33, p < 0.0001) and CV mortality (HR: 2.05, 95% CI: 1.60-2.62, p < 0.0001) in unadjusted analyses. However, after multivariate adjustment for age, gender, race, and poverty, stone formers no longer had increased risk for all-cause mortality (HR: 1.08, 95% CI: 0.93-1.26, p = 0.3) and CV mortality (HR: 1.07, 95% CI: 0.84-1.36, p = 0.6). Results remain unchanged after further adjustment for other clinical variables including history of hypertension, diabetes, and CV disease.

CONCLUSION

The increased risk of all-cause and CV mortality in kidney stone formers is likely a reflection of unique demographics and associated comorbidities. There is no independent association of prevalent kidney stone disease with all-cause and CV mortality.

Dietary and lifestyle factors and medical conditions associated with urinary citrate excretion

BACKGROUND AND OBJECTIVES

Lower urinary citrate excretion is a risk factor for nephrolithiasis and associated with metabolic acidosis and higher prevalence of hypertension and insulin resistance. This study sought to quantify the independent predictors of urinary citrate excretion in population-based cohorts.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

A cross-sectional study of 2561 individuals from the Health Professionals Follow-Up Study and Nurses' Health Studies I and II who provided two 24-hour urine collections was conducted. Dietary data were ascertained from the semiquantitative food frequency questionnaire. Lifestyle and disease data were derived from responses to biennial questionnaires. Multivariable linear regression was used to quantify the predictors of urinary citrate excretion.

RESULTS

After adjusting for age, urinary creatinine, dietary, and other factors, higher intake of nondairy animal protein (per 10 g/d; -20 mg/d; 95% confidence interval [-29 to -11]), higher body mass index (per 1 kg/m(2); -4 mg/d; [-6 to -2]), and history of nephrolithiasis (-57 mg/d; [-79 to -36]), hypertension (-95 mg/d; [-119 to -71]), gout (-104 mg/d; [-155 to -54]), and thiazide use (-34 mg/d; [-68 to -1]) were independently associated with lower 24-hour urinary citrate excretion. Higher intake of potassium (per 1000 mg/d; 53 mg/d; [33 to 74]), higher urinary sodium (per 100 mEq/d; 56 mg/d; [31 to 80]), and history of diabetes (61 mg/d; [21 to 100]) were independently associated with higher citrate excretion.

CONCLUSIONS

Several dietary and lifestyle factors and medical conditions are independently associated with urinary citrate excretion.

Association of metabolic syndrome traits and severity of kidney stones: results from a nationwide survey on urolithiasis in Japan

BACKGROUND

Although metabolic syndrome and its individual components have been associated with kidney stone disease, whether the clustering of metabolic syndrome traits increases the severity of kidney stone disease has not been examined in a large-scale study.

STUDY DESIGN

Cross-sectional analysis.

SETTING & PARTICIPANTS

Data were obtained from 30,448 patients enrolled in the 6th Nationwide Survey on Urolithiasis in Japan conducted in 2005. Patients with lower urinary tract stones, struvite stones, cystine stones, or hyperparathyroidism and those younger than 15 years were excluded.

PREDICTOR

Number of metabolic syndrome traits (obesity [body mass index ≥25 kg/m(2)], diabetes, hypertension, and dyslipidemia).

OUTCOMES

Severe form of kidney stone disease, defined as recurrent and/or multiple stones, and abnormalities in urine constituents (hypercalciuria, hyperuricosuria, hyperoxaluria, and hypocitraturia).

RESULTS

11,555 patients were included in the final analyses. Proportions of patients with recurrent and/or multiple stones were 57.7%, 61.7%, 65.2%, 69.3%, and 73.3% with 0, 1, 2, 3, and 4 metabolic syndrome traits, respectively (P < 0.001). There was a significant and stepwise increase in the odds of recurrent and/or multiple stones after adjustment for age and sex. In patients with 4 metabolic syndrome traits, the odds was 1.8-fold greater compared with patients with 0 traits (OR, 1.78; 95% CI, 1.22-2.66). In addition, the presence of metabolic syndrome traits was associated with significantly increased odds of having hypercalciuria, hyperuricosuria, hyperoxaluria, and hypocitraturia after adjustment for age and sex.

LIMITATIONS

Cross-sectional design, absence of dietary data, ill-defined diagnostic criteria for metabolic syndrome traits, and missing data for the majority of participants.

CONCLUSIONS

Metabolic syndrome trait clustering is associated with greater severity of kidney stone disease; increased urinary calcium, uric acid, and oxalate excretion; and decreased urinary citrate excretion. These results suggest that kidney stone disease should be regarded as a systemic disorder linked to metabolic syndrome.

New insights into the pathogenesis of renal calculi

The pathophysiology of the various forms of urinary stone disease remains a complex topic. Epidemiologic research and the study of urine and serum chemistries have created an abundance of data to help drive the formulation of pathophysiologic theories. This article addresses the associations of urinary stone disease with hypertension, cardiovascular disease, atherosclerosis, obesity, dyslipidemia, diabetes, and other disease states. Findings regarding the impact of dietary calcium and the formation of Randall's plaques are also explored and their implications discussed. Finally, further avenues of research are explored, including genetic analyses and the use of animal models of urinary stone disease.

Association between body mass index, lipid profiles, and types of urinary stones

OBJECTIVE

The purpose of this study was to determine the differences in body mass index (BMI), levels of cholesterol, and levels of triglycerides (TGs) among urolithiasis patients with different stone compositions.

MATERIALS AND METHODS

Forty-nine patients who had a diagnosis of nephrolithiasis and had undergone open surgery or percutaneous surgery were included, and patients without urolithiasis were randomly selected as controls. Urinary stones were collected and analyzed using infrared spectroscopy. Data relating to patient's age, BMI at diagnosis, serum total cholesterol (TC), high-density lipoprotein cholesterol, and low-density lipoprotein cholesterol (LDL-C) were collected. The stone groups including calcium oxalate monohydrate-calcium oxalate dihydrate (COM-COD), COM, and uric acid were compared with one another and with the control group. In addition, the stone formers group (COM-COD, COM, uric acid, calcium phosphate, and mixed-type stones) was compared to the control group.

RESULTS

BMI, TC, and TG levels were significantly higher in stone formers compared with the control group; this association of BMI and TC with stone formation was more prominent in uric acid and COM-COD stone formers, but there was no such prominence for COM stones. LDL-C levels in COM-COD stone formers were significantly higher when compared with COM stone formers.

CONCLUSION

Elevated BMI, hypercholesterolemia, and hyperlipidemia, which are leading components of metabolic syndrome, may be associated with different types of urinary stone formation.

Metabolic syndrome and urinary stone composition: what factors matter most?

OBJECTIVE

To determine which metabolic syndrome (MetS) factors lead to differences in stone composition in a multivariate analysis.

METHODS

We retrospectively reviewed medical charts of patients who had a kidney stone removed over a 5-year period (2006-2011). MetS factors (obesity [body mass index {BMI} >30], diabetes mellitus [DM], hypertension [HTN], and dyslipidemia [DLD]) were tallied in each patient. For the latter 3 factors, medical treatment for the condition was used to tag a patient with the condition. Stone composition was determined by the dominant (>50%) component. Statistical analysis was designed to determine which MetS factors were independently associated with differences in stone composition.

RESULTS

Five hundred ninety kidney stones were included in the analysis. Patients with MetS had a higher prevalence of uric acid stones and lower prevalence of calcium phosphate stones. HTN and DM were independently associated with differences in composition, specifically uric acid stones (higher proportion), and calcium phosphate stones (lower proportion). Obesity was not associated with differences in composition, although a secondary analysis of morbidly obese patients showed a higher proportion of uric acid stones and a lower proportion of calcium oxalate stones.

CONCLUSION

HTN and DM are the MetS factors independently associated with differences in stone composition, specifically the uric acid and calcium phosphate components. Obesity has little effect on stone composition until a very high (>40) BMI is reached. The overall effect of MetS factors on stone type is relatively small, because most stones are calcium oxalate and MetS factors have little impact on calcium oxalate frequency.

Dietary acid load and risk of hypertension: the Rotterdam Study

BACKGROUND

Mild metabolic acidosis, which can be caused by diet, may result in elevated blood pressure (BP).

DESIGN

The analyses included 2241 participants aged ≥55 y who were free of hypertension at baseline (1990-1993) and who had complete dietary and BP data. Dietary data were obtained from a 170-item food-frequency questionnaire. We used 2 measures to characterize dietary acid load: (1) potential renal acid load (PRAL) by using an algorithm including protein, phosphorus, potassium, calcium, and magnesium, and (2) estimated net endogenous acid production (NEAP) based on protein and potassium. HRs for 6-y incidence of hypertension were obtained in tertiles of PRAL and NEAP with adjustment for age, sex, BMI, smoking, education, and intakes of alcohol, fiber, and total energy.

RESULTS

We identified 1113 incident cases of hypertension during 8707 person-years of follow-up. The median dietary acid load ranged from -14.6 to 19.9 mEq/d across categories of PRAL. Hypertension risk was not significantly associated with dietary acid load. The multivariate HRs (95% CIs) in consecutive tertiles of PRAL were 1.00 (reference), 1.01 (0.87, 1.17), and 1.02 (0.88, 1.18) (P trend = 0.83). The median dietary acid loads were 30.4, 36.7, and 43.7 mEq/d, respectively, in consecutive tertiles of NEAP. Corresponding HRs for NEAP were 1.00 (reference), 0.92 (0.80, 1.07), and 0.94 (0.81, 1.10) (P-trend = 0.46).

CONCLUSION

The findings from this prospective cohort study provided no evidence of an association between dietary acid load and risk of hypertension in older adults.

The association of cardiovascular disease and metabolic syndrome with nephrolithiasis

PURPOSE OF REVIEW

This review describes the relationship between nephrolithiasis, vascular disease and metabolic syndrome.

RECENT FINDINGS

There is increasing evidence that kidney stone formation is associated with a number of systemic problems including cardiovascular disease, metabolic syndrome and its components. Some of these associations are bidirectional. The reasons for these associations are not totally clear, but potential factors include metabolic responses associated with these disorders that promote a stone forming milieu in urine, environmental factors such as diet, oxidative stress and inflammation and molecular changes impacting the transport of certain analytes in urine.

SUMMARY

Urologists need to be cognizant of these associations as they may be able to contribute to an early diagnosis of a significant medical problem, or provide counseling to patients to prevent their occurrence.

Is oxidative stress, a link between nephrolithiasis and obesity, hypertension, diabetes, chronic kidney disease, metabolic syndrome?

Epidemiological studies have provided the evidence for association between nephrolithiasis and a number of cardiovascular diseases including hypertension, diabetes, chronic kidney disease, metabolic syndrome. Many of the co-morbidities may not only lead to stone disease but also be triggered by it. Nephrolithiasis is a risk factor for development of hypertension and have higher prevalence of diabetes mellitus and some hypertensive and diabetic patients are at greater risk for stone formation. An analysis of the association between stone disease and other simultaneously appearing disorders, as well as factors involved in their pathogenesis, may provide an insight into stone formation and improved therapies for stone recurrence and prevention. It is our hypothesis that association between stone formation and development of co-morbidities is a result of certain common pathological features. Review of the recent literature indicates that production of reactive oxygen species (ROS) and development of oxidative stress (OS) may be such a common pathway. OS is a common feature of all cardiovascular diseases (CVD) including hypertension, diabetes mellitus, atherosclerosis and myocardial infarct. There is increasing evidence that ROS are also produced during idiopathic calcium oxalate (CaOx) nephrolithiasis. Both tissue culture and animal model studies demonstrate that ROS are produced during interaction between CaOx/calcium phosphate (CaP) crystals and renal epithelial cells. Clinical studies have also provided evidence for the development of oxidative stress in the kidneys of stone forming patients. Renal disorders which lead to OS appear to be a continuum. Stress produced by one disorder may trigger the other under the right circumstances.

A metabonomic study of biochemical changes characteristic of genetically hypertensive rats based on (1)H NMR spectroscopic urinalysis

Spontaneously hypertensive rats (SHR) provide a simple model for studying essential hypertension. Their genetic and metabolic features are of great interest because they may provide insights into the pathophysiological processes underlying essential hypertension. We have thus investigated the metabolic characteristics of SHR at various ages, covering the prehypertensive stage and the developmental phase of hypertension, using a (1)H nuclear magnetic resonance (NMR)-based metabonomic approach. Twenty-four-hour urine samples from the SHR and their age-matched normotensive control, Wistar-Kyoto rats, were analyzed using (1)H NMR spectroscopy, and the spectral data were subjected to principal components analysis (PCA) to find metabolic differences between the two strains. Consequently, it was possible to separate the urine samples between the two strains at any age ranging from 4 to 20 weeks in the principal component scores plots. The major spectral regions and signals (metabolites) contributing to the separation were picked up based on the loadings. Subsequently, the urinary excreted levels of metabolites highlighted by the PCA were compared based on the signal intensities corrected by urine volume and body weight. These investigations revealed the major metabolic changes characteristic of the SHR, which included differences in citrate, α-ketoglutarate, succinate, hippurate, phenylacetylglycine, p-cresol glucuronide, creatine, taurine, medium-chain dicarboxylates (tentative), unknown (δ 3.11), and the regions at 3.60, 3.64, 3.68 and 3.88 p.p.m. The results supported the occurrence of metabolic acidosis in the SHR in the period of prehypertension as well as rapidly rising blood pressure. In addition, the intestinal microfloral populations in the SHR were suggested to be altered in the developmental phase of hypertension.

The relationship of obesity and gender prevalence changes in United States inpatient nephrolithiasis

OBJECTIVE

To review the Nationwide Inpatient Sample database to examine the relationships between obesity, gender, and nephrolithiasis. Recent reports indicate that the prevalence of nephrolithiasis has been increasing, especially among women.

METHODS

The Nationwide Inpatient Sample contains data on approximately 20% of hospital stays in the United States. Included in this analysis were discharges with primary diagnosis ICD-9 codes 592.0 (renal calculus) or 592.1 (ureteral calculus), from 1998 through 2003. All raw data were weighted to produce national estimates. Descriptive and inferential statistics were performed to determine changes in nephrolithiasis prevalence and associations of obesity and other comorbidities with nephrolithiasis.

RESULTS

We reviewed 181,092,957 hospital stays (weighted data). The prevalence of nephrolithiasis was relatively stable: 0.52% (149,302) in 1998 and 0.47% (147,541) in 2003. The prevalence of obesity increased from 3.06% (878,155) to 4.99% (1,575,247). The male:female ratio of patients with stones decreased from 1.6:1 to 1.2:1. Multivariate analysis revealed a statistically significant relationship (OR = 1.22, 95% CI 1.20-1.23, P <.001) between obesity and urinary stones. Obese females were more likely to develop stones than nonobese females (OR = 1.35, 95% CI 1.33-1.37, P <.001). The association between obesity and stones was weaker in males (OR = 1.04, 95% CI 1.02-1.06, P <.001).

CONCLUSION

In this sample of inpatients, obesity was associated with a significantly increased prevalence of urinary stones. This relationship was stronger in females than in males. Further studies are needed to determine whether weight reduction in obese patients affects urinary stone disease.

Association between metabolic syndrome and the presence of kidney stones in a screened population

BACKGROUND

Components of metabolic syndrome have been associated with kidney stone disease, but little evidence is available to support a relationship between metabolic syndrome and kidney stone development in healthy large screened populations.

STUDY DESIGN

Cross-sectional analysis.

SETTING & PARTICIPANTS

Data were obtained from 34,895 individuals who underwent general health screening tests between January 2006 and December 2006 at the Asan Medical Center.

PREDICTOR

Metabolic syndrome was defined according to criteria established by the National Cholesterol Education Program Adult Treatment Panel III, American Heart Association, and National Heart, Lung, and Blood Institute.

OUTCOMES & MEASUREMENTS

The presence of kidney stones was evaluated using computed tomography or ultrasonography.

RESULTS

Of all those screened, 839 (2.4%) had radiologic evidence of kidney stones and metabolic syndrome was diagnosed in 4,779 (13.7%). The multivariable-adjusted OR for kidney stones increased with an increasing quintile of waist circumference and systolic/diastolic blood pressure (P < 0.001). Age, sex, hypertension, and metabolic syndrome status were independent risk factors for kidney stones. The presence of metabolic syndrome had an OR of 1.25 (95% CI, 1.03-1.50) for kidney stone prevalence. In participants with hypertension, the OR for the presence of kidney stones was 1.47 (95% CI, 1.25-1.71) compared with that for participants without hypertension after adjustment for other variables.

LIMITATIONS

Cross-sectional design, absence of stone composition.

CONCLUSION

Metabolic syndrome is associated with a significantly increased risk of kidney stone development. Our findings suggest the need for interventional studies to test the effects of preventing and treating metabolic syndrome on the risk of kidney stone development.

Diet-induced metabolic acidosis

The modern Western-type diet is deficient in fruits and vegetables and contains excessive animal products, generating the accumulation of non-metabolizable anions and a lifespan state of overlooked metabolic acidosis, whose magnitude increases progressively with aging due to the physiological decline in kidney function. In response to this state of diet-derived metabolic acidosis, the kidney implements compensating mechanisms aimed to restore the acid-base balance, such as the removal of the non-metabolizable anions, the conservation of citrate, and the enhancement of kidney ammoniagenesis and urinary excretion of ammonium ions. These adaptive processes lower the urine pH and induce an extensive change in urine composition, including hypocitraturia, hypercalciuria, and nitrogen and phosphate wasting. Low urine pH predisposes to uric acid stone formation. Hypocitraturia and hypercalciuria are risk factors for calcium stone disease. Even a very mild degree of metabolic acidosis induces skeletal muscle resistance to the insulin action and dietary acid load may be an important variable in predicting the metabolic abnormalities and the cardiovascular risk of the general population, the overweight and obese persons, and other patient populations including diabetes and chronic kidney failure. High dietary acid load is more likely to result in diabetes and systemic hypertension and may increase the cardiovascular risk. Results of recent observational studies confirm an association between insulin resistance and metabolic acidosis markers, including low serum bicarbonate, high serum anion gap, hypocitraturia, and low urine pH.

Metabolic acidosis-induced insulin resistance and cardiovascular risk

Microalbuminuria has been conclusively established as an independent cardiovascular risk factor, and there is evidence of an association between insulin resistance and microalbuminuria, the former preceding the latter in prospective studies. It has been demonstrated that even the slightest degree of metabolic acidosis produces insulin resistance in healthy humans. Many recent epidemiological studies link metabolic acidosis indicators with insulin resistance and systemic hypertension. The strongly acidogenic diet consumed in developed countries produces a lifetime acidotic state, exacerbated by excess body weight and aging, which may result in insulin resistance, metabolic syndrome, and type 2 diabetes, contributing to cardiovascular risk, along with genetic causes, lack of physical exercise, and other factors. Elevated fruits and vegetables consumption has been associated with lower diabetes incidence. Diseases featuring severe atheromatosis and elevated cardiovascular risk, such as diabetes mellitus and chronic kidney failure, are typically characterized by a chronic state of metabolic acidosis. Diabetic patients consume particularly acidogenic diets, and deficiency of insulin action generates ketone bodies, creating a baseline state of metabolic acidosis worsened by inadequate metabolic control, which creates a vicious circle by inducing insulin resistance. Even very slight levels of chronic kidney insufficiency are associated with increased cardiovascular risk, which may be explained at least in part by deficient acid excretory capacity of the kidney and consequent metabolic acidosis-induced insulin resistance.

Kidney stones and subclinical atherosclerosis in young adults: the CARDIA study

PURPOSE

Recent reports suggest that nephrolithiasis and atherosclerosis share a number of risk factors. To our knowledge there has been no previous examination of the relationship between kidney stones and subclinical atherosclerotic disease. We studied the relationship between nephrolithiasis, and carotid wall thickness and carotid stenosis assessed by B-mode ultrasound in the general community using data from the CARDIA study.

MATERIALS AND METHODS

The CARDIA study is a United States, population based, observational study of 5,115 white and African-American men and women between the ages of 18 and 30 years at recruitment in 1985 to 1986.

RESULTS

By the year 20 examination 200 (3.9%) CARDIA participants had reported ever having kidney stones. Symptomatic kidney stones were associated with greater carotid wall thickness measured at the year 20 examination, particularly of the internal carotid/bulb region. Using a composite dichotomous end point of carotid stenosis and/or the upper quartile of internal carotid/bulb wall thickness, the association of kidney stones with carotid atherosclerosis was significant (OR 1.6, 95% CI 1.1-2.3, p=0.01), even after adjusting for major atherosclerotic risk factors.

CONCLUSIONS

The association between a history of kidney stones and subclinical carotid atherosclerosis in young adults adds further support to the notion that nephrolithiasis and atherosclerosis share common systemic risk factors and/or pathophysiology.