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Summary It is unclear whether optimal levels of 25-hydroxyvitamin D (25(OH)D) in whites are the same as in minorities. In adult participants of NHANES, the relationships between 25(OH)D, bone mineral density (BMD), and parathyroid hormone (PTH) differed in blacks as compared to whites and Mexican-Americans, suggesting that optimal 25(OH)D levels for bone and mineral metabolism may differ by race. Introduction Blacks and Hispanics have lower 25-hydroxyvitamin D concentrations than whites. However, it is unclear whether 25(OH)D levels considered “optimal” for bone and mineral metabolism in whites are the same as those in minority populations. Methods We examined the relationships between 25(OH)D and parathyroid hormone in 8,415 adult participants (25% black and 24% Mexican-American) in the National Health and Nutrition Examination Surveys 2003–2004 and 2005–2006; and between 25(OH)D and bone mineral density in 4,206 adult participants (24% black and 24% Mexican-American) in the 2003–2004 sample. Results Blacks and Mexican-Americans had significantly lower 25(OH)D and higher PTH concentrations than whites ( P  < 0.01 for both). BMD significantly decreased ( P  < 0.01) as serum 25(OH)D and calcium intake declined among whites and Mexican-Americans, but not among blacks ( P  = 0.2). The impact of vitamin D deficiency (25(OH)D ≤ 20 ng/ml) on PTH levels was modified by race/ethnicity ( P for interaction, 0.001). Whereas inverse relationships between 25(OH)D and PTH were observed above and below a 25(OH)D level of 20 ng/ml in whites and Mexican-Americans, an inverse association between 25(OH)D and PTH was only observed below this threshold in blacks, with the slope of the relationship being essentially flat ( P  = 0.7) above this cut-point, suggesting that PTH may be maximally suppressed at lower 25(OH)D levels in blacks than in whites or Mexican-Americans. Conclusions The relationships between 25(OH)D, BMD, and PTH may differ by race among US adults. Whether race-specific ranges of optimal vitamin D are needed to appropriately evaluate the adequacy of vitamin D stores in minorities requires further study.

There is uncertainty about the relation between 24-h urinary uric acid excretion and the risk of calcium oxalate nephrolithiasis. In addition, the risk associated with different levels of other urinary factors needs clarification. We performed a cross-sectional study of 24-h urine excretion and the risk of kidney stone formation in 3350 men and women, of whom 2237 had a history of nephrolithiasis. After adjusting for other urinary factors, urinary uric acid had a significant inverse association with stone formation in men, a marginal inverse association with risk in younger women, and no association in older women. The risk of stone formation in men and women significantly rose with increasing urine calcium and oxalate, and significantly decreased with increasing citrate and urine volume, with the change in risk beginning below the traditional normal thresholds. Other urinary factors were also associated with risk, but this varied by age and gender. Our study does not support the prevailing belief that higher urine uric acid excretion increases the risk for calcium oxalate stone formation. In addition, the current definitions of normal levels for urinary factors need to be re-evaluated.

Summary Many determinants of parathyroid hormone (PTH) are unknown. In the National Health and Nutrition Examination Survey (NHANES), numerous factors not classically associated with calcium–phosphorus homeostasis, such as uric acid and smoking, are independently associated with PTH in adults without chronic kidney disease. Associations between serum phosphorus and PTH may vary by race. Introduction Although PTH may be an important biomarker for osteoporosis and cardiovascular disease, many determinants of PTH are unknown. We investigated associations between demographic, dietary, and serum factors and PTH level. Methods We studied 4,026 white, 1,792 black, and 1,834 Mexican-American adult participants without chronic kidney disease from the 2003–2004 and 2005–2006 NHANES. Results The mean serum PTH level was 38.3 pg/ml for whites, 42.6 pg/ml for blacks, and 41.3 pg/ml for Mexican-Americans. After adjusting for diet, body mass index, serum levels of calcium, phosphorus, 25-hydroxyvitamin D, creatinine, and other factors, smokers compared to non-smokers had lower PTH, ranging from −4.2 pg/ml (95% confidence interval (CI) −7.3 to −1.1) in Mexican-Americans to −6.1 pg/ml (95% CI −8.7 to −3.5) in blacks. After multivariate adjustment, PTH was higher in females compared to males, ranging from 1.1 pg/ml (95% CI −1.2 to 3.4) in Mexican-Americans to 4.5 pg/ml (95% CI 1.9 to 7.0) in blacks, and in older (>60 years) compared to younger participants (<30 years), ranging from 3.7 pg/ml (95% CI 1.3 to 6.1) in Mexican-Americans to 8.0 pg/ml (95% CI 5.4 to 10.7) in blacks. Higher uric acid was associated with higher PTH. In whites only, lower serum phosphorus and lower serum retinol were associated with higher PTH. Conclusions Numerous factors not classically associated with calcium–phosphorus homeostasis are independently associated with PTH and should be considered in future studies of PTH and chronic disease. Additional research is needed to elucidate mechanisms underlying identified associations with PTH and to explore possible racial differences in phosphorus handling.

Dietary factors play an important role in kidney stone formation, and dietary modification can reduce the risk of stone recurrence. Because stone recurrence rates may be as high as 30–50% after 5 years, individualized dietary intervention to prevent stone recurrence should be offered to every patient willing to participate in a diagnostic work-up and to adhere to treatment recommendations. The necessity of prescribing medical therapy to select patients does not obviate the need for an effective dietary and/or fluid prescription. In this review, we summarize specific dietary and fluid recommendations, and emphasize several key concepts. First, risk factors for stone formation vary by age and sex. Second, recommendations should be tailored to the individual patient based on urinary profile and stone type. Third, it is essential that the patient perform follow-up measurements to evaluate the impact of dietary recommendations. Fourth, it is important to distinguish stone passage from new stone formation. If a patient implements dietary changes and then passes a pre-existing stone, this does not mean that the intervention was not effective. Finally, because of the relative paucity of randomized trials, observational studies provide the basis for many clinical recommendations. Adequate fluid intake and appropriate dietary modifications may substantially reduce the morbidity and costs associated with recurrent nephrolithiasis.

Summary Some recent reports suggest that calcium supplement use may increase risk of cardiovascular disease. In a prospective cohort study of 74,245 women in the Nurses' Health Study with 24 years of follow-up, we found no independent associations between supplemental calcium intake and risk of incident coronary heart disease (CHD) and stroke. Introduction Some recent reports suggest that calcium supplements may increase cardiovascular disease (CVD) risk. The objective was to examine the independent associations between calcium supplement use and risk of CVD. Methods We conducted a prospective cohort study of supplemental calcium use and incident CVD in 74,245 women in the Nurses' Health Study (1984–2008) free of CVD and cancer at baseline. Calcium supplement intake was assessed every 4 years. Outcomes were incident CHD (nonfatal or fatal MI) and stroke (ischemic or hemorrhagic), confirmed by medical record review. Results During 24 years of follow-up, 4,565 cardiovascular events occurred (2,709 CHD and 1,856 strokes). At baseline, women who took calcium supplements had higher levels of physical activity, smoked less, and had lower trans fat intake compared with those who did not take calcium supplements. After multivariable adjustment for age, body mass index, dietary calcium, vitamin D intake, and other CVD risk factors, the relative risk of CVD for women taking >1,000 mg/day of calcium supplements compared with none was 0.82 (95 % confidence interval [CI] 0.74 to 0.92; p for trend <0.001). For women taking >1,000 mg/day of calcium supplements compared with none, the multivariable-adjusted relative risk for CHD was 0.71 (0.61 to 0.83; p for trend < 0.001) and for stroke was 1.03 (0.87 to 1.21; p for trend = 0.61). The relative risks were similar in analyses limited to non-smokers, women without hypertension, and women who had regular physical exams. Conclusions Our findings do not support the hypothesis that calcium supplement intake increases CVD risk in women.

Fructose consumption has markedly increased over the past decades. This intake may increase the urinary excretion of calcium, oxalate, uric acid, and other factors associated with kidney stone risk. We prospectively examined the relationship between fructose intake and incident kidney stones in the Nurses’ Health Study I (NHS I) (93 730 older women), the Nurses’ Health Study II (NHS II) (101 824 younger women), and the Health Professionals Follow-up Study (45 984 men). Food frequency questionnaires were used to assess free fructose and sucrose intake every 4 years. Total-fructose intake was calculated as free fructose plus half the intake of sucrose, and expressed as percentage of total energy. Cox proportional hazard regressions were adjusted for age, body mass index (BMI), thiazide use, caloric intake, and other dietary factors. We documented 4902 incident kidney stones during a combined 48 years of follow-up. The multivariate relative risks of kidney stones significantly increased for participants in the highest compared to the lowest quintile of total-fructose intake for all three study groups. Free-fructose intake was also associated with increased risk. Non-fructose carbohydrates were not associated with increased risk in any cohort. Our study suggests that fructose intake is independently associated with an increased risk of incident kidney stones.

Animal and human data suggest a link between endogenous acid production with elevations in blood pressure and the development of hypertension; increases in endogenous organic acid production can lead to a higher anion gap. We studied the cross-sectional association between the serum anion gap and blood pressure among 1057 non-diabetic patients who were not taking antihypertensive drugs, and who received their care at a multisite, multispecialty group practice in eastern Massachusetts. Using linear regression controlling for age, sex, race, BMI, estimated GFR and presence of impaired fasting glucose, every 1 mEq l(-1) higher serum anion gap was associated with a 0.27 mm Hg (P=0.08) higher systolic, 0.20 mm Hg (P=0.05) higher diastolic and 0.22 mm Hg (P=0.04) higher mean arterial pressure; these results suggest that endogenous acid production may raise the risk of hypertension.

[This corrects the article DOI: 10.1371/journal.pone.0035263.].[This corrects the article DOI: 10.1371/journal.pone.0035263.].

In vitro data suggest that lower extracellular pH activates the immune system. We conducted a population-based study of the relation between serum acid–base status and inflammation. We examined the serum anion gap and serum levels of bicarbonate and inflammatory biomarkers in 4525 healthy adults who participated in the National Health and Nutrition Examination Survey during 1999–2006. We excluded participants who had chronic disease, recent infection and an estimated glomerular filtration rate of less than 60 mL/min per 1.73 m2. The mean values of serum anion gap, bicarbonate level, leukocyte count and C-reactive protein level were all within normal limits. After adjustment for age, sex, ethnic background, body mass index, serum albumin level and other factors, we found that a higher anion gap and lower bicarbonate level were associated with a higher leukocyte count and higher C-reactive protein level. Compared with participants in the lowest quartile of anion gap, those in the highest quartile had a leukocyte count that was 1.0 × 109/L higher and a C-reactive protein level that was 10.9 nmol/L higher (p < 0.01). Compared with participants in the highest quartile of bicarbonate level, those in the lowest quartile had a leukocyte count that was 0.7 × 109/L higher and a C-reactive protein level that was 4.0 nmol/L higher (p ≤ 0.02). A higher anion gap and lower bicarbonate level were also associated with a higher platelet count, a larger mean platelet volume and a higher ferritin level. A higher serum anion gap and lower bicarbonate level were associated with higher levels of inflammatory biomarkers in a healthy sample of the general population. Further studies are needed to elucidate the relation between acid–base status and inflammation.