Demographic, dietary, and serum factors and parathyroid hormone in the National Health and Nutrition Examination Survey.

UNLABELLED: 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.

Racial differences in the relationship between vitamin D, bone mineral density, and parathyroid hormone in the National Health and Nutrition Examination Survey.

UNLABELLED: 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.

Serum bicarbonate, anion gap and insulin resistance in the National Health and Nutrition Examination Survey.

AIMS: Metabolic acidosis may contribute to the development of insulin resistance. To date, there have been no population-based studies of acid-base status and insulin resistance. We examined the cross-sectional relations between serum bicarbonate, anion gap, and insulin resistance in a subset of healthy participants in the 1999-2000 and 2001-2002 National Health and Nutrition Examination Surveys. METHODS: We included 1496 adults without diabetes or other chronic diseases. Insulin sensitivity was estimated by an index based on fasting insulin and triglyceride levels (MFFM). Linear regression was used to adjust for age, race, body mass index, albumin and other factors. Sample weights were used to produce weighted regression parameters. RESULTS: Median values of bicarbonate, anion gap and fasting levels of insulin, triglycerides and glucose were 23 mmol/l, 12.5 mmol/l, 48 pmol/l, 1.08 mmol/l and 5.0 mmol/l, respectively. After multivariable adjustment, bicarbonate was positively associated and anion gap was inversely associated with MFFM (P < 0.01). Participants in the highest quartile of bicarbonate had fasting insulin 12.76 pmol/l lower [95% confidence interval (CI) 5.96, 19.55; P for trend < 0.01] than those in the lowest quartile. Participants in the highest quartile of anion gap had fasting insulin 4.39 pmol/l higher (95% CI 0.47, 8.31; P for trend < 0.01) than those in the lowest quartile. CONCLUSIONS: Lower bicarbonate and higher anion gap are independently associated with insulin resistance. Further research is needed to elucidate the relations between organic acid production, insulin resistance, and the pathogenesis of Type 2 diabetes.