Vitamin D, parathyroid hormone levels, and the prevalence of metabolic syndrome in community-dwelling older adults

OBJECTIVE - Accumulating research suggests low-circulating vitamin D concentrations, i.e., 25-hydroxyvitamin-D [25(OH)D], may be associated with an increased prevalence of metabolic syndrome; however, previous studies have not accounted for parathyroid hormone (PTH) levels. We examined the association of 25(OH)D and PTH with the prevalence of metabolic syndrome in a community-based cohort of older adults. RESEARCH DESIGN AND METHODS - Participants included 410 men and 660 women, 44-96 years old, who completed a follow-up clinic visit in 1997-1999 as part of the Rancho Bernardo Study. Sex-specific logistic regression models were fit to estimate the odds of ATP III (Adult Treatment Panel III)-defined metabolic syndrome across quintiles of 25(OH)D and PTH, adjusting for age, season, and major lifestyle factors. RESULTS - in men, there was a significant trend (P = 0.03) of increasing adjusted odds for metabolic syndrome with increasing PTH concentrations, primarily due to an odds ratio of 2.02 (95% CI 0.96-4.24) in men In the top quintile ( >= 63 ng/l) of PTH concentration. This association remained unchanged after taking into account 25(OH)D levels and excluding men with diabetes or impaired renal function; it was attenuated after adjustment for the homeostasis model assessment of insulin resistance. Neither PTH in women nor 25(OH)D levels in either sex was related to the metabolic syndrome. CONCLUSIONS - These findings suggest an increased risk of metabolic syndrome with elevated PTH levels in older men and no effect of 25(OH)D concentrations in either sex. The reason for the sex difference in the PTH-metabolic syndrome association is unknown. Prospective studies are necessary to better determine the roles of 25(OH)D and PTH in the etiology of metabolic syndrome.