Obesity and efficacy of vitamin D3 supplementation in healthy black adults.

Abstract

Results from recent clinical trials suggest that vitamin D efficacy against cancermay be influenced by body mass index. As suppression of parathyroid hormone (PTH) is one indicator of vitamin D efficacy, we examined to what extent doses of vitamin D3 supplementation suppress PTH levels in individuals with and without obesity. A total of 328 healthy African Americans were randomized into the following four groups and treated for 3months: placebo, 1,000, 2,000, or 4,000IU/day of vitamin D3 supplementation. Among the participants, 250 individuals with PTH measurements were included in the analysis. Obese individuals (n = 141) experienced a steep reduction of 3-month PTH from placebo to 1,000IU/day of vitamin D3 supplementation, but no further reduction at 2,000 or 4,000IU/day. For non-obese individuals (n = 109), the reduction of 3-month PTH was approximately linear for increasing vitamin D3 doses. At supplementation of 2,000 to 4,000IU/day, 3-month 25(OH)vitamin D levels were high in both non-obese and obese individuals, but the 3-month PTH levels remained about 10pg/mL higher in individuals with obesity. Our findings suggest that excess adiposity confers resistance to vitamin D efficacy in suppressing PTH levels, even when given at high doses.