Adiposity in Relation to Vitamin D Status and Parathyroid Hormone Levels: A Population-Based Study in Older Men and Women

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Adiposity in Relation to Vitamin D Status and Parathyroid Hormone Levels: A Population-Based Study in Older Men and Women

Abstract

Objective: In small case-control studies, obesity was associated with worse vitamin D status. Our aim was to assess the association of adiposity (anthropometric measures as well as dual energy x-ray absorptiometry) with serum 25-hydroxyvitamin D (25-OH-D) and serum PTH levels in a large population-based study including older men and women.

Results: After adjustment for potential confounders, higher body mass index, waist circumference, and sum of skin folds were statistically significantly associated with lower 25-OH-D (standardized [beta] values were -0.136, -0.137, and -0.140, respectively; all P < 0.05) and with higher PTH (0.166, 0.113, and 0.114, respectively; all P < 0.05). Total body fat percentage was more strongly associated with 25-OH-D and PTH (-0.261 and 0.287, respectively; both P < 0.001) compared with anthropometric measures. Total body fat percentage remained associated with 25-OH-D after adjustment for PTH, and with PTH after adjustment for 25-OH-D.

Results

Recently, evidence has been accumulating that obesity can also be the consequence of a low vitamin D status. Increased PTH levels, of which serum 25-OH-D is an important determinant, promote calcium influx into the adipocytes. In these cells intracellular calcium enhances lipogenesis; therefore, PTH excess may promote weight gain (14, 15). The fact that PTH was also associated with adiposity after adjustment for 25-OH-D could suggest that PTH, also independently of 25-OH-D, contributes to the development of adiposity. The observation that a higher dietary intake of calcium, which is related to lower PTH levels, is related to lower body weight (24) and less weight gain (25) also fits the hypothesis of high PTH levels as a cause of obesity.

These intervention studies suggest a modest, but causal, relation between serum PTH and weight change. Serum 25-OH-D is an important determinant of PTH levels, and interventions have shown that supplementation with [alpha]-calcidol resulted in modest, but significant, weight loss (29, 30). In our study, however, the 25-OH-D level was also related to adiposity independently of PTH levels.

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