High Prevalence of Vitamin D Insufficiency in Farming and Nonfarming Populations in South Dakota: Associations With Parathyroid Hormone, Body Fat, and Bone Density.

The purpose of this study was to investigate the role of lifestyle (farming vs nonfarming), age, season, and percent body fat on serum 25-hydroxyvitamin D (25-OHD) and parathyroid hormone (PTH). Serum 25-OHD concentrations were lower in winter than in summer and in older than in younger individuals. Dietary intake of vitamin D was associated with greater serum 25-OHD concentrations. A significant inverse relationship between PTH and 25-OHD was observed in older but not younger individuals. Trabecular volumetric bone mineral density was inversely associated with serum PTH, but not 25-OHD concentrations. Modern farm practices do not necessitate excessive sunlight exposure and that may help explain the lack of differences between farming and nonfarming populations.