Prevalence and significance of low 25-hydroxyvitamin D concentrations in healthy subjects in Delhi.

BACKGROUND Despite abundant sunlight, rickets and osteomalacia are prevalent in South Asian countries. The cause of this paradox is not clear. OBJECTIVE The objective was to assess 25-hydroxyvitamin D [25(OH)D] status and its functional significance in apparently healthy subjects residing in Delhi, a city in the northern part of India. DESIGN Serum 25(OH)D, total calcium, inorganic phosphate, alkaline phosphatase, intact parathyroid hormone, and 1, 25-dihydroxyvitamin D [1,25(OH)(2)D] were measured in groups of healthy subjects who differed with respect to variables relevant to vitamin D and bone mineral metabolic status, such as direct sunlight exposure, season of measurement, skin pigmentation, dietary calcium and phytate contents, and altered physiologic states such as pregnancy and neonatal age. RESULTS All groups except one with maximum direct sunlight exposure had subnormal concentrations of 25(OH)D. The 25(OH)D-deficient groups tended to have an imbalance in bone mineral metabolic homeostasis when exposed to winter weather and low dietary calcium and high dietary phytate, with significantly low calcium and elevated intact parathyroid hormone concentrations, chemical osteomalacia, or both. Increased values of 1,25(OH)(2)D during pregnancy did not help correct the imbalance in bone mineral metabolic homeostasis. CONCLUSION Healthy subjects with low 25(OH)D concentrations are at risk of bone mineral metabolic imbalance when exposed to factors that strain bone mineral homeostasis.