Presence of impaired intestinal calcium absorption in chronic hypovitaminosis D and its change after cholecalciferol supplementation: assessment by the calcium load test

Abstract

Background: Hypovitaminosis D is common in Asian Indians and its functional significance is currently under investigation. Previous studies have reported on the effect of low serum 25(OH)D levels (<50 nmol L^-1) on bone mineral density and serum parathyroid hormone values. The present study assessed the effect of chronic hypovitaminosis D in Asian Indians on intestinal calcium absorption and its change after cholecalciferol supplementation. Methods: Subjects included 29 healthy volunteers [mean (SD) age, 28.4 ± 6.4 years] with low serum 25(OH)D levels on screening. Intestinal calcium absorption was assessed by the 'calcium load test' with 1 g of oral elemental calcium. Subjects were put on a calcium restricted diet 1 week prior to the test. The calcium load test was repeated in 26 of them after 8 weeks of supplementation with oral cholecalciferol (60 000 IU week^-1). Results: The mean urinary calcium/creatinine ratio of the study subjects was 0.027 ± 0.023 mg mg^-1 under fasting conditions and increased to 0.035 ± 0.032 mg mg^-1 after calcium loading (delta change = 29.6%, P = 0.33). After 8 weeks of cholecalciferol supplementation, the mean serum 25(OH)D increased from 18.9 ± 11.9 to 84.4 ± 34.9 nmol L^-1 (P < 0.0001). Concomitantly, the mean urinary calcium/creatinine ratio of the study subjects increased from 0.030 ± 0.024 mg mg^-1 under fasting conditions to 0.059 ± 0.045 mg mg^-1 after calcium loading (delta change = 96.6%, P = 0.008). Conclusions: The results obtained in the present study show that chronic hypovitaminosis D in Asian Indians has functional relevance in terms of its effect on intestinal calcium absorption, which improves with cholecalciferol supplementation. These findings support the need for improving the vitamin D status of Asian Indians through dietary supplementation and exposure to sunshine.