Vitamin D status and its association with parathyroid hormone concentrations in women of child-bearing age living in Jakarta and Kuala Lumpur

Objective: To describe the vitamin D status of women living in two Asian cities, - Jakarta (6 degrees S) and Kuala-Lumpur (2 degrees N), to examine the association between plasma 25-hydroxyvitamin D and parathyroid hormone (PTH) concentrations, and to determine a threshold for plasma 25-hydroxyvitamin D above which there is no further suppression of PTH. Also, to determine whether dietary calcium intake influences the relationship between PTH and 25-hydroxyvitamin D. Design: Cross-sectional. Setting: Jakarta, Indonesia and Kuala Lumpur, Malaysia. Participants: A convenience sample of 504 non-pregnant women 18 - 40 years. Main measures: Plasma 25-hydroxyvitamin D and PTH. Results: The mean 25-hydroxyvitamin D concentration was 48 nmol/l. Less than 1% of women had a 25-hydroxyvitamin D concentration indicative of vitamin D deficiency (< 17.5 nmol/l); whereas, over 60% of women had a 25-hydroxyvitamin D concentration indicative of insufficiency (< 50 nmol/l). We estimate that 52 nmol/l was the threshold concentration for plasma 25-hydroxyvitamin D above which no further suppression of PTH occurred. Below and above this concentration the slopes of the regression lines were -0.18 (different from 0; P = 0.003) and -0.01 (P = 0.775), respectively. The relation between vitamin D status and parathyroid hormone concentration did not differ between women with low, medium or high calcium intakes (P = 0.611); however, even in the highest tertile of calcium intake, mean calcium intake was only 657 mg/d. Conclusion: On the basis of maximal suppression of PTH we estimate an optimal 25-hydroxyvitamin D concentration of B 50 nmol/l. Many women had a 25-hydroxyvitamin D below this concentration and may benefit from improved vitamin D status.