Very high rates of vitamin D insufficiency in women of child-bearing age living in Beijing and Hong Kong

We aimed to describe the vitamin D status of young women living in two Chinese cities in the spring - Beijing in the north (latitude 39° north) and Hong Kong (latitude 22° north) in the south. We also examined the relationship between serum 25-hydroxyvitamin D and parathyroid hormone (PTH) concentrations to determine a threshold for serum 25-hydroxyvitamin D above which there is no further suppression of PTH. Finally, we examined whether dietary Ca intake influences this relationship. Non-pregnant women aged 18-40 years (n 441) were recruited between February and June. Fasting blood was collected and dietary intakes were assessed using 5 d food records. Mean serum 25-hydroxyvitamin D concentration was lower in Beijing than Hong Kong women (29 v. 34 nmol/l; P < 0.001). Vitamin D deficiency (≤ 25 nmol/l) was indicated in 40 % of Beijing and 18 % of Hong Kong women, and over 90 % of women in both cities were insufficient (≤ 50 nmol/l). Mean Ca and vitamin D intakes were 478 mg/d and 2.0 μg/d, respectively. The relationship between 25-hydroxyvitamin D concentration and PTH was linear throughout the range with a slope of -0.36 (different from 0; P < 0.001; R 0.26), with no apparent threshold. There was no influence of Ca intake on the relationship between 25-hydroxyvitamin D and PTH concentration. Vitamin D deficiency is common and insufficiency is very common in non-pregnant women in Hong Kong and Beijing during spring. Serum 25-hydroxyvitamin D was inversely associated with PTH with no apparent threshold. Strategies such as vitamin D fortification or supplementation may be required.