High prevalence of hypovitaminosis D among pregnant women in southeast China

Vitamin D is essential to maintain bone health, playing a key role in calcium absorption and bone mineralization (1). In addition, it may confer protection against type 1 diabetes mellitus, hypertension, multiple sclerosis and cancer (2). As stores of vitamin D in newborns are reliant on maternal vitamin D status, vitamin D deficiency during pregnancy leads to infant vitamin D deficiency and thus to increased risk of diseases, especially rickets (3). Moreover, because vitamin D can regulate placental development and function, maternal vitamin D deficiency is associated with adverse outcomes of pregnancy, such as miscarriage, preterm birth and preeclampsia (4). Given the importance of vitamin D, the aim of this study is to investigate vitamin D levels of pregnant women in southeast China. One hundred and fifty-two pregnant women of Han race who visited the First Affiliated Hospital of Nanjing Medical University for routine medical checkup for pregnancy agreed to participate in this study. The study population aged 19–41 years (mean ± SD, 27.4 ± 4.15). Samples were collected at 24–28 weeks of gestation. Half of the samples were collected in winter, and the other half were collected in summer. All the participants were urban residents at Nanjing (latitude 31 N, longitude 118 E) in southeast China. Patients with chronic renal failure, liver diseases or therapy with vitamin D were strictly excluded from this study. The hospital’s ethics committee approved this study. And informed written consent was obtained from each subject. Daily intake of dietary vitamin D was calculated from a food-frequency questionnaire. Daily sun exposure was assessed by taking a detailed history of the daily routine including the time of outdoor activities and the type of clothing worn. Sunshine exposure was calculated as hours of exposure ⁄ day · percentage of body surface area exposed. Blood was collected in the fasting condition, and sera were immediately isolated by centrifugation and stored at )70 C for future analysis. Serum 25-hydroxyvitamin D [25(OH)D] level was measured by using a commercial enzyme linked immunosorbent assay (ELISA) kit (IDS, Boldon, UK). The ELISA was performed according to the manufacturer’s protocol and all samples were assayed in triplicate. The ELISA could detect 25(OH)D in the range of 2–152 ng ⁄ mL. And the inter-assay and intra-assay coefficient of variation was 10% and 8%, respectively. For our analysis, we classified the vitamin D status into three groups: vitamin D deficiency [25(OH)D < 10 ng ⁄ mL], vitamin D insufficiency [25(OH)D 10–20 ng ⁄ mL] and vitamin D sufficiency [25(OH)D > 20 ng ⁄ mL]. Difference between the two groups was analysed by unpaired t-test. The significance level was set to <0.05. Data were analysed using SPSS, version 13.0 (SPSS Inc, Chicago, IL, USA). No difference between summer and winter groups was observed in age, body mass index and daily vitamin D intake. However, sun exposure was significant lower in winter group than in summer group (p < 0.01) (Table 1). Mean 25(OH)D concentrations of 152 pregnant women were 10.9 ± 4.78 ng ⁄ mL. The seasonal distribution of serum 25(OH)D levels were shown in Figure 1. Mean serum 25(OH)D level in winter (9.07 ± 5.07 ng ⁄ mL) was Acta Pædiatrica ISSN 0803–5253