Distribution of serum 25-hydroxyvitamin D levels of reproductive age Japanese women.

Objectives　The distribution of serum 25-hydroxyvitamin D [25(OH)D] levels among reproductive age Japanese perinatal (prepartum, intrapartum, postpartum) and non-perinatal women remains unknown. In addition to this, vitamin D deficiency cut-off values, which consider the effects of these levels during the perinatal period and infant development, have not been determined. Thus, we systematically reviewed the distribution of serum 25(OH)D levels among reproductive age Japanese women, in order to provide basic data to determine vitamin D deficiency cut-off values.Methods　A systematic literature review was conducted on research published between 1963 and 2015, using PubMed web and Japan Medical Abstracts Society web. The key words "Japan," "Vitamin D," "women," and "pregnant women," were used. After filtering for age, sex, race, indication of numerical number, and duplications, 18 papers were extracted and categorized into reproductive age non-perinatal women (13 papers/22 groups), and reproductive age perinatal women (6 papers/8 groups). The mean serum 25(OH)D levels were grouped by age, test period, and measuring methods.Results　Mean serum 25(OH)D levels among reproductive age non-perinatal women were lower than 20 ng/ml in 10 out of 22 groups (45.4%), and lower than 30 ng/ml in 21 groups (95.5%). The mean serum 25(OH)D level among reproductive age perinatal women was lower than those among reproductive age non-perinatal women. Among reproductive age perinatal women, except for one group that included women in the first trimester of pregnancy (5-10 weeks), the mean serum 25(OH)D levels of the other groups were lower than 20 ng/ml.Conclusion　Serum 25(OH)D levels among reproductive age Japanese women, especially perinatal women, appear to be low. Studies of serum 25(OH)D levels among reproductive age Japanese women are limited; hence, further investigation is required.