Prevalence and predictors of vitamin D insufficiency in women of reproductive age living in northern latitude

Objective: This study assessed the prevalence of vitamin D deficiency (serum 25-hydroxyvitamin D (25OHD) <= 50 nmol/l) and insufficiency (serum 25OHD 51-74 nmol/l) during summer and the predictors of serum 25OHD in young women of reproductive age. Design: Cross-sectional study. Methods: Between May and September 2006, 153 healthy, ambulatory and essentially Caucasian women, aged 18-41 years, were recruited. Serum 25OHD and parathyroid hormone (PTH) levels were measured, and questionnaires were evaluated. Results: About 3.9% of women had serum 25OHD <= 50 nmol/l with an additional 26.8% in the insufficient range. Most women (56.9%) had their blood sampled in September. Month of blood collection significantly influenced serum 25OHD. Body mass index (BMI) was inversely associated with serum 25OHD, while traveling to a warmer climate during winter/spring and using oral contraceptive pills (OCP) were associated with higher serum 25OHD. Sunscreen was used by 77.8% of women, but only 3.3% reported consuming vitamin D supplements. BMI, serum PTH, travel to a warmer climate, and OCP use were independently and significantly associated with serum 25OHD, after adjustment for the month of sampling, and explained 40% of the variance in serum 25OHD. Conclusions: In Canada, the prevalence of vitamin D insufficiency is relatively high (30%) during summer in healthy women of reproductive age. Given the expected decrease in serum 25OHD during winter and the low consumption of vitamin D supplements, a high prevalence of vitamin D deficiency and insufficiency is to be anticipated during winter, except maybe for those traveling to a warmer climate.