Behavioural and physical characteristics associated with vitamin D status in women

For most people in Australia, the primary source of vitamin D is casual exposure to sunlight. Hypovitaminosis D has been reported for high-risk populations, but little has been documented for women of all ages living in the community. Using cross-sectional data, we aimed to describe physical and behavioural characteristics associated with serum 25-hydroxyvitamin D (25OHD) for such women and to determine the association of serum 25OHD with hypertension and bone health. Serum 25OHD, parathyroid hormone (PTH), blood pressure, bone mineral density (BMD) and anthropometry were measured in a random sample of 861 women aged 20-92 years enrolled in the Geelong Osteoporosis Study, set in a temperate region at latitude 38-39 degrees S. Lifestyle factors (including diet, smoking, medication use, socio-economic status, residence, education, occupation, and physical activity) were documented by questionnaire. In season-adjusted models for women aged 20-54 years, physical activity and living with a partner were independently and positively associated with serum 25OHD; associations with weight and waist-hip ratio were negative. Among older women, physical activity, vitamin D intake and urban dwelling were positively associated with serum 25OHD; age, weight and smoking were negative. Compared with the lowest tertile, those in the highest serum 25OHD tertile were less likely to have elevated serum PTH (adjusted OR=0.25, 95% CI 0.16-0.41) and high blood pressure (adjusted OR=0.40, 95% CI 0.22-0.72), and more likely to have normal hip and spine BMD (adjusted OR=1.65, 95% CI 1.08-2.52). In multivariable models adjusting for season, age, weight (and height), BMD was associated with serum 25OHD at the spine, hip and whole body; no associations were detected at the forearm and no other characteristics were identified as confounders. Factors associated with high vitamin D status generally reflected healthy body habitus and active lifestyles. In contrast, excessive weight and smoking were associated with poorer vitamin D status. Women with high vitamin D were less likely to have elevated PTH, hypertension or bone deficits than women with poor levels.