Does aging increase vitamin D serum level in healthy postmenopausal women?

Vitamin D deficiency is the most under-diagnosed medical condition in postmenopausal women. There are few epidemiologic studies on vitamin D status of postmenopausal women in Iran. This study aimed to investigate the 25-hydroxyvitamin D levels in postmenopausal women living in Tehran, capital of Iran. In this cross sectional study, 110 women were selected via convenience sampling method from menopause clinic of Tehran Women General Hospital between 2011 and 2012. For each woman, a questionnaire was completed, and 25-hydroxyvitamin D levels were determined by chemiluminescence's immunoassay. Vitamin D deficiency has been considered as a 25(OH)D of less than 20ng/ml. Vitamin D insufficiency has been defined as a 25(OH)D of 21-29ng/ml, and sufficiency as a 25(OH)D of 30-100ng/ml. The data was analyzed by using Pearson correlation test in SPSS version 16. The mean age of women was 52.67±5 years. The mean age at natural menopause onset was 47.66±4.44 years, and the median menopause age was 49.00. The median 25(OH)D level was 19.28 (Inter Quartile Range=26.08). We found vitamin D deficiency and vitamin D insufficiency 52.7% and17.3% respectively. Serum 25(OH) D concentrations were significantly correlated with age(r=0.21, P=0.024). These findings indicate that 25(OH)D level in postmenopausal women from Tehran is low. There is a statistically significant positive correlation between vitamin D concentration and age in late postmenopausal period.