Seasonal variations of vitamin D status in Greek postmenopausal women receiving enriched dairy products for 30 months: the Postmenopausal Health Study.

The effectiveness of a 30-month dietary intervention on vitamin D status of Greek postmenopausal women was examined. Sixty-six postmenopausal women (55-65 years old) were randomized into an intervention group (IG), receiving a daily dose of 7.5 μg of vitamin D₃ for 12 months that increased to 22.5 μg for the remaining 18 months of intervention through fortified dairy products and attending nutrition and lifestyle counselling sessions, and a control group (CG). After 30 months of intervention, during winter, serum 25-hydroxy vitamin D (25(OH)D) levels significantly decreased in the CG while remained in the same high levels as in the summer period in the IG. Similarly, at 30 months of intervention the prevalence of vitamin D insufficiency was significantly higher in the CG compared to the IG (60.0 vs 25.0%, P = 0.006). In conclusion, the current intervention scheme with a daily dose of 22.5 μg of Vitamin D could significantly decrease the prevalence of vitamin D insufficiency during winter time but not entirely prevent it.