Vitamin D status, dependence on age, and seasonal variations in the concentration of vitamin D in Croatian postmenopausal women initially screened for osteoporosis.

Vitamin D deficiency is associated with secondary hyperparathyroidism, increased bone turnover, and bone loss, leading to increased risk for osteoporotic fractures. The objective of this study was to investigate the prevalence of inadequate (insufficient or deficient) serum vitamin D levels in Croatian postmenopausal women initially screened for osteoporosis. Assessment of 25-hydroxyvitamin D (25(OH)D) was performed in 120 Croatian postmenopausal women aged > or =50 years. Three cut-off levels of vitamin D inadequacy were investigated: <75, <50, and <30 nmol/L. Among the included patients, only 14.2% of women complied with diagnostic criteria for osteoporosis. A total of nine (7.5%) had vitamin D levels greater than 75 nmol/L, suggesting that 92.5% of postmenopausal women had inadequate vitamin D status. The prevalence of two different cut-off point groups was 63.3% (<50 nmol/L) and 14.2% (<30 nmol/L). Mean (+/-SD) serum level of 25(OH)D was 46.94 (16.77) nmol/L. Vitamin D was exhibiting declining values with increasing age (r = -0.28; P = 0.002). The prevalence of vitamin D levels below 30 nmol/L was high in patient aged > or =65 years (23.8%). The highest mean level of vitamin D was detected in summer, with significant differences from spring and winter (P = 0.015 and P = 0.022, respectively). The results of this study indicate a high prevalence of vitamin D inadequacy in Croatian postmenopausal women initially screened for osteoporosis. High prevalence coupled with the rising recognition of potential clinical significance of the vitamin D inadequacy makes this highly interesting intervention target, suggesting that the attempts to increase the awareness on this issue are needed.