Vitamin D status, dependence on age, and seasonal variations in the concentration opf 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 ≥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% (