Prevalence and seasonal variation of hypovitaminosis D and its relationship to bone metabolism in community dwelling postmenopausal Hungarian women

Hypovitaminosis D can result in low bone mass. The prevalence of hypovitaminosis D has public health implications, especially where data are lacking. Since diet and sunlight are the two souces of vitamin D, the results obtained in one geographical region may not be universally applicable. The aim of this study is to characterize the prevalence and seasonal variation of hypovitaminosis D and its relationship to bone metabolism in community dwelling postmenopausal Hungarian women. We determined serum levels of 25-hydroxyvitamin D (25-OH-D), PTH, osteocalcin (OC), degradation products of C-terminal telopeptides of type-I collagen (CTx), dietary calcium intake and BMD at L2–L4 lumbar spine (LS) and femur neck (FN) in 319 randomly selected ambulatory postmenopausal women. The prevalence of hypovitaminosis D (serum 25-OH-D≤50 nmol/l) was 56.7%. On comparing patients with normal and low 25-OH-D, a significant difference was found in age (61.6±8.5 years versus 67.3±9.9 years; P<0.001), PTH (3.9±1.9 pmol/l versus 4.3±2.7 pmol/l; P<0.05), FN BMD (0.802±0.123 g/cm² versus 0.744±0.125 g/cm²; P<0.001) and dietary calcium intake (714.4±199.4 g/day versus 607.9±233 g/day; P<0.001). Osteoporotic patients had a significantly lower 25-OH-D (37.6±19.8 nmol/l versus 56.4±24 nmol/l; P<0.001) and dietary calcium intake (519.2±244.5 mg/day versus 718.2±164.3 mg/day; P<0.001). After controlling for all other variables, 25-OH-D was found to be significantly associated with age, the average hours of sunshine in the 3 months prior to 25-OH-D level determination and dietary calcium intake (r ²=0.190; P<0.001). For FN BMD, significant independent predictors were age, body mass index, 25-OH-D and dietary calcium intake (r ²=0.435; P<0.001). The prevalence of hypovitaminosis D during spring, summer, autumn and winter was 71%, 46.3%, 49.4% and 56.7%, respectively. There was significant seasonal variation in 25-OH-D, PTH, OC, calcium intake and FN BMD. There is a high prevalence of hypovitaminosis D in healthy postmenopausal Hungarian women, and FN BMD is associated with serum 25-OH-D and dietary calcium intake.