High prevalence of vitamin D deficiency among middle-aged and elderly individuals in northwestern China: its relationship to osteoporosis and lifestyle factors.

PURPOSE: Vitamin D deficiency has reached epidemic proportions; this deficiency has been associated with osteoporosis and certain lifestyle factors in adults. This relationship is not well documented among the Lanzhou population in northwest China. This study sought to determine the prevalence of vitamin D deficiency and its risk factors in addition to its relationship with osteoporosis in a Chinese population living in Lanzhou. METHODS: This cross-sectional study involved 2942 men and 7158 women aged 40-75years who were randomly selected from 3 communities in the Lanzhou urban district and examined medically. Levels of 25-hydroxy-vitamin D [25(OH)D] and other parameters were measured according to detailed inclusion criteria. Vitamin D deficiency was defined as serum 25(OH)D levels below 20ng/mL. Calcaneus bone mineral density (BMD) was measured by quantitative ultrasound (QUS). RESULTS: The prevalence of vitamin D deficiency (25(OH)D levels <20ng/mL) was present in 75.2% of the entire study population. Vitamin D deficiency was more prevalent in women (79.7%) than in men (64%; P<0.001). Multiple logistic regression analysis revealed that the significant predictors of vitamin D deficiency included coronary heart disease (CHD), obesity, dyslipidemia, older age, female sex, and smoking (all P<0.05), whereas tea intake, moderate physical activity, milk intake, vitamin D supplementation and sun exposure were protective (all P<0.05). No significant difference in calcaneus BMD measured by QUS was noted between subjects with <20ng/mL and ≥20ng/mL vitamin D levels (0.53±0.13 vs. 0.54±0.13; P=0.089). The risk of having osteoporosis did not increase when vitamin D levels decreased from ≥20ng/mL to <20ng/mL after multiple adjustments (OR=1.00; 95% CI 0.85-1.16; P=0.357). CONCLUSIONS: Vitamin D deficiency is prevalent in the middle-aged and elderly northwestern Chinese population and is largely attributed to CHD, obesity, dyslipidemia, older age, female sex, and smoking. Reduced 25(OH)D levels are not associated with an increased osteoporosis risk.