Original Full Length ArticleHigh prevalence of vitamin D deficiency among middle-aged and elderly individuals in northwestern China: Its relationship to osteoporosis and lifestyle factors
Introduction
Osteoporotic fracture has become a major global public health problem, and it is associated with increased mortality, concomitant morbidity, and reduced quality of life [1]. China, with a rapidly developing economy and large aging population, is experiencing a growing osteoporosis pandemic [2]. Many osteoporotic risk factors have been identified. Vitamin D plays a classically important role in calcium regulation and bone metabolism [3], [4]. Well-known consequences of vitamin D deficiency include secondary hyperparathyroidism, accelerated bone loss, increased bone turnover, proximal muscle weakness, increased body sway, falls, osteoporosis, and fractures [5], [6]. Accumulating evidence suggests that vitamin D levels are inversely related to osteoporosis in observational studies in Western populations [7], [8]; however, evidence from the Chinese population is limited [10].
The prevalence of vitamin D deficiency has increased worldwide [11]. Even in countries with plentiful sunlight, vitamin D inadequacy is observed in 64% of postmenopausal women with osteoporosis [12]. Between 40% and 100% of elderly US and European non-hospitalized men and women are classified as either vitamin D deficient or insufficient [13].
China covers a large area, and regions at different latitudes receive different amounts of sunlight. Lanzhou, which is located on the northwestern inland of China, has a temperate continental climate with different seasons (latitude of 35°5″–38°N and longitude of 102°30″–104°30″E) and is the capital of Gansu province, with a population of over 3 million. The average duration of sunshine in Lanzhou is 2446 h per year, and the average temperature is 11.2 °C [14]. Vitamin D deficiency is common in middle-aged and elderly individuals in Beijing and Shanghai [15]. However, less is known regarding the vitamin D status of the northwestern Chinese population. Furthermore, there has been no epidemiological study on the effects of vitamin D deficiency on osteoporosis and its relationship to lifestyle factors among the Lanzhou population. Thus, the main objectives of the present study were (1) to examine vitamin D status and (2) to assess risk factors for vitamin D deficiency and its relationship with osteoporosis in a representative sample of women and men aged 40–75 years in northwest China.
Section snippets
Study participants
The present work was one part of the baseline survey from the REACTION study that investigated the association of diabetes and cancer, which was conducted among 259,657 adults aged 40 years and older in 25 communities across mainland China from 2011 to 2012 [16]. In brief, subjects were randomly selected from 3 communities in the Lanzhou urban district using stratified, multistage probability population sampling. Only persons who had been living in their current residence for at least 6 months
Vitamin D status of the whole study population
The overall mean (± SD) serum 25(OH)D level was 16.38 ± 6.98 ng/mL. The prevalence of vitamin D deficiency was 75.2% in the whole study population. The vitamin D status of all participants according to different characteristics is summarized in Table 1. The studied population aged 70–75 years exhibited a mean serum 25(OH)D level that was significantly lower than the studied population who were aged < 70 years (P < 0.001). Indeed, there was a significant difference in the prevalence of vitamin D
Discussion
It is assumed that populations living in sunny locations, such as Lanzhou, northwestern China, would be less likely to be vitamin D deficient because of abundant sunshine throughout the year. However, the results of the present study challenge this assumption. The present study clearly demonstrated that vitamin D deficiency was common in Lanzhou. Moreover, in this population, we determined that CHD, dyslipidemia, older age, female sex, and smoking were independent predictors of vitamin D
Conclusions
In summary, vitamin D deficiency is very common (75.2% with 25(OH)D < 20 ng/mL) in a middle-aged and elderly Chinese northwestern population, particularly functional deficiency among those who were women, obese, and age 70–75 years with CHD or dyslipidemia, corresponding to 79.7% of women and 64% of men. Other factors include smoking in men. Moreover, reduced 25(OH)D levels were not associated with an increased osteoporosis risk.
Acknowledgments
The authors wish to thank the support from grants from the Clinical Medicine Foundation of Chinese Medical Association for Endocrine Disease (12010050264), the Natural Science Foundation of Gansu, China (1308RJZA254), and the Chinese Society of Endocrinology and National Clinical Research Center for Metabolic Diseases (1994DP131044). We are grateful to all members of the REACTION group in Lanzhou for their assistance in data collection. We especially thank Dr. Xiaomei Yang for technical
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