Abstract
There is a lack of large-scale studies on vitamin D status and its relationship to parathyroid hormone (PTH) and bone turnover markers in adults living in Shanghai. The objectives were to determine the prevalence of vitamin D insufficiency in Shanghai and to investigate the relationship of 25(OH)D with parathyroid function and bone turnover markers. This cross-sectional study involved 649 men and 1939 women aged 20–89 years who were randomly sampled in Shanghai. Serum concentrations of 25(OH)D, PTH, albumin, and bone turnover markers were measured. During the winter season, the prevalence of vitamin D insufficiency (<30 ng/mL) was 84% in males and 89% in females. The prevalence of vitamin D deficiency (<20 ng/mL) was 30% in males and 46% in females. With increasing serum 25(OH)D concentrations categorized as <10, 10–20, 20–30, and ≥30 ng/mL, the mean PTH and bone turnover markers levels gradually decreasd in both sexes (p<0.001). There was an inverse relationship between the serum 25(OH)D and PTH concentrations in both genders, but no threshold of 25(OH)D at which PTH levels plateaued was observed. There were modest but significantly inverse relationships between the levels of 25(OH)D and bone turnover markers, but no plateau was observed for serum 25(OH)D levels up to 40 ng/mL.
Highlights
Vitamin D is known to be an essential element for bone metabolism and skeletal health
There is a lack of large-scale studies on vitamin D status and its relationship to parathyroid hormone (PTH) and bone turnover markers in adults living in Shanghai
All participants were of Han ethnicity and residents of Shanghai
Summary
Vitamin D is known to be an essential element for bone metabolism and skeletal health. In recent years there has been increasing interest in the influence of vitamin D on extraskeletal health. The major source of vitamin D for most humans is exposure to sunlight. Vitamin D3 is synthesized in human skin via the photoisomerization of 7-dehydrocholesterol (7DHC) to yield previtamin D3 during exposure to UVB radiation [9]. Previtamin D3 undergoes hydroxylation in the liver, resulting in the formation of 25-hydroxyvitamin D3 [25(OH)D3], the primary circulatory form. 25(OH)D3 subsequently undergoes hydroxylation in the kidney to yield the biologically active form of vitamin D, calcitriol [1,25-(OH)2D]. For adults in a bathing suit, exposure to the amount of sunlight that causes a slight pinkness of the skin 24 hours later (1MED) is equivalent to ingesting approximately 20,000 IU of vitamin D [6]. Very few foods naturally contain vitamin D, and foods that are fortified with vitamin D are often inadequate to satisfy either a child’s or an adult’s vitamin D requirement [10]
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