title: Optimal vitamin D status and its relationship with bone and mineral metabolism in Hong Kong Chinese.
abstract: Although 25-hydroxyvitamin D (25[OH]D) is commonly used to define vitamin D status, there is no consensus on the cutoff levels for vitamin D deficiency and insufficiency. In this study, we aimed to identify the 25(OH)D threshold that maximally suppressed parathyroid hormone (PTH) in Hong Kong Chinese population.
  
  
  
  The study included 5276 participants (70% female) of the Hong Kong Osteoporosis Study aged 20 or above who had total 25(OH)D measured. Three-phase segmented regression was used to identify the optimal break-point between 25(OH)D and PTH.
  
  
  
  The prevalence of vitamin D deficiency observed was 43.8% and the prevalence of insufficient (<75nmol/L) or deficient (<50nmol/L) vitamin D levels was 90.1% in our study population. Using unadjusted three-phase segmented regression, the estimated first and second break-point of 25(OH)D on PTH suppression were 32nmol/L (95% CI: 29-35) and 89nmol/L (95% CI: 77-101) with an r2of 0.048, whereas the estimated first and second break-point of 25(OH)D were 27nmol/L (95% CI: 24-30) and 47nmol/L (95% CI: 37-56) after adjusting for factors affecting bone and mineral metabolism. In addition, the relationship between 25(OH)D and PTH significantly differed by sex and age.
  
  
  
  The threshold for 25OHD at the point of maximal suppression of PTH estimated in this study was lower than the suggested threshold of vitamin D deficiency in the literature, perhaps due to race or assay differences, and the relationship between vitamin D and PTH changed with sex and age. Standardization in the methodology of searching for the optimal break-point is desirable so that a consensus on cutoff points can be obtained.
authors.affiliation: Department of Pharmacology and Pharmacy, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong; Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong.
authors.forename: Raymond Yh
authors.initials: RY
authors.lastname: Leung
authors.affiliation: Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong; The State Key Laboratory of Pharmaceutical Biotechnology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong.
authors.forename: Bernard My
authors.initials: BM
authors.lastname: Cheung
authors.affiliation: University of Massachusetts Medical School, Worcester, MA, United States; Boston University School of Medicine, Boston, MA, United States.
authors.forename: Uyen-Sa
authors.initials: US
authors.lastname: Nguyen
authors.affiliation: Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong.
authors.forename: Annie Wc
authors.initials: AW
authors.lastname: Kung
authors.affiliation: Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong.
authors.forename: Kathryn Cb
authors.initials: KC
authors.lastname: Tan
authors.affiliation: Department of Pharmacology and Pharmacy, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong; Centre for Genomic Sciences, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong. Electronic address: lung1212@hku.hk.
authors.forename: Ching-Lung
authors.initials: CL
authors.lastname: Cheung
mesh_terms: D000328:Adult; D000368:Aged; D044466:Asian People; D001842:Bone and Bones / Q000378:metabolism*; D005260:Female; D006723:Hong Kong; D006801:Humans; D008297:Male; D008875:Middle Aged; D008903:Minerals / Q000378:metabolism*; D010281:Parathyroid Hormone / Q000097:blood; D014807:Vitamin D / Q000031:analogs & derivatives / Q000097:blood*; D055815:Young Adult
chemical_list: D008903:Minerals; D010281:Parathyroid Hormone; D014807:Vitamin D; C104450:25-hydroxyvitamin D
keywords: Bone health; Parathyroid hormone; Threshold level; Vitamin D