title: Threshold Effects of Vitamin D Status on Bone Health in Chinese Adolescents With Low Calcium Intake.
abstract: BACKGROUND
  There is no consensus on the definition of vitamin D deficiency for bone health based on serum 25-hydroxyvitamin D (25OHD) levels.
  
  
  OBJECTIVE
  Our objective was to determine whether thresholds exist for associations between 25OHD levels and bone outcomes and if low 25OHD levels have adverse effects on bone health.
  
  
  METHODS
  This is a cross-sectional study.
  
  
  METHODS
  This study included secondary school students in Beijing, China, aged 12-15 years.
  
  
  METHODS
  We measured serum 25OHD; bone mineral density (BMD) of total body, hip, and lumbar spine (LS); serum PTH; bone alkaline phosphatase (BAP); and tartrate-resistant acid phosphatase 5b (TRAP5b) in 222 healthy adolescents (111 girls, 111 boys).
  
  
  RESULTS
  The prevalence of low 25OHD was 61% (<30 nmol/liter) and 97% (<50 nmol/liter) (mean 25OHD, 30 nmol/liter). Dietary calcium intake was low (294 and 307 mg/d for boys and girls, respectively). In girls, break-points for 25OHD (nmol/liter) were: total body BMD 20 (95% confidence interval [CI], 14-27), hip BMD 25 (17-34), LS BMD 22 (14-30), TRAP5b 37 (22-52), and PTH 31 (23-38). In boys, break-points were: total body BMD 39 (24-55), TRAP5b 33 (20-45), and PTH 35 (27-43); no break-points were identified for hip and LS BMD. No break-points were identified for BAP in either gender. Below these break-points, higher 25OHD is associated with increased total body BMD, reduced PTH, and TRAP5b, whereas above these break-points, no such relationship exists.
  
  
  CONCLUSIONS
  Vitamin D deficiency and insufficiency is common in healthy Chinese adolescents. Attaining serum 25OHD levels of more than 20-37 nmol/liter in girls and 33-39 nmol/liter in boys had positive influences on BMD and bone remodelling markers. However, estimates may be affected by low calcium intake and low serum 25OHD levels, with 97% of adolescents having levels below 50 nmol/liter.
authors.affiliation: Menzies Institute for Medical Research (F.W., L.L.L.), University of Tasmania, Hobart, Tasmania 7000, Australia; National Institute for Nutrition and Health (Q.Z.), Chinese Center for Disease Control and Prevention, Beijing 100050, China; and School of Public Health (F.W.), Anhui Medical University, Hefei 230032, Anhui, China.
authors.forename: Feitong
authors.initials: F
authors.lastname: Wu
authors.affiliation: Menzies Institute for Medical Research (F.W., L.L.L.), University of Tasmania, Hobart, Tasmania 7000, Australia; National Institute for Nutrition and Health (Q.Z.), Chinese Center for Disease Control and Prevention, Beijing 100050, China; and School of Public Health (F.W.), Anhui Medical University, Hefei 230032, Anhui, China.
authors.forename: Laura L
authors.initials: LL
authors.lastname: Laslett
authors.affiliation: Menzies Institute for Medical Research (F.W., L.L.L.), University of Tasmania, Hobart, Tasmania 7000, Australia; National Institute for Nutrition and Health (Q.Z.), Chinese Center for Disease Control and Prevention, Beijing 100050, China; and School of Public Health (F.W.), Anhui Medical University, Hefei 230032, Anhui, China.
authors.forename: Qian
authors.initials: Q
authors.lastname: Zhang
mesh_terms: D000293:Adolescent; D000469:Alkaline Phosphatase / Q000097:blood; D000068476:Beijing / Q000453:epidemiology; D015519:Bone Density; D016723:Bone Remodeling; D001842:Bone and Bones / Q000502:physiology*; D002118:Calcium / Q000172:deficiency*; D002136:Calcium, Dietary; D002648:Child; D003430:Cross-Sectional Studies; D019587:Dietary Supplements; D005260:Female; D006304:Health Status; D006801:Humans; D008297:Male; D009752:Nutritional Status; D010281:Parathyroid Hormone / Q000097:blood; D015995:Prevalence; D011627:Puberty / Q000502:physiology; D012737:Sex Factors; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood
chemical_list: D002136:Calcium, Dietary; D010281:Parathyroid Hormone; D014807:Vitamin D; C104450:25-hydroxyvitamin D; D000469:Alkaline Phosphatase; D002118:Calcium