title: Serum C3 epimer of 25-hydroxyvitamin D and its determinants in adults: a national health examination survey in Thais.
abstract: A high percentage have detectable C3 epimer of 25-hydroxyvitamin D3 (3-epi-25(OH)D3) in the population of Thai National Health Examination Survey IV.
  
  
  BACKGROUND
  C3 epimers of vitamin D have recently been shown to contribute significantly to 25-hydroxyvitamin D (25(OH)D) levels in an infant population. However, the findings in the general adult population are unclear. Therefore, the purpose of the present study is to determine the percentage of the C3 epimer of 25(OH)D (3-epi-25(OH)D) and its determinants in an adult population.
  
  
  METHODS
  A subsample of 1148 sera randomly selected from the Thai National Health Examination Survey IV (2009) samples were measured for serum 25(OH)D2, 25(OH)D3, 3-epi-25(OH)D2, and 3-epi-25(OH)D3 by LC-MS/MS method. The relative 3-epimer contribution (%) was used to express the amount of 3-epimer-25(OH)D3 as a percentage of total 25(OH)D3 (the sum of 25(OH)D3, and 3-epi-25(OH)D3).
  
  
  RESULTS
  A high proportion of subjects had detectable 3-epi-25(OH)D3 that was <10 % of the total 25(OH)D levels. Since the level of total 25(OH)D2 is low, only a minority of subjects had detectable 3-epi-25(OH)D2. Multivariate analysis suggested that age, male gender, and rural residence were independently related to the 3-epi-25(OH)D3/total 25(OH)D3 ratio.
  
  
  CONCLUSIONS
  A high percentage of Thai adults had detectable 3-epi-25(OH)D3 that was <10 % of the total 25(OH)D levels. Age, gender, and living in a rural area were associated with the relative amount of 3-epi-25(OH)D3 to total 25(OH)D3.
authors: Division of Endocrinology and Metabolism, Department of Medicine, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Rama VI Road, Bangkok, 10400, Thailand, laor.cha@mahidol.ac.th.
authors: L
authors: L
authors: Chailurkit
authors: W
authors: W
authors: Aekplakorn
authors: B
authors: B
authors: Ongphiphadhanakul
mesh_terms: D015652:25-Hydroxyvitamin D 2 / Q000097:blood; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000097:blood; D015992:Body Mass Index; D002112:Calcifediol / Q000097:blood*; D005260:Female; D006306:Health Surveys; D006801:Humans; D008297:Male; D008875:Middle Aged; D011897:Random Allocation; D012016:Reference Values; D012423:Rural Health / Q000706:statistics & numerical data; D012727:Sex Characteristics; D013237:Stereoisomerism; D055815:Young Adult
chemical_list: D015652:25-Hydroxyvitamin D 2; D002112:Calcifediol