title: Analysis of 25-Hydroxyvitamin D Status According to Age, Gender, and Seasonal Variation.
abstract: BACKGROUND
  The effects of age, gender, and seasonal variation on human levels of 25-hydroxyvitamin D (25(OH)D) are not well understood. In this study, we aimed to investigate 25(OH)D status according to these factors in a Korean population.
  
  
  METHODS
  A total of 303,943 serum 25(OH)D levels were measured using an electrochemiluminescence immunoassay between October 2011 and May 2014. Potential participants were ineligible for the study if they had significant renal, hepatic, or thyroid dysfunction, as well as any major ongoing disease that could influence serum 25(OH)D levels.
  
  
  RESULTS
  A total of 95,137 subjects (49,662 men and 45,475 women) were included in this study. The mean 25(OH)D levels were higher in men (42.4 nmol/l) than in women (32.9 nmol/l, P < 0.001). Among the men and women, 73.0% and 88.9%, respectively, had 25(OH)D levels <50 nmol/l, whereas only 3.8% of men and 1.4% of women had levels >75 nmol/l. The highest mean 25(OH)D value was noted in individuals aged ≥70 for both genders. The proportion of those with 25(OH)D levels <50 nmol/l appeared to be higher among younger subjects (P < 0.001). Lastly, there were significant differences between 25(OH)D levels in individuals during summer to fall and winter to spring in both genders, indicating seasonal periodicity (P < 0.001).
  
  
  CONCLUSIONS
  Serum 25(OH)D status varied according to gender, age, and season. Therefore, analyses of vitamin D status require individualized gender, age, and seasonally adjusted thresholds. Clinicians should consider these factors when determining optimal serum 25(OH)D levels in clinical practice.
authors.affiliation: Department of Laboratory Medicine, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, Korea.
authors.forename: Hui-Jin
authors.initials: HJ
authors.lastname: Yu
authors.affiliation: Department of Laboratory Medicine, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, Korea. mjkkmd@gmail.com.
authors.forename: Min-Jung
authors.initials: MJ
authors.lastname: Kwon
authors.affiliation: Department of Laboratory Medicine, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, Korea.
authors.forename: Hee-Yeon
authors.initials: HY
authors.lastname: Woo
authors.affiliation: Department of Laboratory Medicine, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, Korea.
authors.forename: Hyosoon
authors.initials: H
authors.lastname: Park
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000097:blood*; D000704:Analysis of Variance; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D056910:Republic of Korea; D012189:Retrospective Studies; D012621:Seasons; D012727:Sex Characteristics; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood; D055815:Young Adult
chemical_list: D014807:Vitamin D; C104450:25-hydroxyvitamin D
keywords: 25-hydroxy vitamin D; age; gender; seasonal variation