title: Seasonal vitamin D changes and the impact on health risk assessment.
abstract: OBJECTIVE
  To investigate seasonal variation of vitamin D levels in 148,821 serum samples during a 2year time period in a northern-latitude city in the United States.
  
  
  METHODS
  Total vitamin D assay testing by chemiluminescence was performed on the DiaSorin Liaison. Vitamin D results were extracted from the laboratory information system without patient identification during 2011 and 2012 and separated by season and vitamin D results: less than 10ng/mL (deficient), 10-20.0ng/mL (insufficient), 20.1-30ng/mL (borderline), 30.1-40ng/mL (sufficient), 40.1-100ng/mL, and greater than 100ng/mL.
  
  
  RESULTS
  The seasonal winter period constituted the months of January through March; spring, April through June; summer, July through September; and fall, October through December. The data set analyzed included 36,643 samples during the winter, 38,299 in spring, 36,141 in summer, and 37,738 in fall and demonstrated an expected rise and fall in vitamin D levels.
  
  
  CONCLUSIONS
  This retrospective epidemiological study demonstrates seasonal variation of vitamin D levels at clinical decision points. Although not unexpected, this variation has an impact on studies relating low vitamin D levels to higher rates of cancer, cardiovascular disease, multiple sclerosis, diabetes, autoimmune disease, and a host of other health risk assessments.
authors: NorthShore University HealthSystem, Evanston Hospital, Department of Pathology and Laboratory Medicine, 2650 Ridge Avenue, Evanston, IL 60201, USA. Electronic address: rrosecrans@northshore.org.
authors: Robert
authors: R
authors: Rosecrans
authors: NorthShore University HealthSystem, Evanston Hospital, Department of Pathology and Laboratory Medicine, 2650 Ridge Avenue, Evanston, IL 60201, USA. Electronic address: jdohnal@northshore.org.
authors: James C
authors: JC
authors: Dohnal
mesh_terms: D003684:Dehydrocholesterols / Q000097:blood; D004872:Ergocalciferols / Q000097:blood; D006801:Humans; D049449:Luminescence; D018570:Risk Assessment; D012621:Seasons; D014481:United States; D014807:Vitamin D / Q000097:blood*; D014808:Vitamin D Deficiency / Q000097:blood
chemical_list: D003684:Dehydrocholesterols; D004872:Ergocalciferols; D014807:Vitamin D; C016705:7-dehydrocholesterol
keywords: 7-Dehydrocholesterol; Chemiluminescence; Cholecalciferol; Ergocalciferol