title: Seasonal variation in serum cholesterol levels: treatment implications and possible mechanisms.
abstract: BACKGROUND
  A variety of studies have noted seasonal variation in blood lipid levels. Although the mechanism for this phenomenon is not clear, such variation could result in larger numbers of people being diagnosed as having hypercholesterolemia during the winter.
  
  
  METHODS
  We conducted a longitudinal study of seasonal variation in lipid levels in 517 healthy volunteers from a health maintenance organization serving central Massachusetts. Data collected during a 12-month period for each individual included baseline demographics and quarterly anthropometric, blood lipid, dietary, physical activity, light exposure, and behavioral information. Data were analyzed using sinusoidal regression modeling techniques.
  
  
  RESULTS
  The average total cholesterol level was 222 mg/dL (5.75 mmol/L) in men and 213 mg/dL (5.52 mmol/L) in women. Amplitude of seasonal variation was 3.9 mg/dL (0.10 mmol/L) in men, with a peak in December, and 5.4 mg/dL (0.14 mmol/L) in women, with a peak in January. Seasonal amplitude was greater in hypercholesterolemic participants. Seasonal changes in plasma volume explained a substantial proportion of the observed variation. Overall, 22% more participants had total cholesterol levels of 240 mg/dL or greater (> or =6.22 mmol/L) in the winter than in the summer.
  
  
  CONCLUSIONS
  This study confirms seasonal variation in blood lipid levels and suggests greater amplitude in seasonal variability in women and hypercholesterolemic individuals, with changes in plasma volume accounting for much of the variation. A relative plasma hypervolemia during the summer seems to be linked to increases in temperature and/or physical activity. These findings have implications for lipid screening guidelines. Further research is needed to better understand the effects of a relative winter hemoconcentration.
authors.affiliation: Division of Cardiovascular Medicine, Department of Medicine, University of Massachusetts Medical School, Worcester, MA 01655, USA. Ira.Ockene@umassmed.edu
authors.forename: Ira S
authors.initials: IS
authors.lastname: Ockene
authors.forename: David E
authors.initials: DE
authors.lastname: Chiriboga
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Stanek
authors.forename: Morton G
authors.initials: MG
authors.lastname: Harmatz
authors.forename: Robert
authors.initials: R
authors.lastname: Nicolosi
authors.forename: Gordon
authors.initials: G
authors.lastname: Saperia
authors.forename: Arnold D
authors.initials: AD
authors.lastname: Well
authors.forename: Patty
authors.initials: P
authors.lastname: Freedson
authors.forename: Philip A
authors.initials: PA
authors.lastname: Merriam
authors.forename: George
authors.initials: G
authors.lastname: Reed
authors.forename: Yunsheng
authors.initials: Y
authors.lastname: Ma
authors.forename: Charles E
authors.initials: CE
authors.lastname: Matthews
authors.forename: James R
authors.initials: JR
authors.lastname: Hebert
mesh_terms: D000328:Adult; D002784:Cholesterol / Q000097:blood*; D008076:Cholesterol, HDL / Q000097:blood; D008078:Cholesterol, LDL / Q000097:blood; D005260:Female; D006438:Hemodilution; D006801:Humans; D006937:Hypercholesterolemia / Q000453:epidemiology*; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D010507:Periodicity; D012621:Seasons; D014280:Triglycerides / Q000097:blood; D014481:United States / Q000453:epidemiology
chemical_list: D008076:Cholesterol, HDL; D008078:Cholesterol, LDL; D014280:Triglycerides; D002784:Cholesterol