title: Seasonal variation in cardiovascular disease risk factors in a subarctic population: the Tromsø Study 1979-2008.
abstract: BACKGROUND
  Seasonal changes in cardiovascular disease (CVD) risk factors may be due to exposure to seasonal environmental variables like temperature and acute infections or seasonal behavioural patterns in physical activity and diet. Investigating the seasonal pattern of risk factors should help determine the causes of the seasonal pattern in CVD. Few studies have investigated the seasonal variation in risk factors using repeated measurements from the same individual, which is important as individual and population seasonal patterns may differ.
  
  
  METHODS
  The authors investigated the seasonal pattern in systolic and diastolic blood pressure, heart rate, body weight, total cholesterol, triglycerides, high-density lipoprotein cholesterol, C reactive protein and fibrinogen. Measurements came from 38 037 participants in the population-based cohort, the Tromsø Study, examined up to eight times from 1979 to 2008. Individual and population seasonal patterns were estimated using a cosinor in a mixed model.
  
  
  RESULTS
  All risk factors had a highly statistically significant seasonal pattern with a peak time in winter, except for triglycerides (peak in autumn), C reactive protein and fibrinogen (peak in spring). The sizes of the seasonal variations were clinically modest.
  
  
  CONCLUSIONS
  Although the authors found highly statistically significant individual seasonal patterns for all risk factors, the sizes of the changes were modest, probably because this subarctic population is well adapted to a harsh climate. Better protection against seasonal risk factors like cold weather could help reduce the winter excess in CVD observed in milder climates.
authors.affiliation: Department of Community Medicine, University of Tromsø, Tromsø, Norway. laila.hopstock@uit.no
authors.forename: Laila Arnesdatter
authors.initials: LA
authors.lastname: Hopstock
authors.forename: Adrian Gerard
authors.initials: AG
authors.lastname: Barnett
authors.forename: Kaare Harald
authors.initials: KH
authors.lastname: Bønaa
authors.forename: Jan
authors.initials: J
authors.lastname: Mannsverk
authors.forename: Inger
authors.initials: I
authors.lastname: Njølstad
authors.forename: Tom
authors.initials: T
authors.lastname: Wilsgaard
mesh_terms: D000328:Adult; D000368:Aged; D001794:Blood Pressure / Q000502:physiology; D015992:Body Mass Index; D001835:Body Weight; D002097:C-Reactive Protein / Q000032:analysis; D002318:Cardiovascular Diseases / Q000097:blood / Q000453:epidemiology* / Q000209:etiology; D002784:Cholesterol / Q000097:blood; D003430:Cross-Sectional Studies; D005260:Female; D005340:Fibrinogen / Q000032:analysis; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D009664:Norway / Q000453:epidemiology; D011159:Population Surveillance; D012307:Risk Factors; D012621:Seasons; D013997:Time Factors; D014280:Triglycerides / Q000097:blood
chemical_list: D014280:Triglycerides; D005340:Fibrinogen; D002097:C-Reactive Protein; D002784:Cholesterol