title: Seasonal and sex variation of high-sensitivity C-reactive protein in healthy adults: a longitudinal study.
abstract: BACKGROUND
  Cross-sectional studies have reported seasonal variation in high-sensitivity C-reactive protein (hsCRP). However, longitudinal data are lacking.
  
  
  METHODS
  We collected data on diet, physical activity, psychosocial factors, physiology, and anthropometric measurements from 534 healthy adults (mean age 48 years, 48.5% women, 87% white) at quarterly intervals over a 1-year period between 1994 and 1998. Using sinusoidal regression models, we estimated peak-to-trough amplitude and phase of the peaks.
  
  
  RESULTS
  At baseline, average hsCRP was 1.72 mg/L (men, 1.75 mg/L; women, 1.68 mg/L). Overall seasonal variation amplitude was 0.16 mg/L (95% CI 0.02 to 0.30) and was lower in men (0.10 mg/L, 95% CI -0.11 to 0.31) than in women (0.23 mg/L, 95% CI 0.04 to 0.42). In both sexes, hsCRP peaked in November, with a corresponding trough in May. Relative plasma volume, waist and hip circumference, diastolic blood pressure, and depression scores were major factors associated with changes in amplitude of seasonal variation of hsCRP, and taken together explain most of the observed seasonal change. There was a 20% increase in the percentage of participants classified in the high-risk category for hsCRP (> or =3 mg/L) during late fall and early winter compared with late spring and early summer.
  
  
  CONCLUSIONS
  Concentrations of hsCRP were modestly increased in fall and winter compared to summer, with greater seasonal amplitude of variation observed in women. Conventional classification methods fail to consider seasonality in hsCRP and may result in substantial misclassifications in the spring and fall. Future clinical practice and research should take these variations into account.
authors.affiliation: Division of Preventive and Behavioral Medicine and Division of Cardiovascular Medicine, University of Massachusetts Medical School, Worcester, MA 01655, USA.
authors.forename: David E
authors.initials: DE
authors.lastname: Chiriboga
authors.forename: Yunsheng
authors.initials: Y
authors.lastname: Ma
authors.forename: Wenjun
authors.initials: W
authors.lastname: Li
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Stanek
authors.forename: James R
authors.initials: JR
authors.lastname: Hébert
authors.forename: Philip A
authors.initials: PA
authors.lastname: Merriam
authors.forename: Eric S
authors.initials: ES
authors.lastname: Rawson
authors.forename: Ira S
authors.initials: IS
authors.lastname: Ockene
mesh_terms: D000328:Adult; D000368:Aged; D002097:C-Reactive Protein / Q000032:analysis*; D003627:Data Interpretation, Statistical; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D012621:Seasons; D012737:Sex Factors; D055815:Young Adult
chemical_list: D002097:C-Reactive Protein