title: Plasma homocysteine is not subject to seasonal variation.
abstract: BACKGROUND
  Studies investigating the relationship between plasma total homocysteine (tHcy) and vascular disease usually rely on a single measurement. Little information is available, however, on the seasonal variability of plasma tHcy. The aim of this study was to investigate the seasonal variation in fasting plasma tHcy and related B-vitamin intake and status in a group of people who did not consume fortified foods or take B-vitamin supplements.
  
  
  METHODS
  In this longitudinal study, a group of 22 healthy people were followed for 1 year. A fasting blood sample and dietary information were collected from each individual every 3 months, i.e., at the end of each season.
  
  
  RESULTS
  There was no significant seasonal variation in plasma tHcy or in B-vitamin intake or status with the exception of red cell folate (significantly lower in spring compared with autumn or winter) and serum folate (significantly lower in spring compared with the other seasons). Although the between-person variation in plasma tHcy was high (47%), the within-person variation was low (11%). This low variation, combined with the low methodologic imprecision of 3.8%, yielded a high reliability coefficient for plasma tHcy (0.97).
  
  
  CONCLUSIONS
  Although there was a small seasonal variation in folate status, there was no corresponding seasonal variation in plasma tHcy. The high reliability coefficient for plasma tHcy suggests that a single measurement is reflective of an individual's average plasma tHcy concentration, thus indicating its usefulness as a potential predictor of disease. This, however, needs to be confirmed in different subgroups of the population.
authors.affiliation: Northern Ireland Centre for Diet and Health, University of Ulster, Coleraine BT52 1SA, Northern Ireland.
authors.forename: M C
authors.initials: MC
authors.lastname: McKinley
authors.forename: J J
authors.initials: JJ
authors.lastname: Strain
authors.forename: J
authors.initials: J
authors.lastname: McPartlin
authors.forename: J M
authors.initials: JM
authors.lastname: Scott
authors.forename: H
authors.initials: H
authors.lastname: McNulty
mesh_terms: D000293:Adolescent; D000328:Adult; D004032:Diet; D004912:Erythrocytes / Q000737:chemistry; D005215:Fasting; D005260:Female; D005492:Folic Acid / Q000097:blood; D006710:Homocysteine / Q000097:blood*; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D012621:Seasons; D014803:Vitamin B Complex / Q000008:administration & dosage / Q000097:blood
chemical_list: D006710:Homocysteine; D014803:Vitamin B Complex; D005492:Folic Acid