title: Plasma incorporation, apparent retroconversion and β-oxidation of 13C-docosahexaenoic acid in the elderly.
abstract: BACKGROUND
  Higher fish or higher docosahexaenoic acid (DHA) intake normally correlates positively with higher plasma DHA level, but recent evidence suggests that the positive relationship between intake and plasma levels of DHA is less clear in the elderly.
  
  
  METHODS
  We compared the metabolism of 13C-DHA in six healthy elderly (mean - 77 y old) and six young adults (mean - 27 y old). All participants were given a single oral dose of 50 mg of uniformly labelled 13C-DHA. Tracer incorporation into fatty acids of plasma triglycerides, free fatty acids, cholesteryl esters and phospholipids, as well as apparent retroconversion and β-oxidation of 13C-DHA were evaluated 4 h, 24 h, 7d and 28d later.
  
  
  RESULTS
  Plasma incorporation and β-oxidation of 13C-DHA reached a maximum within 4 h in both groups, but 13C-DHA was transiently higher in all plasma lipids of the elderly 4 h to 28d later. At 4 h post-dose, 13C-DHA β-oxidation was 1.9 times higher in the elderly, but over 7d, cumulative β-oxidation of 13C-DHA was not different in the two groups (35% in the elderly and 38% in the young). Apparent retroconversion of 13C-DHA was well below 10% of 13C-DHA recovered in plasma at all time points, and was 2.1 times higher in the elderly 24 h and 7d after tracer intake.
  
  
  CONCLUSIONS
  We conclude that 13C-DHA metabolism changes significantly during healthy aging. Since DHA is a potentially important molecule in neuro-protection, these changes may be relevant to the higher vulnerability of the elderly to cognitive decline.
authors.affiliation: Research Center on Aging, Health and Social Sciences Center -- Sherbrooke University Geriatrics Institute, Department of Medicine, Université de Sherbrooke, Canada. melanie.plourde2@usherbrooke.ca.
authors.forename: Mélanie
authors.initials: M
authors.lastname: Plourde
authors.forename: Raphaël
authors.initials: R
authors.lastname: Chouinard-Watkins
authors.forename: Milène
authors.initials: M
authors.lastname: Vandal
authors.forename: Ying
authors.initials: Y
authors.lastname: Zhang
authors.forename: Peter
authors.initials: P
authors.lastname: Lawrence
authors.forename: J Thomas
authors.initials: JT
authors.lastname: Brenna
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Cunnane