Plasma incorporation, apparent retroconversion and β-oxidation of 13C-docosahexaenoic acid in the elderly

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 C-13-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 C-13-DHA. Tracer incorporation into fatty acids of plasma triglycerides, free fatty acids, cholesteryl esters and phospholipids, as well as apparent retroconversion and beta-oxidation of C-13-DHA were evaluated 4 h, 24 h, 7d and 28d later. Results: Plasma incorporation and beta-oxidation of C-13-DHA reached a maximum within 4 h in both groups, but C-13-DHA was transiently higher in all plasma lipids of the elderly 4 h to 28d later. At 4 h post-dose, C-13-DHA beta-oxidation was 1.9 times higher in the elderly, but over 7d, cumulative beta-oxidation of C-13-DHA was not different in the two groups (35% in the elderly and 38% in the young). Apparent retroconversion of C-13-DHA was well below 10% of C-13-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 C-13-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.