Kinetics of 13C-DHA before and during fish-oil supplementation in healthy older individuals1-3

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Docosahexaenoic acid (DHA) kinetics appear to change with intake, which is an effect that we studied in an older population by using uniformly carbon-13-labeled DHA (13C-DHA).


We evaluated the influence of a fish-oil supplement over 5 mo on the kinetics of 13C-DHA in older persons.


Thirty-four healthy, cognitively normal participants (12 men, 22 women) aged between 52 and 90 y were recruited. Two identical kinetic studies were performed, each with the use of a single oral dose of 40 mg 13C-DHA. The first kinetic study was performed before participants started taking a 5-mo supplementation that provided 1.4 g DHA/d plus 1.8 g eicosapentaenoic acid (EPA)/d (baseline); the second study was performed during the final month of supplementation (supplement). In both kinetic studies, blood and breath samples were collected ≤8 h and weekly over 4 wk to analyze 13C enrichment.


The time × supplement interaction for 13C-DHA in the plasma was not significant, but there were separate time and supplement effects (P < 0.0001). The area under the curve for plasma 13C-DHA was 60% lower while subjects were taking the supplement than at baseline (P < 0.0001). The uniformly carbon-13-labeled EPA concentration was 2.6 times as high 1 d posttracer while patients were taking the supplement as it was at baseline. The mean (±SEM) plasma 13C-DHA half-life was 4.5 ± 0.4 d at baseline compared with 3.0 ± 0.2 d while taking the supplement (P < 0.0001). Compared with baseline, the mean whole-body half-life was 61% lower while subjects were taking the supplement. The loss of 13C-DHA through β-oxidation to carbon dioxide labeled with carbon-13 increased from 0.085% of dose/h at baseline to 0.208% of dose/h while subjects were taking the supplement.


In older persons, a supplement of 3.2 g EPA + DHA/d increased β-oxidation of 13C-DHA and shortened the plasma 13C-DHA half-life. Therefore, when circulating concentrations of EPA and DHA are increased, more DHA is available for β-oxidation. This trial was registered at as NCT01577004.

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