Predicting the effects of supplemental EPA and DHA on the omega-3 index

Background: Supplemental long-chain omega-3 (n-3) fatty acids (EPA and DHA) raise erythrocyte EPA + DHA [omega-3 index (O3I)] concentrations, but the magnitude or variability of this effect is unclear. Objective: The purpose of this study was to model the effects of supplemental EPA + DHA on the O3I. Methods: Deidentified data from 1422 individuals from 14 published n-3 intervention trials were included. Variables considered included dose, baseline O3I, sex, age, weight, height, chemical form [ethyl ester (EE) compared with triglyceride (TG)], and duration of treatment. The O3I was measured by the same method in all included studies. Variables were selected by stepwise regression using the Bayesian information criterion. Results: Individuals supplemented with EPA + DHA (n = 846) took a mean +/- SD of 1983 +/- 1297 mg/d, and the placebo controls (n = 576) took none. The mean duration of supplementation was 13.6 +/- 6.0 wk. The O3I increased from 4.9% +/- 1.7% to 8.1% +/- 2.7% in the supplemented individuals (P < 0.0001). The final model included dose, baseline O3I, and chemical formulation type (EE or TG), and these explained 62% of the variance in response (P < 0.0001). The model predicted that the final O3I (and 95% CI) for a population like this, with a baseline concentration of 4.9%, given 850 mg/d of EPA + DHA EE would be similar to 6.5% (95% CI: 6.3%, 6.7%). Gram for gram, TG-based supplements increased the O3I by about 1 percentage point more than EE products. Conclusions: Of the factors tested, only baseline O3I, dose, and chemical formulation were significant predictors of O3I response to supplementation. The model developed here can be used by researchers to help estimate the O3I response to a given EPA + DHA dose and chemical form.