Dietary supplementation with eicosapentaenoic acid, but not with other long-chain n-3 or n-6 polyunsaturated fatty acids, decreases natural killer cell activity in healthy subjects aged > 55 y

Background: Animal studies showed that dietary flaxseed oil [rich in the n- 3 polyunsaturated fatty acid alpha -linolenic acid (ALA)], evening primrose oil [rich in the n-6 polyunsaturated fatty acid gamma -linolenic acid (GLA )], and fish oil [rich in the long-chain n-3 polyunsaturated fatty acids ei cosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)] can decrease natu ral killer (NK) cell activity. There have been no studies of the effect on NK cell activity of adding these oils to the diet of humans. Objective: Our objective was to determine the effect of dietary supplementa tion with oil blends rich in ALA, GLA, arachidonic acid (AA), DHA, or EPA p lus DHA (fish oil) on the NK cell activity of human peripheral blood mononu clear cells. Design: A randomized, placebo-controlled, double-blind, parallel study was conducted. Healthy subjects aged 55-75 y consumed 9 capsules/d for 12 wk; t he capsules contained placebo oil (an 80:20 mix of palm and sunflower seed oils) or blends of placebo oil and oils rich in ALA, GLA, AA, DHA, or EPA p lus DHA. Subjects in these groups consumed 2 g ALA, 770 mg GLA, 680 mg AA, 720 mg DHA, or 1 g EPA plus DHA (720 mg EPA + 280 mg DHA) daily, respective ly. Total fat intake from the capsules was 4 g/d. Results: The fatty acid composition of plasma phospholipids changed signifi cantly in the GLA, AA, DHA, and fish oil groups. NK cell activity was not s ignificantly affected by the placebo, ALA, GLA, AA, or DHA treatment. Fish oil caused a significant reduction (mean decline: 48%) in NK cell activity that was fully reversed by 4 wk after supplementation had ceased. Conclusion: A moderate amount of EPA but not of other n-6 or n-3 polyunsatu rated fatty acids can decrease NK cell activity in healthy subjects.