Dietary supplementation with gamma-linolenic acid or fish oil decreases T lymphocyte proliferation in healthy older humans

Animal and human studies have shown that greatly increasing the amounts of flaxseed oil [rich in the (n-3) polyunsaturated fatty acid (PUFA) alpha -li nolenic acid (ALNA)] or fish oil [FO; rich in the long chain (n-3) PUFA eic osapentaenoic acid (EPA) and docosahexaenoic acid (DHA)] in the diet can de crease mitogen-stimulated lymphocyte proliferation. The objective of this s tudy was to determine the effect of dietary supplementation with moderate l evels of ALNA, gamma -linolenic acid (GLA), arachidonic acid (ARA), DHA or FO on the proliferation of mitogen-stimulated human peripheral blood mononu clear cells (PBMC) and on the production of cytokines by those cells. The s tudy was randomized, placebo-controlled, double-blinded and parallel. Healt hy subjects ages 55-75 y consumed nine capsules/d for 12 wk; the capsules c ontained placebo oil (an 80:20 mix of palm and sunflower seed oils) or blen ds of placebo oil with oils rich in ALNA, GLA, ARA or DHA or FO. Subjects i n these groups consumed 2 g of ALNA or 770 mg of GLA or 680 mg of ARA or 72 0 mg of DHA or 1 g of EPA plus DHA (720 mg of EPA + 280 mg of DHA) daily fr om the capsules. Total fat intake from the capsules was 4 g/d. The fatty ac id composition of PBMC phospholipids was significantly changed in the GLA, ARA, DHA and FO groups. Lymphocyte proliferation was not significantly affe cted by the placebo, ALNA, ARA or DHA treatments. GLA and FO caused a signi ficant decrease (up to 65%) in lymphocyte proliferation. This decrease was partly reversed by 4 wk after stopping the supplementation. None of the tre atments affected the production of interleukin-2 or interferon-gamma by PBM C and none of the treatments affected the number or proportion of T or B ly mphocytes, helper or cytotoxic T lymphocytes or memory helper T lymphocytes in the circulation. We conclude that a moderate level GLA or EPA but not o f other (n-6) or (n-3) PUFA can decrease lymphocyte proliferation but not p roduction of interleukin-2 or interferon-gamma.