Dietary docosahexaenoic acid and immunocompetence in young healthy men

The purpose of this study was to examine the effect of dietary docosahexaenoic acid (DHA), in the absence of eicosapentaenoic acid, on human immune response (IR). A 120-d study with 11 healthy men was conducted at the Metabolic Research Unit of the Western Human Nutrition Research Center. Four subjects (control group) were fed the stabilization or basal diet (15, 30, and 55% energy from protein, fat, and carbohydrate, respectively) throughout the study; the remaining seven subjects (DHA group) were fed the basal diet for the first 30 d, followed by 6 g DHA/d for the next 90 d. DHA replaced an equivalent amount of linoleic acid; the two diets were comparable in their total fat and all other nutrients. Both diets were supplemented with 20 mg d-alpha-tocopherol acetate per day. Indices of IR were examined on study day 22, 30, 78, 85, 106, and 113. Addition of DHA at moderately high levels did not alter the proliferation of peripheral blood mononuclear cells cultured with phytohemagglutinin or concanavalin A, or the delayed hypersensitivity skin response. Also, additional DHA did not alter the number of T cells producing interleukin 2 (IL2), the ratio between the helper/suppressor T cells in circulation, or the serum concentrations of immunoglobulin G, C3, and interleukin 2 receptor (IL2R). DHA supplementation, however, caused a significant (P = 0.0001) decrease in the number of circulating white blood cells which was mainly due to a decrease in the number of circulating granulocytes. The number of lymphocytes in peripheral circulation was not affected by Dietary DHA enrichment, but the percentage of lymphocytes in white blood cells increased because of a reduction in granulocyte numbers. None of these indices was changed in the control group. Our results show that when total fat intake is low and held constant, DHA consumption does not inhibit many of the lymphocyte functions which have been reported to be inhibited by fish oil consumption.