Type of fish consumed and thyroid autoimmunity in pregnancy and postpartum

Fish consumption or supplementation with omega-3 fatty acids was reported to cure and/or prevent autoimmune and nonautoimmune disorders. Serum positivity for thyroid autoantibodies is a predictive marker of postpartum thyroiditis and postpartum depression. We hypothesized that stable consumption of the omega-3-rich oily fish was associated with a more favorable profile of serum thyroid antibodies throughout pregnancy and early postpartum compared with stable consumption of swordfish, a predator that concentrates pollutants. We prospectively measured serum thyroglobulin antibodies and thyroperoxidase antibodies in pregnancy (first, second trimesters) and postpartum (day 4), in 236 thyroid disease-free, nonsmoker Caucasian women with stable dietary habits. We did not measure thyroid autoantibodies prior to pregnancy. Women were divided into groups A (n = 48; swordfish), B (n = 52; oily fish), C (n = 68; swordfish + other fish, not necessarily oily fish), and D (n = 68; fish other than swordfish and oily fish). Major endpoints were positivity rates and serum concentrations of the two autoantibodies. We resorted to previous studies for the estimated content of fatty acids and microelements in the consumed fish. Positivity rates and serum concentrations of both antibodies were the greatest in group A and the lowest in group B (P < 0.001 and P < 0.05 to < 0.001, respectively). Relationship between monthly fish consumption and serum concentrations of either antibody was direct in group A but inverse in group B. The estimated content of omega-3 fatty acids in fish consumed by group B was the greatest (P < 0.001 vs. any other group). These data reinforce recommendations that pregnant women should avoid consuming swordfish and indicate consumption of oily fish as a favorable alternative. Because thyroid autoantibodies are markers of autoimmune-related postpartum problems, our data suggest a dietary prophylaxis of such problems.