Risk and Benefit of Decreasing Seafood Consumption in Japan—Docosahexaenoic Acid, Methylmercury and Infant IQ

National statistics show that seafood consumption in Japan is decreasing since the mid-1990s. The risks and benefits of this decreasing seafood consumption was assessed in this study. Intake of docosahexaenoic acid (DHA) and methylmercury (MeHg) of women of childbearing age were estimated by using seafood consumption data of women of age 20–39 in the period 2011–2019 and seafood DHA and MeHg content data to find significantly (p < 0.05) decreasing intake of DHA (2.8 mg/day per year) and MeHg (0.19 μg Hg/day per year) in this period. The effect of the decreasing maternal DHA and MeHg intake on infant IQ was estimated by using the equation developed by the FAO/WHO. Net IQ change (the difference in IQ gain by DHA and IQ loss by MeHg) was constant or even increasing, depending on the assumption, in this period while seafood consumption was significantly decreasing. This was due to the decreasing adverse effect of MeHg, along with saturated DHA-derived benefits on infant IQ, even at the decreased seafood consumption of Japanese women of childbearing age. It was indicated that the recent decreasing trend in seafood consumption in Japan did not have an unfavorable effect on infant IQ.