When a pregnant woman eats a fish-rich diet, the mercury content can reduce the beneficial effects fish oil has on her child's brain development. Babies exposed in the womb to higher methyl mercury levels scored lower on skills tests.
Of five nutrients tested, only the benefits of the fish oil DHA were affected by the mercury. The extent to which methyl mercury interferes with fish oil's brain benefits is uncertain.
Environmental Health News reports:
"The beneficial effects of eating fish during pregnancy on a baby's brain development are relatively well accepted. However, some fish can contain high levels of mercury ... Government agency advisories suggest women of childbearing years eat fish with low mercury levels as well as limit consumption of fish that contain high levels."