Pregnant women need fish for fetus

10/5/2005 - Women wanting to boost their babies’ cognitive development need to tread a fine line in fish meat consumption to avoid excess mercury, suggests a new study on the risks posed by mercury and the benefits of omega-3. Alternatives would be to take marine oil supplements that contain low or non-detectible amounts of mercury. Many supplement providers use molecular distillation to remove heavy metals, such as mercury, and pesticides found in the fish meat samples.

Certain fish contain higher levels of mercury, which is believed to affect the development of a baby or young child's nervous system. The FDA therefore recommends that women who may become pregnant, pregnant women, and nursing mothers eat up to 12 ounces (two average meals) of fish that are low in mercury each week, such as shrimp, canned light tuna, salmon, Pollock and catfish. Other suggestions are to take omega-3 supplements to obtain the benefits of omega-3 fatty acids.

Since albacore or white tuna contains more mercury than light tuna, it should be restricted to one 6 ounce serving per week. Shark, swordfish, king mackerel and tilefish, which contain high levels of mercury, should be avoided altogether. As for young children, the advice on fish types is the same, but the portion sizes should be smaller. Again, supplements will offer more omega-3 fatty acids and little if any of the negatives of consuming fish meat.

However there are concerns that women may err on the side of caution and avoid fish altogether during pregnancy – an approach that researchers from the Department of Ambulatory Care and Prevention at Harvard Medical School believe may also be detrimental to fetal brain development. Indeed, in a presentation at IFT in New Orleans in July, George Gray of Harvard Business School said that fish consumption by women fell by 17 percent following the FDA advice, issued in March 2004.

The study team, led by Emily Oken, MD, MPH, measured maternal fish intake during pregnancy and maternal hair mercury levels at delivery among 135 mother-infant pairs in Project Viva, a long-term study of maternal nutrition and child health. They also assessed infant cognition at six months using a visual recognition memory test. The mothers recorded their consumption of canned tuna, shellfish, dark meat fish and other types of fish in a food frequency questionnaire throughout the second trimester. On average, they ate 1.2 servings of fish. Samples of their hair were taken when they gave birth, and analyzed for mercury content. At six months, the infants' cognitive ability was assessed using visual recognition memory (VRM) testing. The average VRM score was 59.8, and the average maternal hair mercury was 0.55ppm. In ten percent of the women, hair mercury ppm was over 1.2. Oken and her team found that higher fish intake was associated with higher infant cognition. After adjustment for hair mercury level, for each additional weekly fish serving the VRM score was 4 points higher. However, in increase of 1ppm of mercury resulted in a 7.5 drop in VRM score. Oken determined infants whose mothers consumed more than two servings of fish per week but had mercury levels of 1.2ppm or lower had the highest VRM scores.

“Women should continue to eat fish during pregnancy but choose varieties with lower mercury contamination,” wrote the researchers in the October issue of Environmental Health Perspectives.

In a white paper issued in July, the Council for Responsible Nutrition advised the general population to increase its intake of oily fish or take supplements to obtain protective intake levels of about 0.5g of omega-3 per day. Although dietary supplements were outside the scope of the Harvard study, they may prove beneficial for people who are concerned about the detrimental effects of mercury levels or who have some other aversion to fish.

A survey conducted earlier this year by Environmental Defense into measures taken by supplement makers to ensure their fish oil products were contaminant-free concluded that the majority adhere to the strictest standards. Companies, Coromega and Yasoo, both use contaminant-free oil that has went though the process known as molecular distillation.

« Back to All News Articles