Pregnant women need fish for fetus
tread a fine line in fish consumption to avoid excess mercury,
suggests a new study on the risks posed by mercury and the benefits
A raft of studies has indicated that omega-3 has an important role to play in brain development, as well as the prevention of heart disease and certain cancers and promotion of bone health. This has driven rapid expansion in functional foods containing omega-3: according to ProductScan, 150 new products containing omega-3 were launched in the USA and Canada in 2004, and 109 were launched in the first five months of 2005.
But just as consumers are becoming more aware of omega-3 and its benefits, a note of caution has issued from the FDA on organic mercury levels in fish, one of the best natural sources of the fatty acid.
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.
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.
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 researchers, led by Emily Oken, set out to study whether women's fish consumption when pregnant harms or benefits fetal brain development.
The study group consisted of 135 mother and infant pairs who were involved in Project Viva, a prospective pregnancy and child cohort study.
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.
Oaken 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.