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Founded in 1970 by the "Father of Aerobics"
Kenneth H. Cooper MD, MPH

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Dietary Fish Intake and Risk of Mercury/PCB Exposure

Posted in
Eat better

Monday, Oct 02, 2017

One of the recommendations in the 2015-2020 Dietary Guidelines for Americans is to consume more fatty fish. Groups such as the American Heart Association  encourage us to eat at least 2 servings per week of fatty fish (e.g. salmon) intake to improve heart health. A serving is defined as 3.5 ounces of cooked fish. It is well-established that the omega-3 fatty acids found in such fish help to decrease blood triglyceride levels, as well as resting heart rate and blood pressure. Furthermore, rates of fatal coronary heart disease and stroke are lower in people who eat fish regularly. For example, a large study conducted in Finland showed that men who consumed 1-3 servings of fatty fish per month were 43% less likely to have a stroke than men who did not consume fish.

A concern that many people have about including fish in their diet is the presence of contaminants such as mercury, dioxins, and polychlorinated biphenyls (PCB’s).  While this is a valid concern, it is incorrect to assume that all fish are high in these contaminants; as levels vary considerably among species. Large, older, predatory fish such as shark, swordfish, king mackerel and golden bass (tilefish) have been shown to contain the highest concentrations of contaminants. Accordingly, the FDA and EPA caution pregnant or breastfeeding women, as well as those who might become pregnant to avoid those four types of fish, and to limit intake of white (albacore) tuna to 6 ounces a week. Similar guidelines are in place for young children. However, it is important to note that it is recommended and safe for such individuals to increase their intake of fish that is lower in mercury in order to gain important health benefits. In fact, up to 12 ounces per week of fish that are lower in mercury can be safely consumed by pregnant/breastfeeding women and young children. Among fish that are lower in mercury content are canned light tuna, salmon, pollock, and catfish.

Currently, U.S. women are not meeting recommendations for fish consumption during pregnancy; this may stem from the false perception that all fish are high in contaminants. In a survey of 1,000 pregnant women, 21% of them ate no fish in the previous month, while 75% ate fewer than 4 ounces a week. Women are now strongly encouraged to increase fish consumption during pregnancy for several reasons. First, rates of depression during pregnancy and post-partum are significantly higher in women who have a low intake of omega-3 fatty acids. Additionally, a low maternal intake of omega-3’s has been shown to have adverse effects on the fetus. Sub-optimal fine motor development, as well as sub-optimal verbal IQ have been shown to be significantly more common in children whose mothers had a low fish intake during pregnancy. According to Stephen Ostroff, M.D., an FDA chief scientist “Emerging science now tells us that limiting or avoiding fish during pregnancy and early childhood can mean missing out on important nutrients that can have a positive impact on growth and development as well as on general health.”  

So, in addition to promoting heart health, there is mounting evidence that omega-3 fats are also good for our brain. It is especially important for pregnant and breastfeeding women to increase their fatty fish intake not only for their own health, but for the health of their baby as well.

References

He, K., Rimm, E.B., Merchant, A. (2002). Fish consumption and risk of stroke in men. JAMA, 288(24), 3130-3136.

FDA Consumer Update: New Advice: Pregnant women and Young Children Should Eat More Fish (/ForConsumers/ConsumerUpdates/ucm397443.htm)

Hibbeln, J.R., Davis, J.M., Steer, C. (2007). Maternal seafood consumption in pregnancy and neurodevelopmental outcomes in childhood: an observational cohort study.  Lancet, 369(9561), 578-585.

 

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