October 18, 2006 – Researchers who reviewed all the previous studies on the health impact of eating fish have concluded that avoiding modest fish consumption due to confusion regarding risks and benefits could result in thousands of excess coronary heart disease deaths annually. They found it reduces risk of coronary death by a stunning 36 percent and the rate of death by 17 percent. The report is published in the Journal of the American Medical Association (JAMA).
Fish has been considered a healthy food since the publication of studies demonstrating its various health benefits. Several studies have identified two long-chain omega-3 polyunsaturated fatty acids (n-3 PUFAs), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), as likely playing a role in the associated lower rates of coronary heart disease with fish consumption.
Conversely, concern has arisen over potential harm from mercury, dioxins, and polychlorinated biphenyls (PCBs) present in some fish species. The public is faced with conflicting reports on the risks and benefits of eating fish, resulting in controversy over the role of fish consumption in a healthy diet.
Dariush Mozaffarian, M.D., Dr.P.H., and Eric B. Rimm, Sc.D., of Brigham and Women’s Hospital and Harvard Medical School, Boston, reviewed the scientific evidence for adverse and beneficial health effects of fish consumption (in this report defined as finfish or shellfish).
They searched MEDLINE, governmental reports, and meta-analyses to identify reports published through April 2006 evaluating
(1) intake of fish or fish oil and cardiovascular risk,
(2) effects of methylmercury and fish oil on early neurodevelopment,
(3) risks of methylmercury for cardiovascular and neurologic outcomes in adults, and
(4) health risks of dioxins and PCBs in fish. When possible, meta-analyses were performed to characterize benefits and risks most precisely.
The researchers found that modest consumption of fish (e.g., 1 to 2 servings per week), especially species higher in omega-3 fatty acids (EPA, DHA), reduces risk of coronary death by 36 percent and the rate of death from all causes by 17 percent, and may favorably affect other clinical outcomes.
Intake of 250 mg/d of EPA and DHA appears sufficient for primary prevention. This corresponds to one 6-oz. serving/wk of wild salmon or similar oily fish, or more frequent intake of smaller or less omega-3 PUFA–rich servings.
DHA appears beneficial for, and low-level methylmercury may adversely affect, early neurodevelopment.
Women who are or may become pregnant and nursing mothers should avoid selected species (shark, swordfish, golden bass, and king mackerel; locally caught fish per local advisories) and limit intake of albacore tuna (6 oz./wk) to minimize methylmercury exposure.
“However, emphasis must also be placed on adequate consumption—12 oz./wk—of other fish and shellfish to provide reasonable amounts of DHA and avoid further decreases in already low seafood intake among women (74 percent of women of childbearing age and 85 percent of pregnant women consume less than 6 oz./wk),” the researchers wrote.
Health effects of low-level methylmercury in adults are not clearly established; methylmercury may modestly decrease the cardiovascular benefits of fish intake.
“A variety of seafood should be consumed; individuals with very high consumption (5 servings or more per week) should limit intake of species highest in mercury levels. Levels of dioxins and PCBs in fish are low, and potential carcinogenic and other effects are outweighed by potential benefits of fish intake and should have little impact on choices or consumption of seafood.”
“Avoidance of modest fish consumption due to confusion regarding risks and benefits could result in thousands of excess coronary heart disease deaths annually and suboptimal neurodevelopment in children,” the authors conclude.
Such conflicting views on fish intake have seen the number of omega-3 enriched or fortified products on the market increase as consumers seek omega-3s from ‘safer' sources. Most extracted fish oil are purified to remove contaminants. There are a number of good fish oils on the market, but one of the best new ways to get omega-3 polyunsaturated fats is from krill oil.
This study was supported by a grant from the National Heart, Lung, and Blood Institute, National Institutes of Health.
Mozaffarian D, et al "Fish Intake, Contaminants, and Human Health: Evaluating the Risks and the Benefits" JAMA. 2006; 296:1885-1899.