Comprehensive review backs health benefits of eating fish

Oct 18 2006

There is ample research advocating the nutritional benefits of eating fish and shellfish because fish is high in protein and omega-3 fatty acids.

However in recent years many have voiced concern about the chemicals found in fish, including mercury, PCBs and dioxins, which are usually the result of environmental pollution.

As a result there is confusion amongst the public as to whether the benefits of eating fish are worth the implied risks.

But now as a result of research by scientists at the Harvard School of Public Health (HSPH), some of those concerns have been addressed by the single and most comprehensive analysis to date of fish and health.

In the first review ever, which combines the evidence for major health effects of omega-3 fatty acids, the major health risks of mercury, and the major health risks of PCBs and dioxins in both adults and infants and young children, the researchers say that eating a modest amount of fish per week is beneficial for the health.

This equates to about 3 ounces of farmed salmon or 6 ounces of mackerel, which reduces the risk of death from coronary heart disease (CHD) by 36%.

The research team also say that the combined the results of randomized clinical trials, demonstrates that having fish or fish oil reduces deaths from any causes by 17%.

The comprehensive summary examines levels of omega-3 fatty acids, mercury, PCBs and dioxins in various species of fish and other foods, including chicken, beef, pork, butter and eggs.

Dariush Mozaffarian, lead author of the study and an instructor in epidemiology at HSPH and medicine at Brigham and Women's Hospital, says somehow the evidence on the benefits of eating fish has been lost on the public.

The researchers, Mozaffarian and Eric Rimm, associate professor of epidemiology and nutrition at HSPH, did a comprehensive trawl through publications through to April 2006, in order to evaluate the evidence on the relationship between fish intake and major health benefits, as well as the health risks of mercury, dioxins and PCBs.

For the benefits, the researchers focused on evidence from large prospective studies and randomized clinical trials on cardiovascular health in adults and brain development in infants.

The overall evidence showed that fish consumption lowers the risk of death from heart disease by 36%, and that benefit was related to the level of intake of omega-3 fatty acids, found in higher levels in oily fish such as salmon, bluefish, mackerel, sardines, and herring.

For infants and young children, the researchers say that omega-3 fatty acids from seafood is likely to improve early brain development, and children could obtain that benefit from pregnant or nursing mothers who consume fish.

The researchers found no definite evidence that low-level mercury exposure from seafood consumption had harmful effects on health in adults, but it could lessen the cardiovascular benefit from eating fish.

The researchers agree with the Environmental Protection Agency and the Food and Drug Administration guidelines that women of childbearing age, nursing mothers and young children should eat up to two servings per week of a variety of fish but should avoid larger, predatory fish that have higher levels of mercury such as golden bass, king mackerel, shark and swordfish.

Although some studies have shown that PCBs and dioxins may be carcinogenic, the authors found that the benefits of eating fish far outweighed the potential cancer risks from these chemicals.

The researchers also point out that only 9% of the PCBs and dioxins in the U.S. food supply come from fish and other seafood and more than 90% comes from other foods such as meats, vegetables, and dairy products.

Rimm says the media and others may have contributed to the public confusion over the risks of eating seafood, by greatly exaggerating the unsubstantiated claim of a health risk from fish.

The research appears in the October 18, 2006, issue of The Journal of the American Medical Association.