Two new studies published in the US this week seek to blow out of the water fears that people who regularly consumer seafood are putting themselves at risk due to methylmercury, PCB and dioxin contamination. Rather, the benefits of regular fish consumption on heart disease risk and neurodevelopment were seen to outweigh the risks.
Regular consumption of fish and seafood, particularly varieties high in omega-3 fatty acids DHA and EPA, have been linked most strongly to a reduced risk of heart disease, neurological function in unborn babies – as well as several other benefits including eye health and joint health.
But reports that the presence of contaminants methylmercury, PCBs and dioxins in fish could be harmful to human health have caused confusion – despite the official US Department of Agriculture line that most people should include a variety of fish and seafood in their diets. For pregnant and nursing women, those who may become pregnant, and children under 12, the USDA says that two 12 oz (340g) portions of fish per week (including 6 oz of white canned tuna but excluding certain high-mercury species such as shark, tilefish, swordfish and king mackerel) are safe.
Methylmercury is a form of the naturally occurring heavy metal that is readily absorbed by tissues and has been thought to have a detrimental effect on heart and neurological health. Now-banned PCBs (synthetic organocholorine compounds) that were used in industrial and commercial processes until 1977 but are still present in food sources in small amounts are understood to be carcinogenic.
Faced with conflicting and confusing opinions, some consumers have chosen to avoid fish altogether. Others opt to take purified omega-3 supplements or functional foods (often billed as purified or contaminant-free) instead – a factor that may have contributed to the explosion of products on the market in recent years. (Data from Mintel's Global New Products Database charts 745 new omega-3 products introduced in North America and Europe in 2006 to date - up from 48 new products in the same category in 1998.)
Bill Hogarth, director of the National Oceanic and Atmospheric Administration's (NOAA) marine fisheries service, which co-sponsored the independent study together with FDA, said the results show there should be no change in public health guidelines.
“Seafood is safe and most Americans should incorporate a variety of seafood in their diet to reduce the risk of heart disease,” he told reporters yesterday.
“The contamination scare is largely overblown,” he said, citing that only 9 per cent of the PCBs in the diet come from fish. The rest come from meat and dairy.
“There is a bigger health risk in not eating fish”.
The report was conducted by the US National Academies of Science, Institutes of Medicine, and entitled “Seafood Choices: Balancing Benefits and Risks”.
Hogarth said that the JAMA study from the Harvard School of Public Health was not affiliated with the NOAA/FDA research, but was “very timely and relevant”.
Led by Dariush Mozaffarian, MD, PhD, the Harvard researchers searched MEDLINE, governmental reports, and meta-analyses, as well as hand reviews of references and direct investigator contacts to identify reports published up until April 2006 that covered one of four aspects of fish and fish oil consumption: cardiovascular risk; effects of methylmercury and fish oil on early neurodevelopment; risk of methylmercury for cardiovascular and neurologic outcomes in adults; and health risks of dioxins and polycholorinated biphenyls in fish.
The paper list 207 references for studies taken into consideration.
Dr Mozaffarian said that his study, in addition to reviewing the evidence, also conducted a meta-analysis to quantify the risks and benefits.
On the benefit side, he saw that one to two servings of fish per week – especially those higher in DHA and EPA omega-3, reduced the risk of coronary death by 36 per cent, total mortality by 17 per cent, and may favorably affect other clinical outcomes.
Although maintaining that low levels methylmercury may adversely affect early neurodevelopment, DHA appears beneficial for this. The health effects of low-level mercury in adults are not clearly established, but “but may modestly decrease the cardiovascular benefits of eating fish”.
The researchers also surmised that levels of dioxins and polychlorinated biphenyls are low, and potential cardiovascular and other effects are outweighed by potential benefits of fish intake.
“We were surprised by how little evidence there was of harm,” said Mozaffarian.
The Harvard study also considered the use of fish oil supplements, which may contain between 20 and 80 per cent EPA and DHA by weight, little to no mercury, and variable levels of PCBs and dioxins.
“Functional foods supplemented with EPA and DHA (eg, dairy products, salad dressings, cereals) can also provide reasonable intake to individuals not consuming seafood,” wrote Dr Mozaffarian. But he added: “Compared with supplements, fish intake also provides potentially beneficial protein, vitamin D, and selenium.”
The studies may not have an impact on these markets, however. Since consumer awareness of omega-3 containing products has skyrocketed they may not abandon them so readily. Such products may be more convenient than cooking a fish meal, and increasingly cater for those who do not like the taste of fish. Beyond fears over mercury and PCBs, some consumers prefer to avoid fish because of environmental implications of over-fishing.
Both scientists said that this matter were outside the scope of their studies.
“Environmental issues of aquaculture and fishing are real and important,” said Dr Mozaffarian. “We should try to improve what we do to obtain fish, but I don't think this should confuse the issue. It is an important but unrelated concern.”
Dr Hogarth said that it would be doing consumers “a disservice” if health and environmental issues were tied on together.
For more information go to:
Journal of the American Medical Association (October 18, 2006 Vol 296, No 15)
EUFIC related material:Food contaminants