Fish is good – fish is bad. Balancing health risks and benefits

Harvard Center for Risk Analysis explores this issue

Fish has been a staple of human nutrition in many cultures, but there has been some controversy recently about the benefits and risks of fish consumption. For example, fish supplies polyunsaturated fatty acids (PUFAs), substances that might protect against coronary heart disease (CHD) and stroke. On the other hand, fish supplies methyl mercury (MeHg), a compound implicated in impairment of cognitive development and IQ. How can the consumer decide whether to increase or decrease consumption? What steps should governments, public health authorities and commercial fishing industries take in response to these conflicting facts?

Joshua T. Cohen, PhD, of the Harvard School of Public Health, writes, “Because fish consumption confers both benefits and risks, the advisories issued by the U.S. federal government raise the possibility of a classic risk–risk trade-off: by avoiding one risk (exposure to MeHg), consumers who follow these advisories may be incurring another (adverse health consequences associated with lower n-3 PUFA intake). Likewise, individuals who increase their consumption of fish because of this food’s nutritional benefits may incur risks associated with MeHg exposure.”

In a series of articles published in the current issue of the American Journal of Preventive Medicine, the results of detailed analyses of the available literature sheds some light on this quandary. The Harvard Center for Risk Analysis undertook a project to create a decision model to evaluate policies that influence population fish consumption. Although much of this work was supported by grants from the National Food Processors Association Research Fund and the Fisheries Scholarship Fund, neither organization controlled the research findings or interpretations of the results.

The Harvard Center convened an expert panel to help guide the process and advise on evaluation of the scientific literature. The overall decision-analytic approach was to identify the important health effects, assess the dose–response relationships between fish consumption (or a constituent) and each health outcome, and then to synthesize these dose–response relationships into an overall model of health effects.

An introductory article “Health Trade-offs from Policies to Alter Fish Consumption” by Steven M. Teutsch, MD, MPH, Merck & Co., Inc., West Point, Pennsylvania; and Joshua T. Cohen, PhD, Harvard Center for Risk Analysis, Boston, Massachusetts, discusses the overall rationale for the project and why the decision analytic approach it illustrates is critical. They point out that although there is a substantial literature on the risks and benefits of fish consumption, important gaps remain. Despite these gaps, decisions about how to deal with tradeoffs must be made based on what we know now. The authors explain that “Decision analysis is an important tool that can quantitatively synthesize disparate information and assess the impact of uncertainty on our conclusions.”

In “A Quantitative Analysis of Fish Consumption and Stroke Risk” by Colleen Bouzan, MS, Joshua T. Cohen, PhD, William E. Connor, MD, Penny M. Kris-Etherton, PhD, George M. Gray, PhD, Ariane König, PhD, Robert S. Lawrence, MD, David A. Savitz, PhD, and Steven M. Teutsch, MD, the authors conclude that “any fish consumption confers substantial relative risk reduction compared to no fish consumption, with the possibility that additional consumption confers incremental benefits.”

Turning attention to coronary heart disease, the article “A Quantitative Analysis of Fish Consumption and Coronary Heart Disease Mortality” by Ariane König, PhD, Colleen Bouzan, MS, Joshua T. Cohen, PhD, William E. Connor, MD, Penny M. Kris-Etherton, PhD, George M. Gray, PhD, Robert S. Lawrence, MD, David A. Savitz, PhD, and Steven M. Teutsch, MD, shows “that consuming small quantities of fish is associated with a 17% reduction in CHD mortality risk, with each additional serving per week associated with a further reduction in this risk of 3.9%.”

In some cultures, fish is known as “brain food.” In the article, “A Quantitative Analysis of Prenatal Methyl Mercury Exposure and Cognitive Development” by Joshua T. Cohen, PhD, David C. Bellinger, PhD, and Bennett A. Shaywitz, MD, the authors examine the negative cognitive effect of MeHg exposure. Although the effects they observed were small on an individual level, they suggest that “Ultimately, the importance of a shift in IQ due to MeHg exposure lies in its aggregate impact on the population. While not noticeable in an individual, subclinical effects can be large when summed over the population. Our purpose in estimating the magnitude of this effect is to compare its aggregate impact to the aggregate impact of other subtle effects associated with changes in fish consumption.”

Some positive cognitive effects of fish consumption can be found in a study, “A Quantitative Analysis of Prenatal Intake of n-3 Polyunsaturated Fatty Acids and Cognitive Development” by Joshua T. Cohen, PhD, David C. Bellinger, PhD, William E. Connor, MD, and Bennett A. Shaywitz, MD. Although the effects, like those of MeHg, were small on the individual level, the authors conclude, “Nonetheless, the estimates developed here serve as a useful starting point for the purpose of quantitatively evaluating the cognitive benefits of maternal fish consumption, so that these benefits can be compared to the attendant risks resulting from prenatal exposure to mercury.”

“A Quantitative Risk–Benefit Analysis of Changes in Population Fish Consumption” by Joshua T. Cohen, PhD, David C. Bellinger, PhD, William E. Connor, MD, Penny M. Kris-Etherton, PhD, Robert S. Lawrence, MD, David A. Savitz, PhD, Bennett A. Shaywitz, MD, Steven M. Teutsch, MD, and George M. Gray, PhD, synthesizes the results of these four contributions, weighs the positive and negative effects, and discusses a range of appropriate public health recommendations.

In addition, two commentaries take a somewhat broader view of the issues. “Fish, Health, and Sustainability,” by Anthony J. McMichael and Colin D. Butler, of the National Centre for Epidemiology and Population Health, Australian National University, Canberra, Australia, looks at potential consequences of changes in diet on a global scale. They caution, “The well-informed fish consumer of the future may wish to consider not only the likely MeHg and PUFA concentration of her meal, but its ecologic impact and – perhaps – whether his/her use of market power could unintentionally harm the health of others.”