Fish: Balancing Health Risks and Benefits

Fish
Balancing Health Risks and Benefits

Walter C. Willett, MD, DrPH

In this issue of the American Journal of Preventive Medicine, Teutsch, Cohen, and their colleagues1-6 present a detailed analysis of possible health effects from policies to alter fish consumption, which have both potential harms and benefits. As they clearly document, the results would have overall benefits under optimistic scenarios in which women who may become pregnant replace fish high in mercury with low-mercury fish, or in which there is an increase in low-mercury fish in the general population. However, the overall consequences could be adverse if fish consumption is reduced in the general population, which had apparently occurred. This analysis supports current guidelines that focus on changes in the type of fish eaten by women in the reproductive age, but also highlights concerns that educational messages and the implementation of policies must be carefully crafted to avoid unintended consequences.
The recent decreases in fish consumption have probably been influenced by not only fears about mercury, but also by a widely publicized report in a prominent journal7 that farmed salmon contains measurable amounts of organochloride compounds. That publication was particularly troublesome, perhaps even irresponsible, because the implied health consequences were based on hypothetical calculations and very small (lifetime risks of ≤1:10,000). In contrast, the benefits of eating salmon are based on human data at the doses actually consumed and, as pointed out by Cohen et al.2 in the present analysis, are likely to be at least 100-fold greater than the estimates of harm, which may not exist at all. Because the report on organochloride consumption almost certainly contributed to a reduction in fish consumption, that publication likely caused substantial numbers of premature deaths. Although the monitoring of contaminant levels in foods is an important function, reports of findings in places where widespread publicity is likely should be accompanied by at least a qualitative balancing of likely risks and benefits of changing consumption of the foods being considered. A more detailed analysis such as that by Cohen et al.2 would be even better.
 The nutritional, environmental, and policy issues surrounding consumption of fish and omega-3 fatty acids extend well beyond the scope of the analysis conducted by Cohen at al.6 Catches of wild fish are presently near maximum, and perhaps even greater than sustainable, so further increases in fish consumption will need to be mainly from aquaculture. This method of production has many potential environmental impacts , but is worthy of careful development because conversion of feed to protein is far more efficient for fish than for land animals (because fish are cold blooded and float, no energy is needed to maintain body temperature and little is needed for movement). However, on a global basis, even larger increases in aquaculture are unlikely to meet the needs for omega-3 fatty acids, because for a large part of the world’s population, including Russia and much of Eastern, Europe, per capita fish intake is extremely low. Thus, for much of the world, omega-3 fatty acids will need to be obtained from other sources. Fortunately, plant sources are many (as

the 18-carbon fatty acid, alphalinoleic acid),including soybean and canola oils. However, in the United States and many other countries, the partial hydrogenation of these oils destroy the omega-3 fatty acids so that intake of these essential fatty acids is very low. In such regions, the most rapid way to increase consumption of omega-3 fatty acids is to stop the partial hydrogenation of these oils, which would also virtually eliminate the consumption of trans-fatty acids. Whether alpha-linoleic acid, through endogenous conversion to EPA and DHA, can provide all the health benefits of fish oil is a research topic of great importance. This has potential implications for the analyses of Cohen at al.,1-6 because the background intake of alpha-linoleic acid is likely to be increasing in the United States due to reductions in partial hydrogenation of soybean oil, the benefits of fish intake may decrease. As our food supply is dynamic and human nutrition is complex, risk-benefit analysis cannot be static.
 Fish consumption is but one example in human nutrition where potential competing risks and benefits exist; dairy products provide another. The recent U.S. dietary guidelines8 recommend that all persons increase consumption of milk, or equivalent dairy products, to three glasses per day. The recommendation, if implemented, would lead to radical changes in individual diets, average consumption by adult men is presently less than one serving per day. It would also result in a doubling of milk production in the United States, which would have major economic and environmental consequences. The recommendation was not based on evidence that there would be an improvement in human health if everyone consumed three glasses of  milk per day, but rather on the mandate by the U.S. Department of Agriculture that the guidelines should meet the dietary reference intakes (DRIs) for calcium, potassium, and other nutrients from food sources alone. The DRIs in turn are also not usually based on health outcomes, but rather on a single metabolic criterion, such as the short-term maximal calcium retention test. The health consequences of high consumption of dairy products are complex and not fully understood. For example, although some intake of calcium is essential, high milk consumption has consistently not been associated with low risk of fractures in large prospective studies, whereas increased risks of advanced or fatal prostate cancer have been observed in many studies. Moreover, large amounts of saturated fat would be introduced into the food supply if dairy consumption were doubled, even though the recommendation is to consume low-fat dairy products.
 Interestingly, detailed economic analysis are required for government regulatory actions, but comparable analysis of health risks and benefits are not, even for the dietary guidelines, which have huge policy implications for government food programs. The field of nutrition would benefit from further work like that of Cohen et al.1-6

1. Teutsch SM, Cohen JT. Health trade-offs from policies to alter fish consumption. Am J. Prev Med 2005;29:324.

2. Cohen JT, Bellinger DC, Connor WE, et al. A quantitative risk-benefit analysis of changes in population fish consumption. Am J Prev Med 2005;29:325-34.

3. Konig A, Bouzan C, Cohen JT, et al. A quantitative analysis of fish consumption and coronary heart disease mortality. Am J Prev Med 2005;29:335-46

4. Bouzan C, Cohen JT, Connor WE, et al. A quantitative analysis of fish consumption and stroke risk. Am J Prev Med 2005;29:347-52.

5. Cohen JT, Bellinger DC, Shaywitz BA. A quantitative analysis of prenatal methyl mercury exposure and cognitive development. Am J Prev Med 2005;29:353-65.

6. Cohen JT, Bellinger DC, Connor WE, Shaywitz BA. A quantitative analysis of prenatal intake of n-3 polyunsaturated fatty acids and cognitive development. Am J Prev Med 2005;29:366-74.

7. Hites RA, Foran JA, Carpenter DO, Hamilton MC, Knuth BA, Schwager SJ. Global assessment of organic contaminants in farmed salmon. Science 2004;303:226-9.