Fish Consumption, Methylmercury, and Human Heart Disease

Environmental mercury continues to be of concern to public health advocates, both in the U.S. and abroad, and new research continues to be published. A recent analysis of potential health benefits of reduced mercury emissions has opened a new area of public health concern: adverse effects on the cardiovascular system, which could account for the bulk of the potential economic benefits. The authors were careful to include caveats about the uncertainties of such impacts, but they cited only a fraction of the applicable health effects literature. That literature includes studies of the potentially harmful ingredient (methylmercury, MeHg) in fish, as well as of a beneficial ingredient, omega-3 fatty acids or “fish oils.” The U.S. Food and Drug Administration (FDA) recently certified that some of these fat compounds that are primarily found in fish “may be beneficial in reducing coronary heart disease.” This paper briefly summarizes and categorizes the extensive literature on both adverse and beneficial links between fish consumption and cardiovascular health, which are typically based on studies of selected groups of individuals (cohorts). Such studies tend to comprise the “gold standard” of epidemiology, but cohorts tend to exhibit a great deal of variability, in part because of the limited numbers of individuals involved and in part because of interactions with other dietary and lifestyle considerations. Note that eating fish will involve exposure to both the beneficial effects of fatty acids and the potentially harmful effects of contaminants like Hg or PCBs, all of which depend on the type of fish but tend to be correlated within a population. As a group, the cohort studies show that eating fish tends to reduce mortality, especially due to heart disease, for consumption rates up to about twice weekly, above which the benefits tend to level off. A Finnish cohort study showed increased mortality risks in the highest fish-consuming group (~3 times/wk), which had mercury exposures (mean hair content of 3.9 ppm) much higher than those seen in the United States. As an adjunct to this cursory review, we also present some new “ecological” analyses based on international statistics on hair Hg, fish consumption, other dietary and lifestyle factors, and selected cardiovascular health endpoints. We searched for consistent differences between primarily fish-consuming nations, like Japan or the Seychelles, and others who traditionally eat much less fish , such as in central Europe, for example. We use data on cigarette sales, smoking prevalence surveys, and national lung cancer mortality rates to control for the effects of smoking on heart disease. These ecological analyses do not find significant adverse associations of either fish consumption or hair Hg with cardiovascular health; instead, there is a consistent trend towards beneficial effects, some of which are