The Doctors Are In. the Jury Is Out.
[Rachel's Introduction: It is "very unwise to wait until we have complete scientific truth" and the "prudent judgment is to protect human health."]
Author Name: 
By Clark Hoyt
Philippe Grandjean is adjunct professor of environmental health at Harvard University's School of Public Health and chairman of the department of environmental medicine at the University of Southern Denmark. Dariush Mozaffarian is assistant professor of epidemiology at the Harvard School of Public Health.

Both agree that fish -- the right kind in the right amounts -- is good for you. Both agree that mercury is harmful to the neurological development of unborn and young children, and both support the government's 2004 recommendation that pregnant women, women who might get pregnant, nursing mothers and young children limit their consumption of fish and avoid certain types known to be high in mercury.

But they come at the issue with a strikingly different emphasis.

Each was quoted in a January 23 New York Times article about mercury in tuna sushi, and I thought it would be useful to readers to hear what they have to say at greater length.

What follows is a link to an interview Mozaffarian gave to Time.com on the day after the Times article and answers that Grandjean sent to questions I asked after reading Mozaffarian's interview with Time and talking with him.

Q and A with Philippe Grandjean:

Q: You told The Times that, "The current advice from the F.D.A. is insufficient." Would you elaborate? In what way is it insufficient?

What advice do you believe the government should give consumers regarding tuna and/or the consumption of fish in general?

A: I support the recommendation to eat fish for dinner once or twice per week for the sake of important nutrients. However, I would advise against eating seafood high in mercury due to the risk of toxicity. At best, the mercury may cancel out the benefits from fish. If you eat fish high in mercury and low in n-3 fatty acids -- such as bluefin tuna -- then the balance has tilted, because bluefin tuna has a very high mercury concentration and only little n-3.

International and national agencies have examined the mercury literature and reached the conclusion that mercury in seafood represents a risk, especially to pregnant women and children. They have therefore recommended to keep mercury intakes at safe levels, i.e. below the US EPA's reference dose or some other value like that.

Although recent research has shown that these limits may be too high and do not provide the protection originally stated, I would support the EPA limit as appropriate and well documented. The trouble is that it can be difficult to respect this limit while also eating fish dinners and trying to get enough n-3 (without taking fish oil caps). As a rough calculation, if you want to respect the EPA mercury limit and still want to eat 400-500 grams of fish per week, then the mercury concentration in the fish should average no more than 0.1 ppm.

The FDA has many years ago fixed a limit for mercury in fish at 0.5 ppm. This limit was essentially based on what was achievable, and for large (predator) fish, a limit of 1 ppm was decided, simply to avoid having to reject too much fish from the market. The limit is not based on health risks. The problem is that eating fish for dinner at high but legal levels can exceed the EPA limit.

The two agencies have worked out a compromise recommendation of limits to how much fish one can eat of one kind or another. This advice is complicated for the average consumer, and the EPA limit will easily be exceeded anyway. My advice is simple: Eat smaller fish (sardines!) that are low in the food chain (avoid those that eat other fish) and have been caught in unpolluted waters (respect the state fishing advisories).

I would have preferred if the FDA would tell the consumers which fish contain very little mercury and can be eaten for dinner twice per week or even more. Salmon is such a fish that contains very little mercury and has a high content of n-3, and it is superb for sushi in my opinion. I would emphasize the positive aspects and point to the kinds of fish that are safe.

Q: Your Harvard colleague, Dr. Dariush Mozaffarian, told Time magazine that the E.P.A.'s acceptable limit for mercury includes a 10-fold safety factor, so that, for example, if six pieces of tuna sushi a week put you at the limit, you would have to eat 60 a week to get to a level where the E.P.A. determined that risk was occurring. Do you agree with that characterization? If not, how would you characterize the limit?

A: This is a misunderstanding. The EPA reference dose (as approved by experts of the National Academy of Sciences) was arrived at by first calculating a so called benchmark dose that statistically is associated with a small, but detectable adverse effect. Dr. Mozaffarian is assuming that the benchmark dose is "safe," but is not. Research has clearly showed adverse effects below this level. According to EPA's procedures, this benchmark dose is then divided by 10 to arrive at a limit that can be considered safe. This factor of 10 is also meant to take into account differences in sensitivity (because the statistical calculation of the benchmark dose assumes that all people are equally sensitive, which they are not). WHO used a similar procedure but reached a limit that is twice as high. More recent research suggests that both limits are too optimistic and that mercury is more toxic that previously thought. The WHO limit is for weekly intakes, which I think is better than having a limit for daily intake, since the critical factor is the long-term exposure.

Q: Dr. Mozaffarian said that the dangers of not eating fish, including tuna, outweigh what he called "the small possible dangers from mercury." What would you say?

A: I agree that there are nutritional advantages of eating fish, but tuna is not a good source of essential nutrients such as n-3 fatty acids. The mercury content can easily outweigh the advantages. I would not call the dangers from mercury small. Mercury is toxic to brain development and is therefore a danger to pregnant women and children. In non-pregnant adults, mercury very likely contributes to the development of heart disease.

Q: Is it correct that the existing government limits were determined with women of child-bearing age, pregnant women, nursing women and young children in mind? Does that mean that others are at less and perhaps little or no risk when mercury levels are higher than the government standard?

A: Yes, the existing limits were developed to protect the most sensitive populations you mention. In addition, we are all at risk of developing heart disease, and current evidence suggests that it would be wise to limit our mercury intake at a similar level.

Q: You told The Times that it is "very unwise to wait until we have complete scientific truth" and that the "prudent judgment is to protect human health." For a lay audience, how would you characterize the state of science with regard to the health effects of mercury at levels such as those found in the samples of tuna tested for The Times?

A: In science, we like to have our hypotheses verified by repeated studies and replications, before we can say that we have the proof. In regard to a public health hazard, we rarely have the luxury of time. It would be unethical for us to allow an almost certain toxic hazard, while we study how it impacts on brain development in children or causes heart disease in adults. We therefore have to strike a balance, where we protect public health but don't overreact to the smallest warning signals. In the EU, this is called the "precautionary principle." In regard to mercury, decades of research have documented adverse effects even at very low exposures. This is now widely accepted, and the UN Environment Program obtained consensus between 140 countries that mercury pollution is an international problem that must be combatted. In regard to the mercury in tuna tested by the NYT, I would say that there is little hazard if you do this once or on a very rare occasion. But if you include tuna sushi in your diet on a regular basis, say once a week, then we have ample scientific support to say that can result in adverse effects. Tuna is low in n-3 fatty acids, so there is no nutritional advantage, thus emphasizing the toxic risk.

Q: I am struck by the apparent differences in how two highly respected medical researchers see this issue, and I think it presents an interesting challenge for a general circulation newspaper like The Times. The broad question is what should a newspaper say to properly inform its readers so they can make intelligent decisions?

A: I think the contrast appears because Dr. Mozaffarian and other respected colleagues speak from a nutrition standpoint. I certainly agree that fish can be a healthy component of a balanced diet. Just like water or vegetables. But that does not mean that we should favor contaminated water or vegetables, or fish for that matter. I think the misunderstanding comes from the failure to recognize that fish and seafood constitute a highly varied food source. Some types are high in nutrients while low in mercury, and they should be favored. FDA and the nutritionists should help us making the wise choice instead of trying to explain away a toxic pollutant. In plain terms, switch to salmon sushi and serve sardines as hors d'oeuvre.

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