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Mercury in fish and cardiovascular disease


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Eat lots of fatty fish to stay healthy, we are told, but what about the Mercury!

Funny you should ask - some small studies identified Mercury in fish as a problem for your heart, other small studies found Mercury was not a problem for your heart.

The problem is that small studies may just have got a result by chance.

What to do - run a big study!

(Do not try this at home.)

  • Take 173,229 people, average age 61 (men) and 54 (women).
  • Give questionnaires and take toenail clippings every two years.
  • Follow them for 11 years.
  • Identify 3427 who had cardiovascular disease (coronary heart disease and stroke).
  • Match them as closely as possible with 3427 people with no cardiovascular disease (same age, sex, race, and smoking status).
  • Look at the highest 20% mercury scores and the lowest 20% mercury scores.
  • See how this matches cardiovascular disease risk.

Turns out those with the highest mercury levels in their bodies (toenails are a good measure) had:

  • Lower risk of coronary heart disease
  • Lower risk of stroke
  • Lower total risk of cardiovascular disease

The risks were not greatly lower - so don't go out seeking mercury for heart health.

But it does show Mercury is NOT a problem for the heart.

Wildly speculating as to the possible cause of this result, I think that most of that extra mercury in the blood of the heart-healthy people may have come from eating fish - our highest source of mercury in the diet.

And we know that the fat in fish protects the heart.

So it looks to me like this study might suggest that if there is any minor problem with eating the mercury in fish it is overwhelmed by the benefit from the fish itself.

N Engl J Med. 2011 Mar 24;364(12):1116-25.

Mercury exposure and risk of cardiovascular disease in two U.S. cohorts.

Mozaffarian D, Shi P, Morris JS, Spiegelman D, Grandjean P, Siscovick DS, Willett WC, Rimm EB.


Division of Cardiovascular Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, USA. dmozaffa@hsph.harvard.edu



Exposure to methylmercury from fish consumption has been linked to a potentially increased risk of cardiovascular disease, but evidence from prior studies is equivocal. Beneficial effects of the ingestion of fish and selenium may also modify such effects.


Among subjects from two U.S. cohorts (a total of 51,529 men and 121,700 women) whose toenail clippings had been stored, we prospectively identified incident cases of cardiovascular disease (coronary heart disease and stroke) in 3427 participants and matched them to risk-set-sampled controls according to age, sex, race, and smoking status. Toenail mercury and selenium concentrations were assessed with the use of neutron-activation analysis. Other demographic characteristics, cardiovascular risk factors, fish consumption, and lifestyle habits were assessed by means of validated questionnaires. Associations between mercury exposure and incident cardiovascular disease were evaluated with the use of conditional logistic regression.


Median toenail mercury concentrations were 0.23 μg per gram (interdecile range, 0.06 to 0.94) in the case participants and 0.25 μg per gram (interdecile range, 0.07 to 0.97) in the controls. In multivariate analyses, participants with higher mercury exposures did not have a higher risk of cardiovascular disease. For comparisons of the fifth quintile of mercury exposure with the first quintile, the relative risks were as follows: coronary heart disease, 0.85 (95% confidence interval [CI], 0.69 to 1.04; P=0.10 for trend); stroke, 0.84 (95% CI, 0.62 to 1.14; P=0.27 for trend); and total cardiovascular disease, 0.85 (95% CI, 0.72 to 1.01; P=0.06 for trend). Findings were similar in analyses of participants with low selenium concentrations or low overall fish consumption and in several additional sensitivity analyses.


We found no evidence of any clinically relevant adverse effects of mercury exposure on coronary heart disease, stroke, or total cardiovascular disease in U.S. adults at the exposure levels seen in this study. (Funded by the National Institutes of Health.). PMID: 21428767

This extract can be found on http://PubMed.com, and is in the public domain.On PubMed.com there will be a link to the full paper (This time free).Any highlighting (except the title) is not by the author, but by Jim Marshall.Jim is not a doctor.

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