In an analysis of more than 1,600 men from Sweden
and Finland, researchers found that men with high levels of mercury in
the body had an increased risk of heart attacks, while those with a high
concentration of omega-3s had a lower risk.
Fish are considered part of a healthy diet,
but the balance between potential risks and benefits from the two
compounds is not clear.
study can't tease out cause and effect, researcher Maria Wennberg said
there are ways to get fish oil naturally without getting a lot of
"Fish consumption two
to three times per week, with at least one meal of fatty, non-predatory
fish (such as salmon) and an intake of predatory fish not exceeding
once a week can be recommended," Wennberg, of Umeå University in Sweden,
told Reuters Health by email.
fish such as shark, swordfish, king mackerel and tilefish are at the
top of the marine food chain and so concentrate mercury from the
environment in their tissues.
heavy metal is known to be toxic to the nervous system, especially in
fetuses and children, and the U.S. Environmental Protection Agency warns
women of childbearing age and children against eating predatory fish.
men in the new study, published in the American Journal of Clinical
Nutrition, submitted hair and blood samples to measure their mercury and
omega-3 levels, as well as information on their health and lifestyle.
average mercury level among the Swedish men was 0.57 micrograms per
gram of hair, whereas it was more than twice as high in their Finnish
peers. Swedes, however, had higher levels of omega-3s than did Finns.
researchers found that men with at least 3 micrograms of mercury per
gram of hair had a somewhat increased risk of heart attacks compared
with men with 1 microgram per gram, although they didn't calculate the
But this only held
true if the men also had low levels of omega-3 fats. For men with more
of the fats, it took higher levels of mercury to see an increased heart
attack risk - suggesting the two compounds might have opposite effects
on the ticker.
The results don't
prove that the high mercury levels were responsible for the increased
risk of heart attack, but merely that the two are linked.
Dariush Mozaffarian of the Harvard School of Public Health in Boston
said other factors, such as low education levels among those with high
mercury levels, could also be at work.
studies by Mozaffarian, who was not involved in the new work, did not
show a link between mercury and heart attacks. But that research
involved mercury levels much lower than in the current study.
Read the full story on the Reuters Website