WEDNESDAY, March 23 (HealthDay News) -- Though repeatedly linked
to neurological deficits in children and unborn babies, Americans'
level of exposure to mercury from sources such as fish is not
associated with a higher risk of heart disease, stroke or other
cardiovascular disease, a new study suggests.
Building on prior research that produced inconsistent results,
scientists from Harvard School of Public Health and Brigham and
Women's Hospital in Boston evaluated data from two separate studies
on more than 173,000 men and women who answered questions about
their medical history, risk factors, disease incidence and
The researchers also measured mercury concentrations in the
stored toenail clippings -- a reliable storehouse of long-term
mercury exposure -- of nearly 7,000 participants, an equal number
of whom had or had not suffered a cardiovascular event during the
study follow-up period.
The team found no sign that the mercury levels hiked
"Basically, what we found was very simple and very clear," said study author Dr. Dariush Mozaffarian, an associate professor of epidemiology at Harvard School of Public Health and division of cardiovascular medicine at Brigham Women's Hospital and Harvard Medical School.
"I think this is the most definitive study, and I'm not sure more studies are actually needed," Mozaffarian added. "It's nice to be able to answer an important research question. This is observational, so there's possibly some subtle effect we missed. But I think this provides the most definitive evidence available."
The study, which was funded by the U.S. National Institutes of
Health, is published March 24 in the
New England Journal of Medicine.
Health experts have long advised the public to balance the
health benefits of fish (which often contains healthy omega-3 fatty
acids) with the potential of mercury exposure from doing so. Also
known as methylmercury, the heavy metal settles into bodies of
water and can be absorbed by various species of fish, according to
the U.S. Environmental Protection Agency.
Some fish, such as swordfish, tilefish and king mackerel, tend
to store more of the toxin in their flesh. Due to the risk for
neurodevelopmental issues, the U.S. Food and Drug Administration
has long advised pregnant women, women who may become pregnant,
nursing mothers and young children to limit their intake of these
and other fish and shellfish.
Among study participants in the top 20 percent of mercury
exposure, average toenail mercury levels measured 0.7 micrograms
per gram. Current U.S. advisories for sensitive subgroups aim at
keeping mercury exposure below a level correlated with toenail
levels of 0.4 micrograms per gram.
Not only was no link between mercury and higher cardiovascular
disease found, the study said, but participants with higher mercury
levels actually experienced slightly lower heart disease rates.
Mozaffarian and his team attributed this to the other beneficial
effects of fish consumption.
The authors noted that their research should not change
advisories for eating fish with higher mercury levels among women
who are or may become pregnant.
"There is no strong or moderate evidence that mercury has any effects in adults," Mozaffarian said. "So it's important and helpful that people can feel comfortable with fish as a normal part of their diet."
"It doesn't mean we can stop worrying about mercury in the environment," he added. "But for the individual consumer making a decision about eating fish, they can take this worry off the table."
One expert agreed that the study shouldn't cause Americans to
feel any easier about mercury in the environment.
Elena Craft, a health scientist at the Environmental Defense
Fund, acknowledged that the study looks at a much larger sampling
than prior research.
"But for me, it doesn't alter the primary health concerns about mercury exposure -- the neurobehavioral effects on children and developing fetuses," Craft said. "That's always been the most sensitive endpoint. In some ways, it's an interesting study, but in regards to protecting public health it just doesn't alter that bottom line."
For guidelines on mercury in fish and shellfish, visit the
U.S. Food and Drug Administration.
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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