5 November 2002
you eat a lot of fish, you may run health risk
Anita Manning, USA TODAY
Americans have been told repeatedly that fish is good for the heart
and the waistline. But there is growing concern that some seafood
lovers are consuming high doses of mercury along with their fish
dishes and could be suffering health problems as a result.
of childbearing age have long been warned to limit their fish intake
to reduce the risk of exposing an unborn baby to mercury. But in
new study, a San Francisco physician says she discovered high
levels of toxic mercury, called methylmercury, in blood and hair
samples taken from dozens of her patients — men, women and
most common sources of mercury in air are coal-burning power plants,
municipal waste combustors, medical waste incinerators and hazardous
can contaminate water or land through the discharge of industrial
particles of mercury travel through smokestacks into the air. They
then fall onto soil or water.
can accumulate in fish and wildlife. Small fish are eaten by big
fish and fish-eating birds generally have higher levels of contamination.
were suffering symptoms associated with low-level mercury poisoning,
including hair loss, fatigue, depression, difficulty concentrating
and headaches. The implication, she says, is that anyone who consumes
a lot of fish, especially large steak fish such as swordfish and
shark, could be at risk.
have people who have been told to eat fish because it's healthful,
but they have not been told it contains contaminants," says
physician Jane Hightower, whose yearlong study of patients in her
Bay Area practice was published Friday in Environmental Health Perspectives,
an online journal of the National Institute of Environmental Health
Services, part of the National Institutes of Health.
Food and Drug Administration advisory committee recommended in July
that the agency do research to assess the risks to women and young
children who eat canned tuna. The amount of methylmercury per can
is generally low, about 0.17 parts per million, but it can vary
widely, says Michael Bender of the Mercury Policy Project, an advocacy
is the most consumed fish in the country," Bender says. "If
you're a pregnant woman and you eat over two cans of tuna per week,
you can go over" safe levels of mercury. The FDA currently
recommends that women who are or could become pregnant limit all
fish to 12 ounces a week.
survey of Hong Kong high school students found that as many as 10%
eat enough fish to exceed safety limits for mercury exposure. The
report, which prompted a Chinese government warning about consumption
of shark and other large fish, found that the students' diets gave
them a mercury exposure of 6.41 micrograms per kilogram (2.2 pounds)
of body weight a week. The World Health Organization recommends
a 5-microgram limit.
September, the United Nations Environment Programme hosted a meeting
in Geneva about ways to reduce mercury emissions around the world.
A report from that meeting will be considered by environment ministers
at a meeting of UNEP's governing council in February and could lead
to consideration of an international treaty on mercury emissions.
study and similar reports from other researchers who attended a
recent meeting in Vermont, sponsored by the EPA, suggest that consumers
who eat expensive fish are increasingly putting themselves at risk
for mercury poisoning.
1 can or 6 oz
much is safe?
amount of canned tuna* that is safe to eat each week should
be based on body weight
Fish Facts for Good Health, publication of the Washington
Department of Health.
are switching to fish to improve their health," says Caroline
Smith DeWaal of the Center for Science in the Public Interest, but
"they're being exposed to dangerously high levels of methylmercury."
That's especially troubling if the consumers are women who plan
to have children, says DeWaal, author of the recently published
Is Our Food Safe? "It is critical that women of childbearing
age stop eating this fish from six months to a year before becoming
Centers for Disease Control and Prevention estimates about 8% of
women in this age group have enough mercury in their bodies to pose
a risk of having babies with mild learning problems.
released from power plants, municipal waste facilities and medical
incinerators is the primary source of methylmercury in fish. Methylmercury
is an organic form of mercury that is different from what is in
mercury thermometers or what goes up smokestacks when coal is burned.
is converted to methylmercury by bacteria in water. So when people
are talking about mercury in fish, they are really talking about
the toxic methylmercury. What makes it dangerous to health is that
it is hard for the body to eliminate, so it can build up and may
affect the nervous system. Most human exposure to methylmercury
is through fish consumption.
FDA ceased its large methylmercury sampling program in 1998, and
today federal agencies conduct only limited testing of fish for
methylmercury. The industry does, too, on a voluntary basis, says
Rhona Applebaum, a scientist with the National Food Processors Association.
"Whether it's mercury or any other defect, chemical or microbial,
the industry does regular testing" to assure that the product
meets FDA standards.
do know tuna contains methylmercury," she says, but mercury
is "naturally occurring, so on a daily basis people are exposed.
It's not at levels that will result in acute toxicity unless people
are not practicing basic tenets of nutrition: balance, variety and
show women ages 15-44 eat canned tuna 1.5 times a month, well within
the range of safety, but too much of anything can be harmful, she
says. "If people are going to consume one type of food literally
ad nauseam, there's going to be an impact."
FDA and Environmental Protection Agency differ on what they consider
acceptable levels and measure it differently. The FDA, which regulates
commercially caught fish, sets an "action level" of 1
part per million. If higher levels are reported, the FDA can remove
the fish from the market, though critics say that rarely occurs.
The EPA has a "reference dose" that says people can be
exposed to .1 microgram per kilogram of body weight per day, which
is roughly 5 to 7 micrograms per day for someone who weighs 100
to 154 pounds, says Kate Mahaffey of the EPA. That's about a fifth
of the amount the FDA considers safe.
FDA's standard permits about 480 micrograms of methylmercury in
one pound of fish, she says. "If fish is that contaminated,
and you're trying to keep in the 5 to 7 micrograms per day range,
you can't eat much of that fish."
the EPA does not regulate commercial fish. It works with state environmental
and health departments to test local rivers and other bodies of
water where recreational fishing is done and where mercury levels
may be high because of local pollution. When high levels of mercury
are detected in the water, the states post fish advisories to warn
are fish advisories in most states for mercury," says Michael
Gochfeld, professor of environmental medicine at the Robert Wood
Johnson Medical School in Piscataway, N.J.
in areas where industrial pollution has been reduced, the problem
persists because of atmospheric pollution drifting from other areas,
he says. "Virtually all our mercury-polluting industry in New
Jersey is closed," he says, but state health officials regularly
warn residents not to eat fish from specific lakes and rivers where
mercury levels are high. Ten states also warn pregnant women to
limit consumption of canned tuna and other commercial seafood.
health experts point out that fish is an important part of a balanced
diet. It's full of vitamins and other nutrients, including omega-3
fatty acids, which help lower cholesterol and blood pressure and
reduce the risk of cardiac arrest. And it's low in calories.
fish should you eat?
Fish Facts for Good Health, publication of the Washington Department
high levels of mercury:
that have generally
levels of mercury:
that squares with mercury poisoning is "a very difficult
message to convey," says epidemiologist Tom Sinks of the
National Center for Environmental Health, part of the CDC. "Fish
is a vehicle by which people are exposed to mercury. But at the
same time, fish is a good source of protein and nutrients, an
important part of the diet, and one we want people to eat in a
says the fish that are high in omega-3, such as salmon and sardines,
are low on the mercury scale. "We want to encourage people
not to avoid fish, but to advise them that some fish have higher
levels of mercury, and if they're concerned, they should avoid
those fish," he says.
trouble, Hightower says, is that some people appear to be more
sensitive to methylmercury than others. The EPA and the National
Academy of Sciences recommend keeping mercury levels in blood
at 5 micrograms per liter or less. In Hightower's study, patients'
blood levels ranged from 2 to nearly 90 micrograms per liter.
Symptoms varied widely and did not always correlate with the burden
were some with elevated levels who had no symptoms. There are
some with low levels with symptoms," she says. "It is
unclear whether these patients are having symptoms due to direct
effects of mercury or a reaction to it," she says. But, she
adds, most people can withstand a bee sting, while others go into
shock. "We recognize there are severe reactions to very minuscule
quantities of certain agents."
says it's not known how many people might be affected by methylmercury,
and she can't prove that the symptoms her patients suffered were
caused by overconsumption of fish, but "the funny thing is,
people got better when they stopped eating it."
what happened to Wendy Moro, 40, a marketing consultant who lives
with her husband and son in a suburb of San Francisco. Until April
2001, she says, she was the picture of health. A 110-pound bundle
of energy, she ran several miles a day, danced ballet, lifted
weights. She also ate fish two to five times a week, at home and
at the Bay Area's better restaurants.
the West Coast, we eat a lot of fish," she says. "It's
an affluent community, and fish is accessible and popular. You
go out for dinner. People don't go out for T-bone steaks anymore.
It's all fish."
ate tuna for lunch a couple of times a week, and the family would
have seafood for dinner regularly, often choosing steak fish such
as ahi tuna or halibut. "We just looked for what was fresh,"
she says. "I thought I was being really healthy, not eating
meat, eating lots of fish."
first sign of trouble was severe fatigue — "the kind
where it is impossible to stay awake for more than a few hours
at a time," she says. Then pain and weakness in her limbs
worsened to the point where she could barely stand. A series of
doctors diagnosed or tested her for multiple sclerosis, muscular
dystrophy, chronic fatigue syndrome, mononucleosis, diabetes insipidus.
One suggested she be evaluated for mental illness.
she was referred to Hightower, who tested her for mercury poisoning.
Moro's blood level was 17, more than three times the recommended
level, though still below what some doctors think is enough to
cause such severe symptoms.
Moro stopped eating fish, her symptoms began to disappear. Now,
she says, she's "about 85%" back to normal. She keeps
a file on mercury that she gives to friends who are thinking about
having a baby.
it could happen to her, it could happen to anyone, she says. "I'm
such an average Jane. I live in a suburb; I have 1.5 kids, if
you count my dog. I'm not a super-fanatic, not a triathlete. I'm
not super-rich or poor. I'm just an average Joe-USA TODAY. That's
Stern, chief of the New Jersey Department of Environmental Protection
who served on a National Academy of Sciences committee on methylmercury
two years ago, says it's too soon to draw firm conclusions from
Hightower's study. "I would consider it to be the very early
stages of a clinical case description, and it's not at a point
yet where it can be translated into a public health message,"
reports, he says, "call our attention to the potential of
health effects at low levels of exposure (to methylmercury), but
they don't make an open-and-shut case."
the relief of symptoms reported by people who stop eating fish
is inconclusive, he says, because it is "hard to distinguish
that from a placebo effect. From an objective standpoint, one
cannot say this association goes to the next step of cause and
if nothing else, Stern says, consumers and doctors should be alert
to the possibility that small exposures to mercury in fish might
cause symptoms. His cautionary conclusion: "Individuals should
choose their diets wisely."