JM. 2003. Mercury Levels in High-End Consumers of Fish.
Francisco Chronicle coverage
Jane Hightower reports that patients in her medical practice in
the San Francisco Bay Area who consume large predatory fish like
tuna and swordfish carry high levels of methylmercury in their blood
and/or hair and are likely to report various medical symptoms consistent
with low-level mercury poisoning. The good news is that
when they stopped eating fish contaminated with mercury, their blood
mercury levels went down over a period of 20+ weeks. For
the most part these patients were socially and economically advantaged
people for whom cost was not an issue in determining what fish to
did she do? Hightower interviewed patients on patterns
of fish consumption and also about other sources of mercury exposure
(mecury amalgam fillings, thimerosal in vaccinations). Those whose
fish diet indicated a possibility of high mercury exposure were
then asked to participate in a study that involved sampling blood
or hair mercury levels over time, during which they were also encouraged
to lower their predatory fish consumption.
did she find? Approximately 140 out of 720 patients surveyed
had fish consumption patterns suggesting high mercury exposure.
Of these 116 allowed blood measurements; another with 7 allowed
hair analysis. Mercury averaged 14 µg/L in serum. Hair levels
ranged from 1.55 to 14.81 µg/g. EPA and the National Academy
of Sciences recommend not allowing mercury levels to rise above
5 µg/L and hair not above 1 µg/g. Four of Hightower's
patients had blood levels in excess of 50 µg/g.
from eighty-nine patients were put through more detailed statistical
analysis to look for relationships among fish consumption patterns
and mercury level. Among these patients, mercury ranged from 2 to
89.5 µg/L, with a mean of 14.5 µg/L. 82 subjects
had levels above 5 µg/L and sixteen subjects had levels above
20 µg/L. The estimates of fish consumption were based
on questionnaire responses about past histories and therefore subject
to considerable uncertainty. The only strong pattern revealed by
this analysis was for swordfish: the more frequently a patient ate
swordfish, the higher their mercury levels.
tracked 67 patients over time to see if reducing fish consumption
reduced mercury levels. As evident in the graph below, all but two
of these patients reduced their levels to under 5 µg/L after
41 weeks; the two exceptions continued to eat large predatory fish.
mercury levels in patients after beginning a diet with reduced
predatory fish intake. Two patients did not comply fully.
does it mean? The bad news is that some of the fish currently
consumed by Americans is sufficiently contaminated by mercury to
elevate levels far beyond thresholds of concern. This is not a new
story. The twist that attracted media
attention to Hightower's research is that her patients tend
to come from tonier economic backgrounds and many are eating fish-rich
diets because they thought it was good for them.
does not expect her findings to be unique to the San Francisco area:
"It would be expected that places such as New York, Maine,
Florida, Hawaii, Martha’s Vineyard Massechusettes, and Los
Angeles, Monterey, Santa Cruz, San Diego, California could demonstrate
good news is that not all fish creates this risks, and that by avoiding
mercury-laden fish even people with high mercury levels can bring
them down (assuming no other sources).
tragedy is that we have allowed mercury to escape into the environment
which now means people must avoid important sources of protein.
This mercury comes from multiple sources, the most pervasive of
which is generation of electricity from coal contaminated by mercury.
The further tragedy is that we have the technology today
to be able to use coal without letting that mercury escape, but
the political process puts higher value on cheap electricity than
on avoiding neurological damage to children.
many other state agencies, Washington State's Department of Health
for limits to consumption of different type of fish because of mercury
contamination. For example, they would limit consumption of canned
tuna to 2 oz. per week for a child weighing 50 pounds.
That's one third of a can.