In response to Patty Young's query about fish oils, I would research
the issue of chemical contamination more thoroughly before advising
pregnant women to use them as supplements. Some studies show that
they are significantly contaminated with chlorinated pollutants.
Some of the contaminants found in fish oils, such as PCBs, are known
to act mimic the effects of lead in the prenatal brain. That is,
during the second trimester, exposures to even trace amounts can
interfere with brain cell migration and raise the risk for lowered
I.Q., learning deficits, attention problems, and delays in
psychomotor skills. PCB exposure during pregnancy interferes with
fetal thyroid hormone levels, which may be the mechanism by which
PCBs sabotage fetal brain growth and development.
I just finished a critical review of a pair of studies showing that
farmed salmon contain dioxin levels that are many times higher than
those found in wild salmon. The researchers, both in Canada and
Scotland, traced the problem back to fish oils added to commercial
salmon feed. These oils are are used to make farmed salmon grow
faster and reach market size sooner. Essentially, farmed salmon are
eating higher on the marine food chain than wild salmon and therefore
become more contaminated with persistent organic pollutants than
their counterparts in the wild.
While writing this review paper, I happened upon some other studies
that looked at fish oil contamination more directly, especially oils
intended as dietary supplements. I have NOT researched this topic at
all thoroughly so can't really answer any follow-up questions, but I
was curious enough to bookmark the abstract below.
You can research the topic by doing a medline search (try "Fish oils"
AND pesticides OR PCBs OR dioxins)
Here is the citation I saved:
journal: Chemosphere 1998 Oct-Nov;37(9-12):1709-21
title: Organochlorine residues in fish oil dietary supplements:
comparison with industrial grade oils.
authors: Jacobs MN, Santillo D, Johnston PA, Wyatt CL, French MC.
Department of Biology, University of Exeter.
Abstract: "The market for fish oils as dietary supplements is of
global importance. Although it is widely recognised that lipophilic
organic chemicals, particularly organochlorines, can accumulate in
fish oils, dietary supplements are not routinely considered when
estimating average daily intakes for these contaminants. This paper
reports levels of organochlorine residues in 44 fish
oils, collected from 15 countries between 1994 and 1995, including 38
purchased over the counter as dietary supplements. Despite controls
on the use of persistent organochlorine substances, appreciable
quantities are found in oils sold as dietary supplements. Levels are
discussed in relation to the significance of fish oil dietary
supplements as contributors to daily intake of PCBs and pesticide
residues."
If anyone is interested in my research commentary on farmed vs. wild
salmon, it will soon be published in the fall issue of The Ribbon,
which is the quarterly newsletter of the Program on Breast Cancer and
Environmental Risk Factors here at Cornell. Will be available on
line: http://www.cfe.cornell.edu/bcerf/
--
--
Sandra Steingraber, Ph.D.
Visiting Assistant Professor
Program on Breast Cancer and Environmental Risk Factors
110 Rice Hall
Cornell University
Ithaca, NY 14853
[log in to unmask]
www.steingraber.com
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