I have been asked to explain the reported “findings” of the
SELECT study. This is the study generating new headlines claiming that fish oil supplements are linked to
an increased risk of aggressive prostate cancer.
For starters, the men in the SELECT study were not given
fish oil supplements. What the results were reporting were levels of EPA, DPA
and DHA omega-3s in blood, and cancer risk. And it is very important to note
that the difference of omega-3 levels when comparing the healthy (control)
group and the combined cancers group was nearly insignificant.
That difference is 4.66%
in the combined cancer group versus 4.48% in the control group. It is a minute variance. Eating one additional serving of fish compared to the control group could result in that difference. Again no fish oil supplements were
given in the study, so to blame omega-3 supplements for the reported findings
is totally irresponsible.
Another point to
consider is this. The reported omega-3
levels in any of the SELECT participants are not high levels. They are
only slightly higher than the levels in those who consume a western diet
typically average. Therefore any country that consumes a diet based on fish would
have incredibly high levels of aggressive prostate cancer, and that is not the
case.
What does the
science really say about fish consumption or omega-3 levels and risk of
prostate cancer?
The studies almost uniformly show that eating fish
or having higher plasma levels of omega-3 is protective. Several large scale epidemiological studies, including those looking
at native Japanese men, Inuit men and people that live in South America, have shown that a high intake of fish and a high omega-3 status is
linked to a lower incidence of many cancers including prostate cancer.
In a 2010 meta-analysis published in the American
Journal of Clinical Nutrition by Szymanski et al, the
authors pooled data from four studies on fish consumption and death from
prostate cancer and found a 63% decrease in risk for high fish consumption.
One must be
very careful with making decisions based on the latest headlines. People do
have a tendency to make decisions based on the last study or news advertised,
rather than the sum of evidence of many studies published on a specific topic.
But we must not do this. We must take into consideration the totality of
evidence that we have on a topic, not just the latest headline on CNN.
In addition,
studies should be read critically – there are inherent flaws in most of them.
The findings
from this most recently reported study: Brasky et al. 2013 ( SELECT) are from
an observational study (looking back in time) and observational studies do not
prove cause and effect.
Scientific studies
that are prospective in design are considered more important in weighing total
evidence and give us more useful guidance in our choices on diet or supplements
that might improve our health.
Are there more useful, prospective studies
that demonstrate protective benefits of omega 3 fatty acids against prostate
cancer?
Yes there
are quite a few. Lets consider some of those.
Researchers
investigated the effect of dietary fish intake amongst 6272 Swedish men who
were followed-up for 30 years. That study reported that men who ate no fish had
a two to three-fold increase in the risk of developing prostate cancer compared
with those who consumed large amounts of fish in their diet.
Another
prospective cohort study based on the Physician’s Health Study found that fish
consumption (≥5 times per week) was not related to prostate cancer risk but was
protective of prostate cancer–specific death.
Other
studies have suggested lower prostate cancer risk with Omega 3 fatty acids from
fish in Swedish men.
And this
study showed lower prostate cancer risk with Omega 3 fatty acids from fish in
Japanese and Brazilian men..
A large
prospective cohort established in 1986 looked at 51,529 American men, 40 – 75
years of age, completed a mailed questionnaire about demographic and medical
information found that a high intake of fish was associated with a lower risk
of metastatic prostate cancer. A similar association was also found for dietary
marine fatty acids from food.
An important
clinical study published by a group at the Harvard School of Public Health
examined the link between dietary fish consumption and the risk of metastatic
prostate cancer. This paper reported results from the Health Professionals
Follow-up Study that involved 47,882 men over twelve years. During the twelve
years, 2,483 cases of prostate cancer were identified. Of these, 617 were
advanced and 278 were metastatic. Eating fish more than three times a week
reduced the risk of prostate cancer but had an even greater impact on the risk
of metastatic prostate cancer. For each additional 500 mg of marine omega-3 consumed,
the risk of metastatic disease decreased by 24%!
And again,
in the 2010 meta-analysis (an analysis of multiple studies) Szymanski and his
team found that a significant 63% reduction in prostate cancer-specific
mortality in those that consumed fish but no link between eating lots of fish
and men’s risk of developing prostate cancer.
When one
considers the larger picture, the headlines claiming that men who consume
omega-3 supplements are at increased risk of prostate cancer, based on one
study where no one used omega-3 supplements, and where levels of omega-3s were
only 0.02% in variance among cancer cases and healthy cases, seem preposterous.
