Friday, January 14, 2005
By Steven Milloy
Eating a hamburger a day can increase your risk of colon cancer (search),
according to a new study. Is it time to switch to chicken, fish or tofu ? Or
is time to ask your congressman to check into whether the National Cancer
Institute is spending its budget wisely?
Researchers from the National Cancer Institute and the American Cancer
Society concluded in this week’s Journal of the American Medical Association
(Jan. 12) that “prolonged high consumption of red and processed meat may
increase the risk of cancer in the distal portion of the large intestine.”
Their “conclusion” is based on a study of 148,610 adults aged 50 to 74 years
who provided information on meat consumption in 1982 and again in 1992/1993
as part of their enrollment in the Cancer Prevention Study II (search).
Through Aug. 31, 2001, a total of 1,667 cases of colorectal cancers were
reported among the study subjects.
I suspect that the researchers actually had no conclusion worth reporting
after they did an initial analysis of their data. They reported, in fact, no
association between red meat consumption and overall colon cancer risk after
considering the study subjects’ exposures to other colon cancer risk
factors.
They parsed the results as follows, “High intake of red meat reported in
1992/1993 was associated with higher risk of colon cancer after adjusting
for age and energy intake but not after further adjustment for body mass
index, cigarette smoking and other [risk factors],” they stated in the
study. Facing the prospect of no result, I think the researchers then
engaged in some slicing-and-dicing of their data in hopes of discovering
some statistical correlation they could point to as a “risk.”
Since there was no correlation between red meat consumption and overall
cancer risk, the researchers examined their data looking to see whether
there was an association between red meat consumption and cancer of the
proximal colon (search), distal colon (search) and of the rectosigmoid
(search) and rectum. The more analyses performed, after all, the greater the
likelihood that some newsworthy result will be found, albeit, due to chance
perhaps.
These subsequent analyses produced three correlations on which the scary
headlines are based: a 50 percent increase in distal cancer risk among high
consumers of processed meats; a 53 percent increase in distal cancer risk
among those with the highest ratio of meat to chicken and fish consumption;
and a 71 percent increase in rectal cancer risk among high consumers of red
meat.
With respect to the claims concerning distal cancer risk, both results are
of unimpressive size — risks smaller than 100 percent don’t have much
credibility. They are of borderline statistical significance — meaning that
there is a good possibility that the results are due to chance. This
statistical weakness is in large part due to the fact that they are based on
analyses involving only 79 and 92 cases of distal cancer, respectively. For
these analyses to start to be taken seriously, they should involve hundreds,
not dozens, of cancer cases.
As to the reported 71 percent increase in rectal cancer risk among red meat
eaters, I can only conclude that this result was cherry-picked for
sensationalistic purposes. The 71-percent claim is based on an analysis
involving only the 1992/1993 data. When the analysis includes the 1982 data,
the result drops to 43 percent and becomes statistically insignificant.
These weak statistics are just the surface of the problem. Likely nullifying
the entire study is the unreliability of the researchers’ data.
The data for the study was initially collected by 77,000 untrained
volunteers who interviewed family and friends about their lifestyle habits.
None of this lifestyle data was verified or validated.
Exactly what and how much the study subjects ate, smoked, drank, and how
much they exercised is really anybody’s guess. And forget about reliable
information on genetic predisposition to colon cancer, which is thought to
be a major risk factor. The researchers acknowledged in their write-up that
they didn’t even have any information on family history of colon cancer for
the analysis of 1992/1993 data.
The results of previous studies on meat consumption and colon cancer have
produced similar inconsistent, contradictory, weak and even nonsensical
results. There really is no persuasive evidence that meat consumption is in
any way related to colon cancer risk.
So what’s up with this study?
Aside from the usual hijinks of researchers looking for media attention and
their next grant, I noticed that one of this study’s authors has somewhat of
a track record trying to link meat consumption with cancer.
The National Cancer Institute’s Rashmi Sinha (search) has a long history of
trying to use weak statistics to convict meat of causing cancer. I first
brought her antics to the attention of my FoxNews.com readers in a November
2000 column amid her crusade to link well-done meat with cancer.
It appears that Dr. Sinha remains bent on using her position at the National
Cancer Institute to scare us away from eating meat. She’s been at it since
at least 1994, but with little to show except a stack of scary, but
unsupported headlines — which in itself is somewhat revealing.
If after all the time and effort Sinha has put into trying to link meat
consumption with cancer, she still can’t do it, isn’t it time that the NCI
reassign her to more productive work?
Steven Milloy publishes JunkScience.com and CSRwatch.com, is adjunct scholar
at the Cato Institute, and is the author of Junk Science Judo: Self-defense
Against Health Scares and Scams (Cato Institute, 2001).
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