By Steven Milloy
Obesity is associated with a variety of health problems. However, there
are conflicting results and genuine controversy over whether just being
moderately overweight is a health risk.
This study by Kenchaiah et al. in the New England Journal of
Medicine (Aug. 1, 2002) doesn’t resolve this
controversy, despite the claims of the researchers and the accompanying
editorial.
Taken in the best light, the results are statistically weak. Even so,
the reported results for men and women inexplicably conflict.
Finally, there was no medical determination that overweight caused the
observed cases of heart failure - not in one case. The researchers attempted to make
the link with statistics alone. Family history of heart problems and physical
activity were not considered as confounding risk factors for heart failure.
The researchers used statistical trickery and outright dishonesty to
make their claims.
The bottom line is that this study does not link
overweight with heart failure.
The study authors acknowledge at the outset of their article that the studies to date linking overweight with obesity are inconclusive:
Whereas extreme obesity has been associated with
heart failure, data are limited regarding the influence of overweight and
lesser degrees of obesity on the risk of heart failure.
The researchers grouped their study subjects by body mass index (BMI)
into three categories: Normal (BMIs 18.5-24.9); Overweight (BMIs 25.0-29.9);
and Obese (BMIs greater than 30.0).
Confounding risk factors for heart failure were considered in two ways:
(1) base line - defined at the beginning of the study; and (2) time dependent - updated every four
years.
For these groupings, the authors report weak statistical associations
among overweight women and heart disease for base line and time dependent
confounding factors: - (1) Base line confounders, Relative Risk = 1.50, 95% Confidence
Interval (1.12 – 2.02); (2) Time dependent confounders, Relative Risk = 1.68,
95% Confidence Interval (1.25- 2.27).
These results are too weak to be meaningful. As the National Cancer Institute
states,
"In epidemiologic research, relative risks of
less than 2.0 are considered small and usually difficult to interpret. Such
increases may be due to chance, statistical bias or effects of confounding
factors that are sometimes not evident."
For men, the reported results are also weak and - worse - not statistically
significant, meaning that they could be flukes: (1) Base line confounders,
Relative Risk = 1.20, 95% Confidence Interval (0.87 – 1.64); and (2) Time
dependent confounders, Relative Risk = 1.17, 95% Confidence Intervals
(0.86-1.61). Because the lower bounds of the confidence intervals are less than
1.0, the relative risks aren’t statistically significant.
These results are problematic for the researchers not only because are
they weak, but because they conflict even if the weakness is ignored. That is,
the result for men isn’t statistically significant and so cannot be viewed as
linking overweight with heart failure. If overweight was a real risk factor for
heart failure, why in women, but not men? They offer no explanation and this
problem is fatal to the link.
So the researchers tried statistical trickery to eliminate this
problem. They looked at BMI as a “continuous variable” - i.e., BMI categories in
increments of 1 such as 25.0-25.9, 26.0-26.9, etc.
But even this failed as the (again) weak associations still conflicted.
For women, the reported association was: Relative Risk = 1.07, 95%
Confidence Interval (1.04 – 1.10). For men, the reported association was: - Relative Risk = 1.04,
95% Confidence Interval (1.00 – 1.07).
The men’s result is again not statistically significant as the
confidence interval includes the no-effect level of 1.0. This result does not
link overweight with heart disease and inexplicably conflicts with the women’s
result.
The authors acknowledge this problem, but ignore it:
Although the hazard ratio for heart failure in
overweight men did not achieve statistical significance, analyses evaluating
body mass index as a continuous variable and findings of trend models support
the existence of a continuous gradient of heart-failure risk with increasing
body mass index in both sexes.
Their statement about the continuous variable supporting an association
between BMI and heart failure is obviously false - the men’s confidence interval includes the value 1.0
and so the relative risk is not statistically significant.
Their claim that “trend models” support the association is also
incorrect.
The trend model relies on the existence of the reported men’s relative
risk which, as discussed above, is not statistically significant. If the
relative risk is not statistically significant, then it cannot be a data point.
So there is no “trend.”
Finally, the accompanying editorial, written by a consultant to drug
manufacturers Bristol-Myers Squibb and Merck, promotes the spurious link
between overweight and heart failure apparently to sell drugs to the population
of overweight people:
On the basis of the findings… overweight and,
particularly obesity should now be added to the list of risk factors for the
development of heart failure…. Certain therapies for hypertension and diabetes,
such as inhibitors of the rennin-angiotensin system and metformin, appear to be
particularly effective for treating or preventing some of the consequences of
overweight and obesity and may thereby reduce the risk of heart failure. Other
therapies, such as antiplatelet drugs for dyslipidemia, may accomplish the same
goal…
Is this yet another embarrassing conflict of interest for the New
England Journal of Medicine?
Steven Milloy is the publisher of
JunkScience.com , an
adjunct scholar at the Cato Institute and the author of Junk Science Judo:
Self-defense Against Health Scares and Scams (Cato Institute, 2001).