Cause-Specific Excess Deaths Associated With Underweight, Overweight, and Obesity
- From: MarilynMann <mannm@xxxxxxxxxxx>
- Date: Tue, 06 Nov 2007 16:53:23 -0800
Cause-Specific Excess Deaths Associated With Underweight, Overweight,
and Obesity
Katherine M. Flegal, PhD; Barry I. Graubard, PhD; David F. Williamson,
PhD; Mitchell H. Gail, MD, PhD
JAMA. 2007;298(17):2028-2037.
Context The association of body mass index (BMI) with cause-specific
mortality has not been reported for the US population.
Objective To estimate cause-specific excess deaths associated with
underweight (BMI <18.5), overweight (BMI 25-<30), and obesity (BMI
30).
Design, Setting, and Participants Cause-specific relative risks of
mortality from the National Health and Nutrition Examination Survey
(NHANES) I, 1971-1975; II, 1976-1980; and III, 1988-1994, with
mortality follow-up through 2000 (571 042 person-years of follow-up)
were combined with data on BMI and other covariates from NHANES
1999-2002 with underlying cause of death information for 2.3 million
adults 25 years and older from 2004 vital statistics data for the
United States.
Main Outcome Measures Cause-specific excess deaths in 2004 by BMI
levels for categories of cardiovascular disease (CVD), cancer, and all
other causes (noncancer, non-CVD causes).
Results Based on total follow-up, underweight was associated with
significantly increased mortality from noncancer, non-CVD causes (23
455 excess deaths; 95% confidence interval [CI], 11 848 to 35 061) but
not associated with cancer or CVD mortality. Overweight was associated
with significantly decreased mortality from noncancer, non-CVD causes
(-69 299 excess deaths; 95% CI, -100 702 to -37 897) but not
associated with cancer or CVD mortality. Obesity was associated with
significantly increased CVD mortality (112 159 excess deaths; 95% CI,
87 842 to 136 476) but not associated with cancer mortality or with
noncancer, non-CVD mortality. In further analyses, overweight and
obesity combined were associated with increased mortality from
diabetes and kidney disease (61 248 excess deaths; 95% CI, 49 685 to
72 811) and decreased mortality from other noncancer, non-CVD causes (-
105 572 excess deaths; 95% CI, -161 816 to -49 328). Obesity was
associated with increased mortality from cancers considered obesity-
related (13 839 excess deaths; 95% CI, 1920 to 25 758) but not
associated with mortality from other cancers. Comparisons across
surveys suggested a decrease in the association of obesity with CVD
mortality over time.
Conclusions The BMI-mortality association varies by cause of death.
These results help to clarify the associations of BMI with all-cause
mortality.
Author Affiliations: National Center for Health Statistics, Centers
for Disease Control and Prevention, Hyattsville (Dr Flegal) and
Division of Cancer Epidemiology and Genetics, National Cancer
Institute, Bethesda (Drs Graubard and Gail), Maryland; and Division of
Diabetes Translation, Centers for Disease Control and Prevention,
Atlanta, Georgia (Dr Williamson).
* * *
By GINA KOLATA
Published: November 7, 2007
About two years ago, a group of federal researchers reported that
overweight people have a lower death rate than people who are normal
weight, underweight or obese. Now, investigating further, they found
out which diseases are more likely to lead to death in each weight
group.
For the first time linking causes of death to specific weights, they
report that overweight people have a lower death rate because they are
much less likely to die from a grab bag of diseases that includes
Alzheimer's and Parkinson's, infections and lung disease. And that
lower risk is not counteracted by increased risks of dying from any
other disease, including cancer, diabetes or heart disease.
As a consequence, the group from the Centers for Disease Control and
Prevention and the National Cancer Institute reports, there were more
than 100,000 fewer deaths among the overweight in 2004, the most
recent year for which data were available, than would have been
expected if those people had been of normal weight.
Their paper is being published in The Journal of the American Medical
Association.
The researchers also confirmed that obese people and people whose
weights are below normal have higher death rates than people of normal
weight. But, when they asked why, they found that the reasons were
different for the different weight categories.
Some who studied the relation between weight and health said the
nation might want to reconsider what are ideal weights.
"If we use the criteria of mortality, then the term 'overweight' is a
misnomer," said Daniel McGee, professor of statistics at Florida State
University.
Others said there were plenty of reasons that being overweight was not
desirable.
"Health extends far beyond mortality rates," said Dr. JoAnn Manson,
chief of preventive medicine at Brigham and Women's Hospital in
Boston.
Dr. Manson added that other studies, including ones at Harvard, found
that being obese or overweight increased a person's risk for any of a
number of diseases, including diabetes, heart disease and several
forms of cancer. And, she added, excess weight makes it more difficult
to move about and impairs the quality of life.
"That's the big picture in terms of health outcomes," Dr. Manson said.
"That's what the public needs to look at."
Researchers generally divide weight into four categories - normal,
underweight, overweight and obese - based on the body mass index,
which is a measure of body fat based on height and weight. A woman who
is 5-foot-4, for instance, would be considered at normal weight at
130, underweight at 107 pounds, overweight at 150 pounds and obese at
180.
In this study, those with normal weight were considered the baseline
and others were compared to them.
The researchers, led by Katherine Flegal, of the Centers for Disease
Control and Prevention, said the big picture they found was
surprisingly complex. The higher death rate in obese people, as might
be expected, was almost entirely driven by a higher death rate from
heart disease.
But, contrary to expectations, the obese did not have an increased
risk of dying from cancer. They were slightly more likely than people
of normal weights to die of a handful of cancers that are thought to
be related to excess weight - cancers of the colon, breast, esophagus,
uterus, ovary, kidney and pancreas. Yet they had a lower risk of dying
from other cancers, including lung cancer. In the end, the increases
and decreases in cancer risks balanced out.
As for diabetes, it showed up in the death rates only when the
researchers grouped diabetes and kidney disease as one category.
Diabetes can cause kidney disease, they note. But, the researchers
point out, the number of diabetes deaths may be too low because many
people with diabetes die from heart disease, and often the cause of
death is listed as a heart attack.
The diverse collection of diseases other than cancer, heart disease
and diabetes, which show up in the analyses of the underweight and the
overweight, have gone relatively unscrutinized among epidemiologists,
noted Dr. Mitchell Gail, a cancer institute scientist and an author of
the paper. But, Dr. Gail added, "these are not a negligible source of
mortality."
The new study began several years ago when the investigators used
national data to look at death risks according to body weight. They
concluded that, compared with people of normal weight, the overweight
had a decreased death risk and the underweight and obese had increased
risk.
That led them to ask: If being fat or thin affects a person's life
span, what diseases, exactly, are those individuals at risk for, or
protected from?
The research involved analyzing data from three large national
surveys, the National Health and Nutrition surveys, which are
administered by the National Center for Health Statistics. Their
participants are a nationally representative group of Americans who
are weighed and measured, assuring that heights and weights are
accurate, and followed until death. The investigators determined the
causes of death by asking what was recorded on death certificates.
The researchers caution that a study like theirs cannot speak to cause
and effect. They do not yet know, precisely, what it is about being
underweight, for instance, that increases the death rate from
everything except heart disease and cancer. Researchers tried to rule
out those who were thin because they might have been already sick. And
they also ruled out smokers, and the results did not change.
Dr. Gail, though, had some advice, which, he said, is his personal
opinion as a physician and researcher: "If you are in the pink and
feeling well and getting a good amount of exercise and if your doctor
is very happy with your lab values and other test results, then I am
not sure there is any urgency to change your weight."
.
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