While studies have linked being either underweight or
overweight to poor health, the effect of being overweight
or obese on the risk of dying has been a topic of recent
controversy. Researchers have long used the body-mass index
— weight in kilograms divided by the square of height
in meters — as a measure of the appropriateness of
weight in relation to height.
Researchers from Yonsei University, in Seoul, South
Korea, and the Johns Hopkins Bloomberg School of Public
Health report in one of the largest studies to date
that having either a high or low body-mass index increases
risk of death. The researchers found that the effect of BMI
on the risk of dying varied among major causes of death and
that the risk of death from being overweight or obese was
greater in younger people. The study is published in the
Aug. 24 edition of The New England Journal of
Medicine.
"The relationship between being underweight or
overweight and the risk of death is controversial because,
of the few studies on this topic, most were not able to
pinpoint at what BMI the risk of death increased. The
results from these other studies were also mixed; some of
them did not show an increase in risk of death," said Sun
Ha Jee, lead author of the study and an associate professor
of epidemiology at Yonsei University.
The authors examined the effect of body weight on the
risk of death of more than 1.2 million 30- to 95-year-old
Koreans over a 12-year time span. They looked at death from
any cause and also from specific diseases, such as cancer,
atherosclerotic cardiovascular disease and respiratory
disease. The study participants, who were part of the
Korean Cancer Prevention Study, had an average BMI of 23.2,
regardless of sex; the majority of participants had a BMI
below 25, which is considered a normal weight. By
comparison, the average BMI in the United States is
currently 27.8 for men 20 years and older and 28.1 for
women 20 years and older. Compared to normal-weight
Koreans, underweight, overweight and obese men and women
had higher rates of death. Men and women who had never
smoked and had a BMI of 23.0 to 24.9 had the lowest risk of
death from any cause.
The researchers found that the relationship of BMI to
risk of dying varied among the major causes of death
considered. The risk of death from cancer increased
beginning at BMI levels of 26.0 to 28.0 and rose at higher
levels. Risk for death from respiratory causes was highest
at the lowest BMI values and decreased with higher BMI
values, whereas the risk of death from atherosclerotic
cardiovascular disease increased progressively with higher
BMI values. Information on cardiovascular risk factors
showed an increasingly unfavorable profile with increasing
BMI values. Study participants younger than 50 years of age
had the highest relative risk of death associated with a
high BMI. The researchers report no evidence of an
increased risk of death for obese individuals 65 years of
age and older.
Jonathan M. Samet, senior author of the study and
professor and chair of the Bloomberg School's
Department of Epidemiology, said, "Past studies were
conducted primarily in Western populations, and we did not
know if these results would apply in Asian populations,
which tend to be thinner but have a higher percentage of
body fat than do their Western counterparts."
The number of respiratory causes of death, such as
tuberculosis, pneumonia, chronic obstructive pulmonary
disease and asthma, differ between Koreans and inhabitants
of Western countries.
Jee, who is also an adjunct associate professor at the
Bloomberg School, noted that the study results cannot be
generalized to other populations.
The study was supported by grants from the National
Cancer Institute, National Institutes of Health, Department
of Health and Human Services and Korean Seoul City Research
and Development program.
In addition to Jee and Samet, the study is co-authored
by Eliseo Guallar and Jae Woong Sull, both of the Bloomberg
School of Public Health; Jungyong Park and Heechoul Ohrr,
Yonsei University; and Sang-Yi Lee, Cheju National
University and National Health Insurance Corporation,
Korea.
GO TO