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The newspaper of The Johns Hopkins University September 5, 2006 | Vol. 36 No. 1
Low or High Body-Mass Index Increases Risk of Death

By Kenna Lowe
School of Public Health

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.


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