While studies have linked being either underweight oroverweight to poor health, the effect of being overweightor obese on the risk of dying has been a topic of recentcontroversy. Researchers have long used the body-mass index— weight in kilograms divided by the square of heightin meters — as a measure of the appropriateness ofweight in relation to height.

Researchers from Yonsei University, in Seoul, SouthKorea, and the Johns Hopkins Bloomberg School of PublicHealth report in one of the largest studies to datethat having either a high or low body-mass index increasesrisk of death. The researchers found that the effect of BMIon the risk of dying varied among major causes of death andthat the risk of death from being overweight or obese wasgreater in younger people. The study is published in theAug. 24 edition of The New England Journal ofMedicine.

"The relationship between being underweight oroverweight and the risk of death is controversial because,of the few studies on this topic, most were not able topinpoint at what BMI the risk of death increased. Theresults from these other studies were also mixed; some ofthem did not show an increase in risk of death," said SunHa Jee, lead author of the study and an associate professorof epidemiology at Yonsei University.

The authors examined the effect of body weight on therisk of death of more than 1.2 million 30- to 95-year-oldKoreans over a 12-year time span. They looked at death fromany cause and also from specific diseases, such as cancer,atherosclerotic cardiovascular disease and respiratorydisease. The study participants, who were part of theKorean Cancer Prevention Study, had an average BMI of 23.2,regardless of sex; the majority of participants had a BMIbelow 25, which is considered a normal weight. Bycomparison, the average BMI in the United States iscurrently 27.8 for men 20 years and older and 28.1 forwomen 20 years and older. Compared to normal-weightKoreans, underweight, overweight and obese men and womenhad higher rates of death. Men and women who had neversmoked and had a BMI of 23.0 to 24.9 had the lowest risk ofdeath from any cause.

The researchers found that the relationship of BMI torisk of dying varied among the major causes of deathconsidered. The risk of death from cancer increasedbeginning at BMI levels of 26.0 to 28.0 and rose at higherlevels. Risk for death from respiratory causes was highestat the lowest BMI values and decreased with higher BMIvalues, whereas the risk of death from atheroscleroticcardiovascular disease increased progressively with higherBMI values. Information on cardiovascular risk factorsshowed an increasingly unfavorable profile with increasingBMI values. Study participants younger than 50 years of agehad the highest relative risk of death associated with ahigh BMI. The researchers report no evidence of anincreased risk of death for obese individuals 65 years ofage and older.

Jonathan M. Samet, senior author of the study andprofessor and chair of the Bloomberg School's Department of Epidemiology , said, "Past studies wereconducted primarily in Western populations, and we did notknow if these results would apply in Asian populations,which tend to be thinner but have a higher percentage ofbody fat than do their Western counterparts."

The number of respiratory causes of death, such astuberculosis, pneumonia, chronic obstructive pulmonarydisease and asthma, differ between Koreans and inhabitantsof Western countries.

The study was supported by grants from the NationalCancer Institute, National Institutes of Health, Departmentof Health and Human Services and Korean Seoul City Researchand Development program.

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