Just a Little Overweight, But...

Summarized by Robert W. Griffith, MD
September 25, 2006

Summary

Even being a little overweight is associated with an increased risk of death, according to two new studies.

Introduction

There are arguments about the relative importance of weight, body mass index (BMI) and waist-to-hip ratio as the best predictive measure of risk of an early death. Whichever method is used, studies practically all conclude that measurements indicating obesity are linked to increased mortality. However, there is not much evidence concerning people who are 'just a little overweight'. This has been redressed by two studies published in the New England Journal of Medicine. One is from the USA, which we summarize here, and one from Korea¹.

What was done

This study employed data from men and women between 50 and 71. The subjects were enrolled in 1995 - 1996 in the National Institutes of Health (NIH)-AARP Diet and Health Study, when over 560,000 questionnaires were sent out asking for information on a number of items, including dietary intake and health-related behavior. After exclusion of those with inadequate or incomplete information, there were over 525,000 persons included in the analysis.

In the following years the participants' status was checked against the Social Security Administration Death Master File to see if they were still alive or dead. The most recent update was in January 2006.

Height and weight were used to calculate the BMI. (The BMI is defined as the weight in kilograms divided by the square of the height in meters.) Age, gender, race, education level, smoking status, physical activity, alcohol intake, and pre-existing chronic disease were the main items of interest analyzed.

The subjects were classified into 10 distinct categories based on their BMIs, which included the definitions of underweight (BMI less than 18.5), normal weight (BMI 18.5 to 24.9), overweight (BMI 25 to 29.9), and obese (BMI 30 or more).

Analyses were done to calculate the relative risk (RR) of dying according to BMI, adjusted for age, race, education, smoking status, physical activity, and alcohol use. Further analyses addressed bias introduced by pre-existing chronic diseases and smoking status.

What was found

During the follow-up period, which reached 10 years for some participants, 61,000 subjects died (42,000 men and 19,000 women). In both genders, all ethnic groups, and at all ages, death rates were higher in the highest and lowest BMI categories.

When the analysis was limited to healthy people who had never smoked, the risk of death was increased for both the overweight (BMI 25 to 29.9) and the obese, for both men and women. In an analysis confined to 50-55 year-olds, healthy men and women who had never smoked and were overweight had a 30% to 40% increased risk of death, compared to the "normal" category, which had subjects with BMIs of 23.5 to 24.9. Those who were obese had 2 to 3 times the risk versus those in the normal category.

The association between obesity and death was stronger among those without chronic disease than in those with such diseases (emphysema, stroke, kidney disease, or cancer). This emphasized the importance of studying overweight "healthy" subjects when looking for any increased mortality risk.

The risk of death was increased by 50% in those who were underweight (BMI below 18.5), illustrating the "J-shaped curve" nature of the relationship between weight and mortality.

What these results mean

This study confirmed the increased risk of death in people with obesity in both men and women in all racial groups and at all ages. After adjusting the data to allow for the effects of smoking and/or chronic illness, there was also an increased risk of death in those with only moderate increases in BMI. Healthy non-smoking participants who were overweight at age 50 were 20% to 40% more likely to die prematurely than those with a normal BMI.

These results are supported by those from the Korean study published in the same journal¹. Taken together, the findings show that adiposity is a worldwide problem, with only a small degree of overweight representing an increased risk of death. Fortunately, even small reductions in individual baby boomer's weight can improve their chances of reaching a more normal BMI and a more normal life span.

Source

• Overweight, obesity, and mortality in a large prospective cohort of persons 50 to 71 years old. KF. Adams, A. Schatzkin, TB. Harris,  et al., N Engl J Med, 2006, vol. 355, pp. 763--778

Footnotes
1. Jee SH, Sull JW, Park J, et al. Body-mass index and mortality in Korean men and women. New Engl J Med 2006;355:779-787

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