Linda B. Bobroff, Ph.D., RD, LD/N
Professor and Extension Nutrition Specialist
The number of people who are either overweight or obese is on the rise in the U.S. and many other countries. It is fairly well accepted that being obese can increase risk of death; however, it is not clear from the literature if being overweight (as opposed to obese) imparts a similar risk. Two recent papers examine this issue among older persons in the U.S. and Korea.
Background
Weight status often is defined as a ratio of body weight in kilograms to height in meters squared – the body-mass index or BMI. For adults, a BMI from 18.5 to 24.9 is defined as normal or healthy, 25.0 to 29.9 as overweight, and 30.0 or more as obesity (Adams 2006). In the U.S. during the last two decades the percent of adults who are overweight or obese has increased significantly. Approximately one-third of adults currently are classified as obese putting them at increased risk for diabetes, cardiovascular disease, and some cancers, and increasing their risk of premature death (USDHHS 2005).
Lifestyle practices often associated with obesity, including poor diet and physical inactivity, are second only to smoking as a leading cause of death, causing an estimated 400,000 deaths (16.6% of deaths) in 2000. These statistics, along with rising health care costs and an aging population, have stimulated significant interest in prevention and management of overweight and obesity (Mokdad 2004). The following studies examine the question of whether or not being overweight increases risk of death among adults in the U.S. and Korea.
U.S. Study (Adams 2006)
Researchers examined BMI in relation to the risk of death from any cause in a cohort of 527,265 men (313,047) and women (214,218) in six states in the U.S. who were 50 to 71 years old at their enrollment in the 10-year study. The researchers calculated BMIs from self-reported heights and weights, submitted via a mailed questionnaire. They calculated both current BMI, as well as BMI at age 50 based on recalled weight reported in a supplementary questionnaire mailed six months after the initial contact.
During the 10-year study, 61,317 participants died (42,173 men and 19,144 women). As expected, those in the lowest or highest categories of BMI (<18.5 and $40.0) had an increased risk of death. This was observed in men and women, all racial or ethnic groups, and at all ages at time of enrollment in the study. Among men, those in the BMI category <18.5 had a relative risk of death of 1.97 and those with a BMI $40.0 had a relative risk of death of 1.83. In other words, these men were approximately two times more likely to die than men in the healthy BMI range of 23.5-24.9 which was the reference group (relative risk = 1.00). In women, those in the BMI category <18.5 had a relative risk of death of 2.03 and those with a BMI $40.0 had a relative risk of death of 1.94, similar to the outcomes among men. These data constitute a U-shaped relation between BMI and risk of death, with the lowest risk in the middle BMI categories. With increasing age, the elevated risks at the two extremes of BMI declined slightly. These results support earlier studies that show increased risk of death in both underweight and obese persons.
When the researchers restricted their analysis to persons who were healthy and had never smoked, they found an increased risk of death in overweight as well as obese men and women. The associations were even stronger when they examined BMI in midlife (50 years of age) among those who had never smoked. In this cohort, the risk of death increased by 20 to 40 percent in overweight persons, and by two to three times among those who were obese.
Korean Study (Jee 2006)
This study also examined the association between BMI and risk of death. The subjects were 1,213,829 Korean men (770,556) and women (443,273) between 30 and 95 years of age, a wider age range. BMIs were calculated using height and weight measurements taken at physical examinations at local hospitals. The average BMI was 23.2.
In the 12 years of follow-up, 82,372 people died, including 58,312 men and 24,060 women. The lowest death rates were in men and women with BMI 23.0 to 24.9. As in the previous study, those at the lowest and highest BMI ranges had the highest death rates, although the differences were not as large in this study. In men, those in the BMI category <18.5 had a hazard ratio (basically the same statistic as the relative risk of the previous study) of 1.29 and those with a BMI $30.0 had a hazard ratio of 1.71. The reference in this study also was the BMI range of 23.0-24.9, with a hazard ratio of 1.0. In women, those in the BMI category <18.5 had a hazard ratio of 1.17 and those with a BMI $30.0 had a hazard ratio of 1.20. These are smaller difference than those observed in the U.S. study. There was little evidence of an effect of BMI on death risk among persons over 65 years of age.
Slightly higher death rates in persons with low BMIs in this population may be due to a relatively high incidence of respiratory diseases such as chronic obstructive pulmonary disease (COPD) and pneumonia in Korea, both of which are associated with severe weight loss. These researchers examined risk of death from specific causes. Risk of death from atherosclerotic cardiovascular disease increased with increasing BMI in men (hazard ratio 1.94 in men with BMI $32.0). Risk of death from cancer increased slightly among overweight persons and more significantly among those with a BMI over 30.
Overall, the BMIs of this cohort were lower than those of the U.S. cohort. However, the authors note that Asian populations tend to have higher percent body fat than do Western populations at a given BMI, placing them at higher risk for diseases at lower BMIs. Due to this difference, the World Health Organization has recommended that cutoff points for overweight and obesity should be lower for Asian populations (WHO 2000).
Implications for Extension
There is a substantial body of evidence that obese persons are at increased risk of disease and early death, although some health professionals disagree with this conclusion. The U.S. study reported here indicates that persons who are overweight also may be at risk of early death, although this likely will continue to be debated in the literature and the focus of future research. Both studies indicate that risk of death among older persons may be less affected by BMI, although this too may need further research.
As Extension professionals, we can make positive impacts in the lives of persons who are either overweight or obese by offering healthy lifestyle programs that focus on behaviors over which they have control (e.g., eating and exercise behaviors), and that promote health and physical fitness, regardless of body weight. Weight management programs may have their most positive impacts on persons in midlife who are obese since they are at high risk for chronic diseases and early death, and there is evidence that even small changes in body weight can greatly reduce risk of disease, such as diabetes (Knowler 2002). Still, our primary focus should be on positive lifestyle changes rather than weight loss, and on improved health parameters such as blood glucose, blood pressure, and blood lipids, since they indicate risk for the major disease that kill Americans.
The 11-session Toward Permanent Weight Management (TPWM) program recently was updated and is available for your use (CD will be available soon). TPWM focuses on healthful eating, physical activity, behavior modification, and size acceptance. Another weight management program, the University of Florida Women’s Weight Loss Research Program is part of an NIH-funded project that included the six-month weight loss intervention, followed by a 12-month maintenance program in three different formats (the research component). This study is being completed in six county Extension offices in north central Florida, and the team (Bobroff is one of the co-investigators) has applied for additional funding to test various program lengths and make it more adaptable for Extension.
References
Adams KF, Schatzkin A, Harris T, Kipnis V, Mouw T, Ballard-Barbash R, Hollenbeck A and Leitzmann MF. Overweight, obesity, and mortality in a large prospective cohort of persons 50 to 71 years old. New Engl J Med. 2006;355:763-778.
Jee SH, Sull JW, Park J, Lee S0Y, Ohrr H, Guallar E and Samet JM. Body-mass index and mortality in Korean men and women. New Engl J Med. 2006;355:779-787.
Knowler WC, Barrett-Connor E, Fowler SE, et al. Reduction in the incidence of type 2 diabetes with lifestyle intervention or metformin. N Engl J Med. 2002;346:393-403.
Mokdad AH, Marks JS, Stroup DF and Gerberding JL. Actual causes of death in the United States, 2000. JAMA 2004;291:1238-1245.
U.S. Department of Health and Human Services and U.S. Department of Agriculture. Dietary Guidelines for Americans, 2005. 6th Edition, Washington, DC: U.S. Government Printing Office, January 2005. Available at: www.healthierus.gov/dietaryguidelines. Accessed: September 28, 2006.
