Activity, Obesity, and Type II Diabetes (2002)

OVERVIEW In the United States and much of the rest of the world, industrialization and medical breakthroughs have helped extend average lifespan and reduce the physical demands placed on individuals during their lifetimes. Unfortunately, extension of the health span, that is, the number of yrs spent living disease free, has not kept pace with gains in longevity. Although cardiovascular disease remains as the number one cause of death in many industrialized nations, improvements in medical care have steadily reduced the risk and severity of suffering cardiovascular events. Of growing concern is the rapid spread of obesity and a sedentary lifestyle. As our waists expand, so too do the risks for diseases like diabetes. Obesity-related diseases are estimated to place a $100 billion dollar annual burden on the U.S. healthcare system and costs associated with treating type II diabetes are similar. Several recent reports have documented the relationship between type II diabetes and modifiable lifestyle factors such as exercise, diet, and obesity. Here we highlight findings from three such papers. Mokdad, A.H., B.A. Bowman, E.S. Ford, F. Vinicor, J.S. Marks, and J.P. Koplan. The continuing epidemics of obesity and diabetes in the United States.JAMA. 286:1195–1200, 2001. This is the most recent in a series of articles from this group of investigators at the Centers for Disease Control that describes the prevalence of obesity and diabetes. In 2000, more than 180,000 adults in the United States were randomly contacted by telephone and asked to provide health and lifestyle information. Self-reported height and weight data were used to calculate body mass index (BMI). Based on similar surveys over the last decade, the prevalence of obesity (BMI ≥ 30 kg·m−2) has risen from 12% in 1991 to 20% in the current yr. Over the same time span, the number of people considered overweight (BMI ≥ 25 kg·m−2) rose from 45 to 56%. Obesity prevalence tended to increase with advancing age. Obesity is probably the most important risk factor for the development of type II diabetes, and therefore it is not surprising that diabetes prevalence also increased with age. Overall, 4.9% of participants reported having diabetes in 1991 and this number grew to 7.3% by 2000. A unique aspect of this report compared to previous editions is that data on physical activity and dietary practice are provided. An alarming finding was that more than half (56%) of people said they engaged in little or no regular physical activity. Many people reported that they were trying to lose or maintain their weight, yet very few were using both diet and exercise to achieve these goals. Other interesting trends can be seen due to categorization of the data by geographical location, age, sex, ethnicity, education level, and socioeconomic status. Comment Large-scale studies of this kind are helpful for defining current health trends. The rapid changes in just the last decade are particularly startling and are cause for concern. Mokdad et al. correctly point out that their estimates are likely to be conservative. Although they did not delineate diabetes into type I, type II, and gestational subtypes, it is known that many cases of type II diabetes are undiagnosed so that the actual prevalence of diabetes is likely to be higher than reported in this study. Actual levels of obesity may also be higher because self-reports of height and weight tend to be biased toward more “favorable” values. Another consideration that is not discussed in the paper is body composition. For large-scale surveys, body composition analysis is clearly not feasible. However, some readers will recognize that a limitation of using BMI to categorize obesity is that changes in relative body fatness, which have important metabolic consequences, can be overlooked. This is particularly true when considering the effects of aging where reductions in lean tissue mass, particularly skeletal muscle, are offset by gains in fat mass. Thus, it is likely that Americans are becoming fatter than even this study suggests. Hu, F.B., J.E. Manson, M.J. Stampfer, G. Colditz, S. Liu, C.G. Solomon, and W.C. Willet. Diet, lifestyle, and the risk of Type 2 diabetes mellitus in women.N. Engl. J. Med.345:790–797, 2001. This report comes from the Harvard Nurses’ Health Study, a project that has been tracking health and lifestyle trends in women since 1976. Biennial questionnaires are used to gather health and lifestyle information. Here they analyze risk factors associated with incidence of type II diabetes in nearly 85,000 women. About 4% of the women in the study were diagnosed with new cases of type II diabetes during the period from 1980 to 1996. A key finding was that women with a BMI > 30 were at least 20 times more likely to become diabetic, making BMI the most important risk factor. Even those people in high-normal and overweight ranges were at increased risk. Exercise, diet, and smoking habits were also associated with diabetes onset. Women categorized as having two or more positive lifestyle traits were at the lowest risk of diabetes, even if they had a family history of the disease. Tuomilehto, J., J. Lindstrom, J.G. Eriksson, T.T. Valle, H. Hamalainen, P. Ilanne-Parikka, S. Keinanen-Kiukaanniemi, M. Laakso, A. Louheranta, M. Rastas, V. Salminen, and M. Uusitupa. Prevention of type 2 diabetes mellitus by changes in lifestyle among subjects with impaired glucose tolerance.N. Engl. J. Med.344:1343–1350, 2001. This Finnish study examined whether the onset of type II diabetes could be prevented by modifying the lifestyles of people already at risk. A multicenter trial format was used to enroll 522 overweight, middle-aged men and women with impaired glucose tolerance. Impaired glucose tolerance was defined as having fasting blood glucose < 140 mg·dL−1, but having levels that remained high (140–200 mg·dL−1) 2 h after ingesting oral glucose. This condition is considered an intermediate step in the progression from normal glucose tolerance to diabetes. Subjects were randomly assigned to an intervention group that was given regular, detailed, individual instruction on diet and exercise to lose weight and become more active. Control subjects were annually provided with diet and exercise information in written and oral form, but personalized instruction and follow-up were not performed. Members of the intervention group were more likely to meet goals for weight reduction, dietary modification, and exercise frequency. Over a 6-yr follow-up, the intervention group also had fewer new cases of diabetes and was more likely to have positive changes in oral glucose tolerance. SUMMARY The authors of the first paper conclude that despite increasing awareness by health-care providers and the public, the epidemics of obesity and diabetes continue to worsen in the United States. The studies by Hu et al. and Tuomilehto et al. both clearly demonstrate that type II diabetes risk can be modified by managing body weight (presumably body fatness), remaining physically active, eating properly, and abstaining from smoking. Unfortunately, the Finnish study supports the conclusion of Mokdad et al., that information about diet and exercise are not sufficient alone to cause behavioral change and reduction of disease risk in a vulnerable population. Rather, the positive health changes that were achieved required an active, assertive program of individualized guidance and supervision. To implement such programs on a large scale within the existing healthcare system would require substantial resources. However, considering the enormous socioeconomic costs currently borne to treat obesity and diabetes-related disease, preventive efforts could be a more effective investment. Several campaigns to elicit positive health-related behavior are already in action. At present, perhaps the most publicly prominent message is aimed at reduction or elimination of smoking. The area in greatest need of improvement, as shown by Mokdad et al., is physical activity. For this reason, renewed efforts are being made by organizations such as the American College of Sports Medicine to encourage all people to exercise regularly. It is critical that these programs achieve success to stem the rising tides of obesity and diabetes.