Even as science searches for more clues about the causes of diabetes and medications to prevent it, the vast majority of new cases of the disease in older adults could be prevented by following a modestly healthier lifestyle, according to research led by scientists at the Harvard School of Public Health (HSPH).
Researchers have found that a combination of five lifestyle factors could account for nine in 10 new cases of type 2 diabetes in men and women age 65 and older. The lifestyle factors that were examined included physical activity, diet, smoking habits, alcohol use, and amount of body fat (as determined by body mass index and waist circumference).
The findings highlight that diabetes really is a lifestyle disease and is largely preventable, said lead author Dariush Mozaffarian, assistant professor of epidemiology at HSPH and assistant professor of medicine in the Division of Cardiovascular Medicine, Brigham and Women's Hospital and Harvard Medical School. Although previous studies had linked these lifestyle factors separately to diabetes or in sum to risk of diabetes in specific socioeconomic populations, this study quantifies the overall impact of several lifestyle factors associated with diabetes risk in a general population of older men and women.
Type 2 diabetes is the most common form of the disease and occurs when the body fails to properly respond to and produce insulin, resulting in a build-up of sugar in the blood and other biologic abnormalities. Incidence of diabetes has jumped in the past decade and is now estimated to affect 24 million Americans, or nearly eight percent of the population, according to the Centers for Disease Control and Prevention. The disease disproportionately affects older Americans.
In this study, researchers tracked 4,883 men and women age 65 or older over a period of 10 years as part of the Cardiovascular Health Study, a multicenter study sponsored by the National Heart, Lung and Blood Institute to evaluate risk factors for cardiovascular disease in older adults. Data was collected through annual questionnaires and physical exams. Participants were asked about their physical activity level, diet, smoking habits, and alcohol use. Their body mass index and waist circumference were measured. Participants were grouped into a low-risk or high-risk group for each factor.
During the study period, more than 300 subjects were diagnosed with diabetes. After making statistical adjustments for age, sex, race, educational level, and annual income, researchers found that each of the five lifestyle factors they measured was independently associated with the onset of diabetes. Overall, the rate of incident diabetes was 35 percent lower for each one additional lifestyle factor in the low-risk group.
Subjects in the low-risk group for diet consumed slightly better-than-average levels of dietary fiber and polyunsaturated fat and less trans fat and starchy and sugary foods. Other low-risk characteristics included whether participants had never smoked; consumed up to two alcoholic drinks per day (modest alcohol consumption has been shown to be a protective factor against diabetes); and were not overweight (defined by having a body mass index below 25 or a waist circumference of less than 88 cm for women or 92 cm for men).
The study results underscore that people can lower their diabetes risk considerably, even if they are unable to follow a perfect ideal of healthy behavior. Very modest differences in lifestyle can have a tremendous impact on diabetes risk, Mozaffarian said. Even two or three or four of the five factors, in any combination, were associated with substantially lower risk.
For instance, he pointed out that diabetes prevention often focuses on weight loss, something that is difficult for many people to achieve. But this study found that independent of any differences in weight, individuals in the low-risk category for only physical activity level and dietary habits had a 46 percent lower incidence of diabetes. Combining low-risk groups for physical activity level, dietary habits, smoking habits and alcohol use produced an 82 percent lower risk of diabetes, and four in five new cases of diabetes appeared to be attributable to not having these low-risk lifestyle factors. Adding either not being overweight or not having large waist circumference was associated with an 89 percent lower risk of diabetes.
Mozaffarian pointed out that the differences in lifestyle between the low-risk and high-risk categories were not extreme. For instance, because participants were divided only into two groups, anyone who participated in physical activity above the average was included in the lower-risk group for that category. These physical activity levels included walking regularly and engaging in leisure activities.
Mozaffarian said that prior work in the Nurses' Health Study showed similarly large associations between lifestyle risk factors and diabetes risk in married U.S. nurses. The new research includes older adults, both sexes, and is drawn from community-based populations, suggesting that these significant benefits of lifestyle are likely to extend to the general population.
Whereas considerable ongoing research is investigating possible genetic causes of type 2 diabetes and the underlying biology of the disease, Mozaffarian said that this study and other studies emphasize that much is already known about how to prevent the majority of cases. "We are entering a public health emergency in obesity and diabetes," he said. "We know how to prevent nearly all cases of type 2 diabetes. We need real and sustained policy, research, and public health focus on this emergency so that we can fix the clear societal and individual causes of this epidemic."
Other study authors are based at the University of Washington and Northwestern University. The study was supported by grants from the National Heart, Lung and Blood Institute, NIH. One author was supported by an unrestricted educational grant from Amgen, Inc., to the Cardiovascular Health Study Coordinating Center.
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