The Impact of Lifestyle Factors on Incidence of Diabetes Later in Life

The combined impact of lifestyle factors on incidence of diabetes mellitus later in life has not been well established. The objective of this study was to determine how lifestyle factors, assessed in combination, relate to new-onset diabetes in a broad and relatively unselected population of older adults.

We prospectively examined associations of lifestyle factors, measured using repeated assessments later in life, with incident diabetes mellitus during a 10-year period (1989-1998) among 4,883 men and women 65 years or older (mean [SD] age at baseline, 73 [6] years) enrolled in the Cardiovascular Health Study. Low-risk lifestyle groups were defined by physical activity level (leisure-time activity and walking pace) above the median; dietary score (higher fiber intake and polyunsaturated to saturated fat ratio, lower trans-fat intake and lower mean glycemic index) in the top 2 quintiles; never smoked or former smoker more than 20 years ago or for fewer than 5 pack-years; alcohol use (predominantly light or moderate); body mass index less than 25 (calculated as weight in kilograms divided by height in meters squared); and waist circumference of 88 cm for women or 92 cm for men. The main outcome measure was incident diabetes defined annually by new use of insulin or oral hypoglycemic medications. We also evaluated fasting and 2-hour postchallenge glucose levels.

The results showed that, during 34,539 person-years, 337 new cases of drug-treated diabetes mellitus occurred (9.8 per 1000 person-years). After adjustment for age, sex, race, educational level, and annual income, each lifestyle factor was independently associated with incident diabetes. Overall, the rate of incident diabetes was 35% lower (relative risk, 0.65; 95% confidence interval, 0.59-0.71) for each 1 additional lifestyle factor in the low-risk group. Participants whose physical activity level and dietary, smoking, and alcohol habits were all in the low-risk group had an 82% lower incidence of diabetes (relative risk, 0.18; 95% confidence interval, 0.06-0.56) compared with all other participants. When absence of adiposity (either body mass index <25 or waist circumference < or =88/92 cm for women/men) was added to the other 4 low-risk lifestyle factors, incidence of diabetes was 89% lower (relative risk, 0.11; 95% confidence interval, 0.01-0.76). Overall, 9 of 10 new cases of diabetes appeared to be attributable to these 5 lifestyle factors. Associations were slightly attenuated, but still highly significant, for incident diabetes defined by medication use or glucose level.

From the results of the study it was concluded that, even later in life, combined lifestyle factors are associated with a markedly lower incidence of new-onset diabetes mellitus.

Diabetes prevention trials have demonstrated the benefits of lifestyle modification for preventing or delaying diabetes onset in high-risk subjects. Although not a direct test of modification, the current study shows that lifestyle factors are nonetheless strongly associated with new-onset diabetes among the elderly. Indeed, the finding that about 90% of new diabetes cases may be due to lifestyle factors is remarkable. To date, prediction of diabetes has often focused on biological parameters. For example, data from the Framingham Offspring study indicated that a risk score using age, sex, parental history of diabetes, and simple clinical variables (fasting glucose, BMI, HDL cholesterol, and triglycerides) could produce an area under the curve of 0.88. In the current study, it would have been nice to see an analysis that included lab values to determine whether lifestyle factors were independent of known predictors of diabetes. However, the investigators chose not to include such factors, arguing that they could be mediators in the causal pathway for effects of lifestyle on diabetes risk. If so, the lifestyle factors may have provided little explanatory power, but that would be because measures such as fasting glucose and dyslipidemia may represent a history of poor lifestyle choices. Among the elderly, those currently practicing low-risk lifestyles likely have been doing so for much of their lives. Thus, one could easily argue that the laboratory measures are actually proxies for lifestyle factors. In any case, this study suggests that there are enormous benefits to low-risk lifestyles that extend well into advanced age.

PreMedline Identifier: 19398692; From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. Arch Intern Med. 2009;169:798-807