In this large prospective cohort study of men and women age 50 to 71 years at baseline, individuals with a low-risk lifestyle profile, including not smoking, engaging in regular physical activity, consuming a healthful diet, using alcohol in moderation, and having an optimal body weight, had a dramatically lower risk for incident diabetes than individuals who did not have a low-risk profile. Each 1 additional lifestyle factor in the low-risk group was associated with a 31% and 39% lower risk for diabetes among men and women, respectively. This combined influence of lifestyle, while slightly more strongly associated with a lower risk for diabetes among women, was similarly observed among individuals with and without a family history of diabetes and those with higher and lower levels of overall adiposity.
In general, our results are consistent with the limited published research on the role of multiple lifestyle risk factors in the etiology of diabetes. In a relatively homogeneous cohort of middle-age female health professionals of high socioeconomic status, women with all 5 lifestyle factors in the low-risk group had a relative risk for diabetes of 0.09 (95% CI: 0.05, 0.17) (13
). In another smaller scale study of older adults, each 1 additional lifestyle factor in the low-risk group was associated with a 35% lower risk for diabetes (14
). However, in the study of older adults, limited power was available to compare risks between the sexes as well as across other potentially important modifiable factors. Large prospective studies such as ours are especially valuable for determining a precise dose response gradient for the connection between lifestyle and diabetes. Our large cohort also enabled us to estimate risks of diabetes according to narrow categories of family history and adiposity separately for men and women with great precision.
Each of the 5 modifiable lifestyle factors was independently associated with risk for incident diabetes; increased adiposity displayed the strongest association. The likely causal effects of adiposity on diabetes risk do not deserve further elaboration here (13
). However, even after adjustment for adiposity, regular physical activity, a healthful diet, not smoking, and moderate alcohol use still predicted a lower risk for diabetes. This suggests that these lifestyle factors exert their effects on diabetes risk independent of their effects on adiposity. Since these lifestyle factors also exert at least part of their effects on diabetes risk through adiposity, adjustment for adiposity in these models may reflect overadjustment, underestimating the full impact of these lifestyle factors in the etiology of diabetes.
In the current study, compared to men and women who were not moderate drinkers, we observed a 19% and 37% lower risk of diabetes among moderate drinking men and women, respectively. Insulin resistance is an important factor in the development of diabetes, and light to moderate alcohol consumption has been associated with enhanced insulin sensitivity in several observational studies (24
). In a controlled trial among nondiabetic postmenopausal women, consumption of 30 g/day of alcohol for 8 weeks resulted in decreases in fasting insulin, as well as increases in triglycerides and insulin sensitivity (27
). Moderate alcohol consumption also has noted anti-inflammatory effects (28
), representing an additional mechanism by which moderate alcohol consumption may lower the risk of developing diabetes.
Multiple prospective cohort studies have determined the association between active smoking and risk for diabetes (30
). Much less is known about the influence of smoking cessation. In a recent study, diabetes risk was elevated in recent quitters, compared to never smokers, but decreased gradually to 0 after 12 years (31
). Among never smokers as well as those who successfully quit smoking for a decade or more before baseline, we observed a 24% and 16% reduction in risk of diabetes among men and women, respectively. Smoking negatively affects insulin sensitivity and pancreatic β-cell functioning (32
), has pro-inflammatory effects (34
), and increases central obesity (35
), all of which have been implicated in the development of diabetes.
We tested whether those who were overweight or obese, but otherwise followed a low-risk lifestyle pattern had a lower risk for developing diabetes. Our findings suggested that the remaining lifestyle factors were associated with a lower risk for diabetes among normal weight, overweight, and obese men and women. Similar inverse dose-response associations between a low-risk lifestyle profile and diabetes risk was observed irrespective of a family history of diabetes. The former findings imply, in the context of diabetes risk, that overweight and obese adults may benefit by adopting other low-risk lifestyle behaviors. The latter findings are particularly important given that many individuals may mistakenly believe that their family history of diabetes assures their own eventual development of diabetes; however, these individuals may at least delay the development of diabetes by achieving a healthy lifestyle.
The major strengths of the current study include its large sample size including men and women, its prospective design, and detailed epidemiologic profiles. A large number of diabetes cases permitted stratification by several characteristics simultaneously and provided increased power to detect modest associations with risk. However, this study also had some limitations. First, we had only a single baseline determination of the factors that contributed to the combined number of lifestyle risk factors with no consideration for changes in these factors that may have occurred prior to or after exposure assessment. Second, misclassification of some lifestyle risk factors, particularly diet and physical activity, is likely. Third, in a large study such as this, we had to rely upon a self-reported diagnosis of diabetes. The self-report of diabetes has shown substantial agreement when compared to medical records (kappa=0.76), high specificity (99.7%), but low sensitivity (66.0%) (36
). Individuals with a poor lifestyle may have experienced closer medical attention, potentially overestimating the occurrence of diabetes. In a compensating fashion, those with a healthier lifestyle may also have been more likely to have access to or seek medical attention, overestimating the incidence of diabetes among those with a healthy lifestyle. Fourth, the current study was limited to participants of the follow-up survey in 2004–2006. This may have induced a selection bias if the lifestyle risk factors included in the current study were associated with participation in the follow-up survey differentially by diabetes status. Finally, although we adjusted for major sociodemographic characteristics and lifestyle factors simultaneously, residual confounding by unmeasured or inadequately measured factors may exist. However, since many of the risk estimates were of substantial magnitude it is unlikely that all of the risk difference can be explained by residual confounding.
We found that a low-risk profile incorporating 5 lifestyle factors was strongly associated with a lower risk for new-onset diabetes among older adults. Each 1 additional factor in the low-risk group was associated with a substantial reduction in risk for diabetes. While this combined influence of lifestyle was slightly more strongly associated with a lower risk for diabetes among women, it was similarly observed among those with and without a family history of diabetes and those with higher and lower levels of adiposity. These results provide evidence for a tremendous combined impact of lifestyle on diabetes risk reduction in older adults. Public health efforts should continue to support the achievement and maintenance of an optimal body weight, adoption of healthy and attainable physical activity and dietary goals as well as preventing the initiation of smoking and promoting its cessation. Although there are appropriate concerns regarding the wide-spread public health recommendation of moderate alcohol use in the prevention of diabetes, this study supports guidelines that do not exclude alcohol use in moderation among those without contraindications.