In these two populations of US health professionals, individuals with a low-risk lifestyle (not smoking, exercising daily, consuming a prudent diet including moderate alcohol and having a healthy weight during mid-life) had a significantly lower risk of stroke than individuals without a low-risk lifestyle. These estimates were driven mainly by lower risk of ischemic, rather than hemorrhagic, stroke. Within these study populations, approximately half of ischemic stroke could be attributed to unhealthy lifestyle factors.
A combination of lifestyle factors has been associated with substantially lower risk of many chronic diseases within these and other populations. In the NHS, 70% of total CVD3
, 80% of CHD3
and 90% of diabetes5
were attributed to not following a low-risk lifestyle defined by these same five factors. In the HPFS, 62% of CHD and 79% of CHD among men <65 were attributed to these same 5 factors4
. Among men and women ≥70 years old, 61% of cardiovascular deaths may have been avoided through a healthy diet, moderate alcohol, daily exercise and not smoking7
While many studies have focused on low-risk characteristics and risk of total CVD, fewer studies have addressed the impact of these characteristics on stroke exclusively. In the Women’s Health Study, a prospective cohort study of 37,636 women followed for 10 years, women with the healthiest lifestyle score, defined as never smoked, BMI<22 kg/m2
, exercising ≥4 times/week, consuming ½ to 1 ½ drinks/day and following a healthy diet had a RR of 0.29 (95%CI: 0.14, 0.63) for ischemic stroke compared to women with the least healthy lifestyle20
. Similarly, we found a RR for ischemic stroke of 0.19 in women and 0.21 in men, comparing the healthiest to least healthy individuals. Lifestyle likely influences the risk of stroke in part through clinical risk factors, including hypertension and diabetes. In the EPIC Potsdam study, almost 60% of ischemic stroke cases could be attributed to hypertension, diabetes, hypercholesterolemia, smoking and heavy alcohol consumption (>15 g alcohol/day in women; >30 g alcohol/day in men)27
. Stamler et al found a low-risk lifestyle, defined as cholesterol<200 mg/dl, blood pressure<120/80 mmHg and not smoking, was associated with 52–76% lower risk of total stroke mortality in several cohorts, although the analyses were limited by few stroke deaths (<15 in any cohort)28
We found that mid-life BMI was a stronger predictor of stroke than current BMI, as seen with other diseases29–31
. The association between obesity and risk of chronic disease is complicated and can be obscured by reduction in body weight due to pre-clinical or chronic disease. BMI measured during mid-life may be less influenced by underlying disease processes and may more accurately reflect the true relation between body weight and stroke risk31
. Additionally, the loss of lean body mass with age, may lead to a reduction in BMI but an increase in percent of body fat. In this case, BMI may no longer capture the impact of adiposity on disease risk32
. Because strokes often occur among the elderly, other measures, such as waist circumference or waist:hip ratio, may provide better assessment of obesity-related risk33–35
Although the impact of alcohol on stroke risk is unclear, we included moderate alcohol intake in our low-risk lifestyle. While heavy alcohol consumption (>2 drinks/d) may increase risk of stroke, the evidence for light to moderate alcohol intake has been mixed, showing both null and inverse associations with ischemic stroke risk36
. In this study, we found a J-shaped association for both ischemic and hemorrhagic stroke, with increased risk at heavier quantities of alcohol. This study supports previous evidence that moderate alcohol consumption is not associated with greater risk of stroke, and may provide additional benefit in stroke prevention. Moderate alcohol may be considered part of a healthy lifestyle for overall chronic disease prevention, including stroke, when consumed responsibility and not contraindicated by other factors.
We explored the association of several dietary patterns on stroke risk. We focused on the AHEI-based diet score, which is associated with a 30–40% lower risk of CVD16
. Additionally, we explored a dietary score based on the low-sodium DASH diet, due to its beneficial impact on blood pressure in clinical trials19
and a previously defined 6-nutrient diet score, which was unexpectedly associated with a greater risk of stroke in the WHS20
. All three diets encompass an overall healthy dietary pattern, and adherence to any of these diets may contribute to the prevention of stroke risk.
Our low-risk lifestyle was not significantly associated with risk of hemorrhagic stroke, consistent with results from the WHS analysis20
. Individually, these lifestyle factors were more strongly associated with risk of ischemic than hemorrhagic stroke, although power was limited by the few hemorrhagic stroke cases. Future studies should focus on differences in risk factors between stroke types to enhance prevention strategies for both ischemic and hemorrhagic stroke. Likewise, we did not have adequate power to assess the impact on thrombotic stroke subtypes, such as lacunar v. large artery strokes.
Limitations of our study warrant discussion. As in any observational study, measurement error in self-reported variables is inevitable; however, misclassification in this prospective study should be non-differential with respect to disease status and would underestimate the true relative risk. Furthermore, a key strength of these participants is the high level of education and health interest, which has led to high quality and valid information through self-administered questionnaires11–14
. Although we attempted to control for any potential confounding variables, the possibility of residual confounding remains.
The PAR% is a population specific calculation, dependent on the prevalence of the exposure as well as its association with disease risk. The risk estimates between lifestyle factors and stroke are most likely generalizable to other populations, as the underlying biology should be similar across ethnicity, race and geography. However, the PAR% most likely underestimates the burden of unhealthy behavior on risk of stroke in the general population because the prevalence of these low-risk factors, and more importantly prevalence of extreme levels of unhealthy behaviors, is greater in the US population than in our cohorts. For example, the prevalence of US adults with a BMI under 25 is 32%, compared to 59% of women and 46% of men in our cohorts and 32% of adults in the US are obese (BMI ≥30) compared with only 11% of women and 8% of men in these populations37
. Greater benefit is likely to be gained by adherence to healthy lifestyle choices in populations with a less healthy lifestyle than in these populations of health professionals.
In conclusion, we found that a low-risk lifestyle is associated with lower risk of stroke, especially ischemic stroke, which adds to the data on the prevention of multiple chronic diseases, including CHD and diabetes. This study further supports the beneficial impact of a low-risk lifestyle on the primary prevention of chronic disease and long-term well-being.