Data from this large prospective cohort study in men do not support a strong association between alcohol consumption and risk of incident stroke or functional outcome after stroke. Our data suggest lowest risks of incident TIA and total, ischemic or hemorrhagic stroke among men who consume 1 alcohol drink per week. However, this decrease in risk only reached statistical significance for total stroke. When examining the relationship between alcohol consumption and short-term functional outcomes after stroke, most of the categories of alcohol consumption did not show a statistically significant association with functional outcomes after stroke. Only men who consumed 1 drink per week had a significantly decreased risk of having an mRS score of 4 to 6 (ie, the most severely affected group) as compared with men who had no stroke or TIA and who consumed less than 1 drink per day.
Our results with regard to the association between alcohol consumption and stroke incidence are somewhat different from those found in an earlier study of the relationship between alcohol consumption and risk of stroke using PHS data.6 Berger et al found that men who consumed 2 to 4 alcohol drinks per week had a statistically significant decreased risk of total and ischemic stroke. The differences in the results between our study and Berger’s study and other studies that have also shown statistically significant decreased risk of stroke among light to moderate drinkers18,19 may be explained by the longer follow-up time and, thus, the aging of the cohort. Moderate to light alcohol consumption may reduce the risk of stroke in shorter follow-up periods but has reduced influence in long periods.
Only a few studies have looked at the effect of prestroke alcohol consumption on functional stroke outcomes. The North East Melbourne Stroke Incidence Study (NEMESIS) did not find prestroke alcohol consumption to be a factor that independently predicted handicap 2 years after stroke in multivariate analysis.8 The Copenhagen Stroke Study examined a population of patients with severe stroke to determine factors that predicted good outcome after rehabilitation. Daily alcohol consumption compared to nondaily alcohol consumption was an independent predictor of good outcome only in univariate but not in multivariate analysis.7Our study shows similar results to NEMESIS and the Copenhagen Stroke Study and extends their findings because the large number of participants and outcome events allow us to use finer categories of alcohol consumption and functional stroke outcome. Additionally, our results are not limited to only the most severe cases of stroke.
We used the mRS scores as a measurement of functional outcome from stroke. Although the mRS claims to be a measure of handicap, its strong emphasis on mobility makes it more a measure of disability or a “global health index.”20,21 Despite its limitations,22,23 the mRS score is widely accepted for use in clinical trials and is an appropriate outcome measure for this study. The mRS is simple to administer, can be assessed retrospectively from medical records, and has strong test–retest reliability, interrater reliability, and validity.23 Additionally, the mRS can be used to compare patients with many different types of neurological limitations and allows prestroke disability to be taken into consideration when determining poststroke Rankin score.15 Another advantage to mRS is that it does not seem to have a “ceiling effect” as can sometimes be observed when using the Barthel Index.24
Other strengths to our study include the large number of participants and outcome events, prospective design, confirmed outcome definition with high interobserver agreement,14 and the homogenous structure of the cohort, which limits confounding by access to medical care.
One limitation to our study is the possible bias arising from the use of self-reported alcohol consumption. However, misclassification of alcohol consumption at baseline is most likely nondifferential because of the prospective design. Only using alcohol consumption at baseline may not accurately reflect alcohol consumption over the course of the study. However, we found a high correlation between alcohol consumption at baseline and at 84 months (r=0.75). In addition, when we evaluated the association between alcohol consumption and risk of stroke and functional outcomes from stroke using alcohol consumption at 84 months and cases of stroke after 84 months, we found very similar results (data not shown). We combined the 2 highest alcohol intake categories because only a few physicians drank >1 drink per day, which may have masked potential harmful effects. However, dividing the highest category of alcohol consumption (≥1 drink/d) into 2 categories (1 drink/d and ≥2 drinks/d) did not reveal any further increased or decreased risk of our functional outcomes (data not shown).
Using nondrinkers as the reference category when examining the relationship between alcohol consumption and risk of stroke or functional outcomes from stroke has been questioned because of the potential for ex-drinkers who quit for health reasons to be included in the nondrinkers category. Including ex-drinkers in the nondrinker category may result in an attenuation of the relationship between alcohol consumption and risk of stroke or functional outcomes from stroke. However, the inclusion of many ex-drinkers in the nondrinker category is unlikely in this cohort because the men were free of many disabling conditions and of major diseases at baseline that could lead one to abstain from alcohol.
Having limited information about the men’s functional status prestroke is unlikely to be a large source of bias. In general the men were most likely healthy and able-bodied because they had to be free of many major diseases to be included in the study base. Additionally, the mRS scale takes prestroke disability into account when measuring functional outcomes from stroke.
Another limitation is that because very few men in our study were underweight, we are unable to make any inferences about possible interactions between body weight and alcohol consumption on our functional outcomes.
Our study participants were all male physicians who presumably live a healthier lifestyle compared to the general population. Thus, our results may not be generalizable to other populations and we cannot exclude potential harmful effects of very high alcohol consumption on the evaluated outcomes. Because gender differences in alcohol metabolism may exist25 and women have different risk factors for stroke and poorer outcomes from stroke than men,26 future research will need to examine the association of alcohol consumption on the risk of stroke and functional outcomes from stroke among women.
In conclusion, our data do not show strong association between alcohol consumption, which is a component of the lifestyle of many individuals, with risk of incident stroke or functional outcome after stroke. A modest beneficial association was observed for those men who had low alcohol consumption. Future studies are warranted to evaluate potential factors influencing functional outcome after stroke.
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