March 10, 2011 — Drinking 1 to 5 cups of coffee a day was associated with a 22% to 25% lower risk for stroke in a large group of Swedish women followed up for an average of about 10 years, according to research released today.
"There was no dose-response relationship between coffee consumption and risk for total stroke, rather the risk appeared to be increased among women with low or no coffee consumption," the study team notes in the March 10 online issue of Stroke.
Because coffee is one of most widely enjoyed beverages in the world, "even small health effects of substances in coffee may have large public health consequences," Susanna Larsson, PhD, lead author of the study and a researcher in the Division of Nutritional Epidemiology, National Institute of Environmental Medicine, Karolinska Institute in Stockholm, Sweden, noted in a statement.
Swedish Mammography Study
Dr. Larsson and her colleagues analyzed data on 34,670 women in the prospective, population-based Swedish Mammography Study who were free of cardiovascular disease in 1997. As part of the study, the women completed a food-frequency questionnaire at baseline.
During a mean follow-up of 10.4 years, a total of 1680 stroke events were documented, including 1310 cerebral infarctions, 154 intracerebral hemorrhages, 79 subarachnoid hemorrhages, and 137 unspecified strokes.
After adjusting for known cardiovascular risk factors, including smoking status and pack-years, education, body mass index, physical activity, aspirin use, history of diabetes, hypertension, or alcohol consumption, coffee consumption was associated with a lower risk for total stroke, cerebral infarction, and subarachnoid hemorrhage, but not intracerebral hemorrhage, possibly due to the small number of cases.
Table. Multivariate Adjusted Relative Risk for Stroke (95% Confidence Interval) by Coffee Intake
| Stroke Type | 1 – 2 Cups Daily | 3 – 4 Cups Daily | ≥5 Cups Daily | P for Trend |
| Total stroke | 0.78 (0.66 – 0.91) | 0.75 (0.64 – 0.88) | 0.77 (0.63 – 0.92) | .02 |
| Cerebral infarction | 0.79 (0.66 – 0.94) | 0.80 (0.66 – 0.96) | 0.79 (0.63 – 0.98) | .08 |
| Total hemorrhagic | 0.83 (0.54 – 1.26) | 0.61 (0.39 – 0.94) | 0.67 (0.40 – 1.13) | .08 |
| Intracerebral hemorrhage | 0.95 (0.55 – 1.65) | 0.77 (0.44 – 1.36) | 1.07 (0.56 – 2.03) | .86 |
| Subarachnoid hemorrhage | 0.68 (0.35 – 1.32) | 0.40 (0.20 – 0.81) | 0.27 (0.11 – 0.67) | .002 |
Reference was fewer than 1 cup daily.
Interpret Cautiously
Reached for comment, Larry B. Goldstein, MD, director of the Stroke Center at Duke University in Durham, North Carolina, and national spokesperson for the American Stroke Association, said "association studies, like this one, are of some general interest; however, you have to be careful not to make too much out of them, the basic rule being that association never proves causality.
"There always can be unmeasured factors that can be contributing to the difference," he noted. "In this particular study, the researchers used a nutrition questionnaire administered in 1997 and then followed people forward looking for future events. So you don't know about how or if their behavior has changed over time."
Like Dr. Larsson's team, Dr. Goldstein also made note of the lack of a dose-response effect in this study. "Something that supports causality, but again doesn't prove it, is a dose-response effect, which didn't really appear in this study," Dr. Goldstein noted. "However, there could be a threshold effect."
The study also did not control for caffeine content of the coffee or how the coffee was processed. "There are so many factors in this type of study that limit drawing strong conclusions," Dr. Goldstein said.
Dr. Larsson and colleagues agree that no firm conclusions can be drawn from this study. They say coffee consumption could potentially reduce the risk for stroke by increasing insulin sensitivity and reducing inflammation.
The phenolic compounds of coffee have antioxidant properties and may improve endothelial function. They emphasize, however, that epidemiologic studies of coffee consumption and stroke have yielded inconsistent results.
Dr. Goldstein said it's "not surprising" that the literature on coffee consumption and stroke is mixed. "It's mixed because of the different populations studied and different study designs; some studies have suggested benefits, or at least no risk, from drinking coffee."
Dr. Larsson and colleagues say additional prospective studies on coffee consumption and stroke incidence and mechanistic studies investigating possible effects of coffee drinking on cardiovascular risk factors are warranted.
The study was supported by the Swedish Council for Working Life and Social Research and the Swedish Research Council for Infrastructure. The researchers and Dr. Goldstein have disclosed no relevant financial relationships.
Stroke. Published March 10, 2011. Abstract
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