Although this study didn’t prove that coffee or tea was the reason cases of stroke and dementia were lower in this population, the association is believable, says Douglas Scharre, MD, a professor of clinical neurology and psychiatry and the director of cognitive neurology at the Ohio State University Wexner Medical Center in Columbus. “Several studies have found an association between caffeine consumption and decreased risk of stroke, dementia, Alzheimer’s disease, and Parkinson’s disease,” he says. That’s good news to many of us, given that overall coffee consumption has gone up by 5 percent in the United States since 2015, according to the National Coffee Association. Nearly two out of three of us have coffee every day, with the average person downing just over three cups a day. Dementia is a general term for an impaired ability to remember, think, or make decisions that interferes with daily life and activities, per the CDC. In 2014, an estimated five million Americans had dementia, with Alzheimer’s disease being the most common type.
People Who Drank Coffee or Tea or a Combination Had a Lower Incidence of Stroke and Dementia
To examine how coffee or tea may impact the risk of stroke and dementia, investigators studied 365,682 participants between ages 50 and 74 from the UK Biobank. The Biobank is an international health resource that has collected blood, urine, and saliva samples along with other detailed health information for research purposes. The subjects were recruited between 2006 and 2010 and followed until 2020. During the study period, 5,079 people developed dementia and 10,053 experienced at least one stroke. Coffee and tea intake were reported by the participants at the start of the trial. After adjusting for many factors that could influence stroke or dementia risk, including sex, age, ethnicity, body mass index, physical activity, smoking status, and previously existing health conditions, investigators found the following:
People who drank two to three cups of coffee, or three to five cups of tea per day, or a combination of four to six cups of coffee and tea had the lowest incidence of stroke or dementia.Two to three cups of coffee with two to three cups of tea daily was associated with a 32 percent lower risk of stroke and a 28 percent lower risk of dementia compared with people who drank neither coffee nor tea.Coffee alone or in combination with tea was associated with lower risk of post-stroke dementia. Post-stroke dementia is a condition where symptoms of dementia occur after a stroke.
Researchers acknowledged limitations in the research. Relatively few people developed dementia or stroke during the study period, which can make it difficult to extrapolate rates accurately to larger populations. In addition, the trial was observational, and although coffee and tea consumption were associated with a lower incidence of dementia, stroke, and post-stroke dementia, the study wasn’t set up to prove causality. Although cause and effect hasn’t been established here, one possible explanation could be related to caffeine’s stimulating effect on the brain, which in turn impacts our mood and makes us more alert, says Dr. Scharre, who wasn’t involved in the study. “Stroke and dementia are both brain disorders; increased brain excitability may impact brain reserve and delay dementia,” he says. Caffeine seems to have some impact on stroke risk factors, though it could also be that people who drink caffeine are also people who are more likely to find ways to reduce stroke and dementia risk factors, says Scharre. Previous studies have shown that coffee was associated with a decreased risk of heart failure, according to the American Heart Association (AHA). There is evidence that heart failure is associated with an increased short-term and long-term risk of stroke, according to a study published in Stroke journal in April 2017.
Coffee Can Be Part of a Healthy Diet for Most People
Drinking up to 400 milligrams (mg) of caffeine a day isn’t associated with negative or dangerous health effects, according to the U.S. Food and Drug Administration (FDA). The average cup of green or black tea has 30 to 50 mg of caffeine, and an 8 ounce cup of coffee has about 80 to 100 mg. But you can have too much of a good thing — too many cups of coffee or tea can cause insomnia, jitters, anxiousness, and an upset stomach. And keep in mind that the recommendations for coffee are for black coffee: The AHA warns that many coffee-based drinks have a lot of added fats and sugar and are high in calories.
