How many cups of coffee and tea had the fewest strokes
2 to 3 cups of coffee a day, 3 to 5 cups of tea, or 4 to 6 cups of the two together came with the lowest stroke risk in a study of 365,682 UK adults aged 50 to 74 (Zhang, 2021). People who drank 2 to 3 cups of coffee and 2 to 3 cups of tea a day had a 32% lower stroke risk than people who drank neither (likely range 21% to 41% lower) (Zhang, 2021). The study can't show the drinks caused this. Every number links to its source.
The short version
- 2 to 3 cups of coffee a day, 3 to 5 cups of tea, or 4 to 6 cups of the two together came with the lowest stroke risk (Zhang, 2021).
- People who drank 2 to 3 cups of coffee and 2 to 3 cups of tea a day had a 32% lower stroke risk than people who drank neither (likely range 21% to 41% lower) (Zhang, 2021). In groups of the same size, that's about 2 strokes for every 3 among people who drank neither, or about 7 for every 10, likely 6 to 8 (Zhang, 2021).
- The estimated drop was smaller at 4 or more cups of coffee a day than at 2 to 3. Compared with no coffee, 4 or more cups came with an 8% lower stroke risk (likely range 2% to 14% lower) and 2 to 3 cups with 12% lower (likely range 6% to 16% lower). These figures don't show the two amounts differ (Zhang, 2021).
- The coffee question counted decaf. Compared with decaf drinkers, ground coffee drinkers had a 10% lower stroke risk (likely range 3% to 16% lower), and instant coffee drinkers didn't clearly differ. That doesn't show switching coffee changes your risk (Zhang, 2021).
- People said once how much they drank, and coffee and tea drinkers differed in other ways, so the study can't show the drinks prevent strokes (Zhang, 2021).
Cups a day and stroke risk
Each column looks at one drink, compares people with those who drank none of it, and allows for how much of the other drink they had. People in the coffee rows could also drink tea, and the other way round (Zhang, 2021).
| Cups a day | Coffee, vs no coffee | Tea, vs no tea |
|---|---|---|
| Less than 1, or 1 | 10% lower stroke risk (5% to 15% lower) (Zhang, 2021) | No clear difference (3% lower, likely range 11% lower to 4% higher) (Zhang, 2021) |
| 2 to 3 | 12% lower stroke risk (6% to 16% lower) (Zhang, 2021) | 16% lower stroke risk (10% to 21% lower) (Zhang, 2021) |
| 4 or more | 8% lower stroke risk (2% to 14% lower) (Zhang, 2021) | 16% lower stroke risk (10% to 21% lower) (Zhang, 2021) |
The ranges in brackets are the likely ranges. The percentages compare risks between groups; they aren't percentage points, and they aren't what any one person would gain. Cups were people's own count; the paper doesn't give a standard cup size or strength.
A smooth curve across all the amounts put the lowest stroke risk at 2 to 3 cups of coffee, 3 to 5 cups of tea, or 4 to 6 cups of the two together, counting both drinks in the total (Zhang, 2021). These are estimates from one study.
The study of 365,682 people
Researchers used the UK Biobank, which recruited adults across the UK between 2006 and 2010. They took the 365,682 aged 50 to 74 who hadn't had a stroke or dementia. Each said once, on a touchscreen, how many cups of coffee (including decaf) and of tea (including black and green) they drank a day. Over a median of about 11 years, 10,053 had a stroke, about 3 in 100 (Zhang, 2021).
- Against people who drank neither, people who drank 2 to 3 cups of coffee and 2 to 3 cups of tea a day had a 32% lower risk of any stroke (likely range 21% to 41% lower) and a 38% lower risk of ischemic stroke (likely range 25% to 49% lower), the more common kind in this study, with 5,630 cases (Zhang, 2021).
- Neither drink was clearly linked to hemorrhagic stroke, of which there were 1,815 cases (Zhang, 2021).
- The study allowed for factors including age, sex, ethnicity, income, education, BMI, smoking, alcohol, exercise, diet, sugary drinks, cholesterol, cancer, diabetes, coronary artery disease and high blood pressure (Zhang, 2021).
Where to start
- In this study, a moderate amount of coffee or tea came with lower stroke risk. The study can't tell whether starting, stopping or changing how much you drink would change your own risk.
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How far to trust these numbers
- This was one follow-up study that watched what people already drank. The authors say causality can't be inferred (Zhang, 2021).
- People said once, at the start, how much they drank, and habits may have changed over 11 years (Zhang, 2021).
- People who drank both coffee and tea were more often university-educated and on a high income than people who drank neither, and both drinks were linked to smoking, alcohol, exercise and health. The study adjusted for these, but the authors say other differences, such as sleep or genes, may remain (Zhang, 2021).
- UK Biobank volunteers tend to be healthier than other people, and 96% were white, so the results may not apply to other groups (Zhang, 2021).