The study was the work of Dr Esther Lopez-Garcia, from the School of Medicine, Universidad Autonoma de Madrid in Spain, and colleagues in Spain and the US, and was published online before print in the February 16 issue of Circulation: Journal of the American Heart Association.
The authors wrote in their background information that there was very little research on any potential link between coffee consumption and stroke risk.
For this study, Lopez-Garcia and colleagues analyzed data from the Nurses' Health Study. The data covered 83,076 women who were followed for 24 years, starting with the first assessment of coffee consumption in 1980. This assessment was repeated every 2 to 4 years until 2004.
None of the women had a history of stroke, coronary heart disease, diabetes, or cancer at the start of the study.
The main outcome measure was the number and type of strokes that occurred among the women during the follow up.
Using statistical tools like Cox regression models, the researchers analyzed the relative risks (RR) between the stroke events and coffee consumption, while ruling out potential confounders such as age, smoking status, body mass index (BMI), exercise/physical activity, use of alcohol, menopausal status, use of hormone therapy, use of aspirin, and other dietary factors.
The results showed that:
- Over the follow up period, there were 2,280 strokes: 426 of which were hemorrhagic (burst blood vessel in the brain), 1,224 ischemic (loss of blood supply to the brain), and 630 undetermined.
- The relative risk of stroke went down as coffee consumption went up.
- For women who drank between 1 cup of coffee a month and 4 cups per week, the relative risk of stroke was 0.98 compared to women who drank less than one cup a month.
- For women who drank 5 to 7 cups of coffee a week, the relative risk of stroke was 0.88.
- For 2 to 3 cups a day the relative risk was 0.81, and for more than 4 per day it was 0.80.
- After adjusting the figures again to take into account high blood pressure, high blood cholesterol and type 2 diabetes, the relative risk of stroke still showed the same inverse association with coffee consumption: it went down as coffee consumption went up.
- The association was stronger among women who had either never smoked or had given up than among current smokers .
- Stroke risk was not linked to consumption of other drinks containing caffeine such as tea and caffeinated soft drinks.
- After taking out the effect of caffeinated coffee drinking, increasing decaffeinated coffee consumption was also found to be linked to lower stroke risk (relative risk of 2 or more cups a day compared to less than 1 a month was 0.89).
"Long-term coffee consumption was not associated with an increased risk of stroke in women. In contrast, our data suggest that coffee consumption may modestly reduce risk of stroke."
It would appear from these results that the beneficial link is not due to caffeine. WebMD reported that Lopez-Garcia suggested it was other ingredients in coffee that may be responsible for the lower risk of stroke as consumption rises:
"Antioxidants in coffee lower inflammation and improve blood vessel function," she said in a press statement.
However, Lopez-Garcia cautioned that the beneficial effect of coffee drinking only applies to healthy people. Increasing coffee consumption will not make existing stroke risk from other causes go away.
And anyone with health problems should talk to their doctor about their own specific risk, she said. For instance people suffering with blood pressure, heart problems, anxiety or insomnia may not benefit from drinking coffee.
Related reading: Drinking Coffee: More Good Than Harm? (9 July 2012).