Women who drink more than one cup of coffee per day appear to have a 22 to 25% lower risk of stroke compared to women who drink less, according to new research from Sweden reported in Stroke: Journal of the American Heart Association.

Lead author Dr Susanna Larsson, a researcher in the Division of Nutritional Epidemiology, National Institute of Environmental Medicine, Karolinska Institute in Stockholm, and colleagues examined data that followed more than 30,000 women for 10 years.

They found that low or no coffee drinking was linked to an increased risk of stroke.

They commented that although this is not enough reason to change coffee-drinking habits, it should ease concerns about this highly popular drink.

Because coffee is one of the most widely consumed beverages in the world, even small health effects from the substances it contains may have large consequences for public health, Larsson said in a statement.

Previous studies have looked at links between coffee consumption and risk of stroke and death, but with inconsistent results, wrote the authors in their background information.

For this study, they looked at data on 34,670 women without a history of cardiovascular disease in 1997 when the study started. The women were aged from 49 to 83 years and were followed for an average 10.4 years as participants in the Swedish Mammography Cohort, an epidemiological study looking at links between diet, lifestyle and disease development.

Information about coffee consumption came from food frequency questionnaires that the women filled in at the start of the study. Information about stroke incidence came from records in the Swedish Hospital Discharge Registry covering the period from the beginning of 1998 to end of 2008. The Registry is almost a complete record of Swedish hospital discharges.

The results showed that:
  • Over a mean follow up of 10.4 years, there were 1,680 various types of stroke events, including: 1,310 cerebral infarctions (eg from a blocked blood vessel in the brain), 154 intracerebral hemorrhages (eg spontaneous bleeding in brain tissue), 79 subarachnoid hemorrhages (bleeding into the space surrounding the brain), and 137 unspecified strokes.

  • After adjusting for other risk factors, consumption of coffee was linked to a statistically significant extent with a lower risk of total stroke and also with cerebral infarction and subarachnoid hemorrhage, but not with intracerebral hemorrhage.

  • The relative risk of stroke was not lower for consumption of less than one cup per day.

  • The relative risk of stroke was lower for consumption of 1 to 2 cups per day, 3 to 4 cups per day, and 5 cups a day and higher.

  • These were respectively: 0.78 relative risk or RR for 1-2 cups (95% confidence interval CI ranged from 0.66 to 0.91), 0.75 RR for 3-4 cups (95% CI, 0.64 to 0.88), and 0.77 RR for 5 cups and over (95% CI, 0.63 to 0.92), with P for trend=0.02.

  • The link between coffee consumption and cerebral infarction was unaffected when examined in relation to smoking status, body mass index, history of diabetes or high blood pressure, or consumption of alcohol.
The researchers concluded that:

"These findings suggest that low or no coffee consumption is associated with an increased risk of stroke in women."

Larsson said the questionnaire did not distinguish between caffeinated and decaffeinated coffee, but they knew from other sources that consumption of decaffeinated coffee is low in Sweden, implying that the results would not have changed significantly if they had been able to take out the effect of decaffeinated consumption.

Speculating on how drinking coffee might reduce the risk of stroke, Larsson suggested it might weaken subclinical inflammation, reduce oxidative stress and improve insulin sensitivity.

A potential weakness of the study is that the data on coffee consumption and medical history came from responses to questionnaires that the women filled in by themselves, which is a known cause of measurement error and leads to a potentially higher chance that some women end up in the wrong coffee consumption category.

It is also possible that the effect seen in this study is due to some yet unknown factor that is also linked to low or moderate coffee consumption, explained Larsson.

However, she said while some women have been avoiding coffee because they think it is unhealthy, the fact is there is an increasing body of evidence that shows drinking coffee in moderation can reduce the risk of diseases like diabetes, liver cancer and maybe even stroke.

She said we now need more studies to confirm these findings.

Related reading: Drinking Coffee: More Good Than Harm? (9 July 2012)

Written by: Catharine Paddock, PhD