Fizzy Drinks and Coffee May Raise Stroke Risk, But Tea and Water Could Lower It

Avid coffee drinkers beware: four drinks a day could be the safe limit.

That’s one of several conclusions from two recent studies conducted by the Interstroke research project.

After comparing the drinking habits of thousands of people from across the world who had experienced a stroke, the international group of researchers found that certain intakes of fizzy drinks, concentrated fruit juice and coffee were associated with an increased stroke risk. Regular tea and water consumption, however, appeared to decrease this risk.

The findings were published in the Journal of Stroke and the International Journal of Stroke. 

Juicebox

Between 2007 and 2015, the Interstroke project gathered data from 27,950 people (average age 61.7) in 27 countries. Around half of the participants had recently experienced their first stroke at the time of initial data recording; the other half had never had a stroke.

All participants were asked how often they drank certain beverages (tea, water, coffee, etc.,) per day. A “cup size” was standardized to 250 milliliters/ 8 fluid ounces.

After trawling through the data, the researchers observed that carbonated beverages and coffee (when consumed in high amounts) were associated with increased odds of ischemic stroke and intracerebral hemorrhage, while concentrated fruit juices were associated with increased odds of intracerebral hemorrhage (but not higher chances of ischemic stroke).

Fizzy drinks (containing either sugar or artificial sweeteners) were linked with a 22% increased chance of a stroke – a risk that increased sharply with 2 or more drinks a day. This link was strongest in participants from Eastern/Central Europe, the Middle East, Africa and South America.

Drinking more than 4 cups of coffee per day increased the chance of a stroke by 37%. There was no observed risk for lower caffeine intakes, though.

Concentrated fruit juices were linked with a 37% increased chance of intracranial hemorrhage. Two drinks a day appeared to triple this risk, and women seemed to be more susceptible.

Seven glasses a day keeps the doctor away

Fortunately, the habit of drinking more than seven cups of water a day was associated with a reduced odds of stroke caused by a clot.

This finding, in particular, supports the researchers’ hypothesis that the elevated stroke risks associated with coffee and other beverages are partly underpinned by dehydration.

“All beverages contain a varying proportion of water,” Andrew Smyth, a professor of clinical epidemiology at University of Galway and lead researcher on both studies, told Technology Networks. “Water is likely to improve how well hydrated an individual is, and that can impact the composition of blood.”

“For example, individuals that are dehydrated tend to have more viscous (thicker) blood – and perhaps that may be more likely to clot (and therefore lead to an ischemic stroke).”

High consumption of caffeine (five cups or more a day) can cause dehydration, as well as other issues like higher blood pressure.

“Many beverages contain caffeine and other substances that may increase blood pressure – and we know that blood pressure is a leading risk factor for stroke,” Smyth continued. “So perhaps, higher caffeine intake may increase blood pressure and lead to stroke.”

“Many of these beverages may also have sugar, sweeteners or other substances added during their production or at the time of consumption (sugar/syrup added to tea/coffee) that may introduce chemicals/substances beyond the content of the beverage itself,” he added. “For example, high sugar intake may increase the risk of diabetes or other cardiovascular changes that may impact the chance of stroke.”

Smyth and his colleagues also observed that all levels of tea drinking appeared to reduce the risk of having an ischemic stroke – drinking 3-4 cups of green tea per day was linked with a 27% lower chance – though only low-to-moderate consumption was associated with lower odds of intracerebral hemorrhage. They posit that these benefits may be partly due to the antioxidants found in tea.

“Some beverages (like tea and some types of coffee) contain naturally occurring antioxidants and other chemicals that may reduce the chance of stroke by impacting multiple disease pathways,” Smyth said.

Lovers of a British cuppa beware, though: Smyth and his colleagues observed that the reduced chance of a stroke from drinking tea was lost for the participants that added milk to their bitter beverage. The researchers suggest the dairy addition could be blocking the beneficial effects of the drink’s antioxidants.

References:

1. Smyth A, Hankey GJ, Damasceno A, et al. Carbonated beverage, fruit drink, and water consumption and risk of acute stroke: the INTERSTROKE case-control study. J Stroke. 2024. doi: 10.5853/jos.2024.01543 
2. Smyth A, Hankey GJ, Langhorne P, et al. Tea and coffee consumption and risk of acute stroke: The INTERSTROKE Study. Int J Stroke. 2024. doi: 10.1177/17474930241264685