It’s just a correlation, no cause-effect relationship has been proven yet, but researchers report that drinking 4-6 cups of tea and/or coffee a day was associated with substantially lower risks of stroke and dementia.

Every day, billions of people enjoy one or several cups of either coffee or black tea. To some, it’s become an almost necessary ritual where you need it to start your day. The impact of coffee and tea on human health is somewhat controversial, with studies finding both potential benefits and downsides to the drinks — especially coffee.

Yuan Zhang and colleagues from Tianjin Medical University, Tianjin, China wanted to assess the links between drinking tea and coffee and two of the most prevalent health problems in the world: stroke and dementia.

Not only are strokes and dementia severe conditions by themselves, but they are sometimes linked as well. For instance, post-stroke dementia can occur in 6% to 32% of stroke cases.

People who drank 2-3 cups of coffee or 3-5 cups of tea per day (a cup of coffee generally has 3-4 times the caffeine amount of a cup of tea) reported a significant risk of both stroke and dementia. However, those who drank both coffee and tea (a combination of 4-6 cups per day) had the lowest risk — a 32% lower risk of stroke and 28% lower risk of dementia than those who drank neither coffee nor tea.

“Our findings suggested that moderate consumption of coffee and tea separately or in combination were associated with lower risk of stroke and dementia,” the researchers write in the study.

The study was carried out on a sample of over 360,000 participants from the UK Biobank — a large, long-term study in the UK investigating how genetics and lifestyle factors relate to the development of the disease. The UK Biobank was designed to reflect a relatively healthy population, and it is, of course, based largely on the UK population. This means that the findings may not be representative of other populations. Overall, 5,079 participants developed dementia and 10,053 experienced at least one stroke — a large sample size that offers a good degree of statistical significance.

However, just because there is a correlation between stroke, dementia, and drinking coffee and tea, doesn’t mean there’s a direct cause-effect relationship. There could be other aspects at play that have not yet been uncovered — this is still a matter of investigation.

Nevertheless, this is not the first time the two beverages have been linked with healthy effects on the body, although more research is required to establish a cause-effect relationship.

“These findings highlight a potential beneficial relationship between coffee and tea consumption and risk of stroke, dementia, and post-stroke dementia — although causality cannot be incurred,” the researchers conclude.

The study has been published in PLOS.