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In the news: Do Coffee + Tea Act Synergistically to Lower Stroke & Dementia Risk?

Coffee & Tea Lowers Stroke & Dementia Risk

While previous studies have reported significant health benefits from moderate intake of coffee and tea separately, few have investigated the effect of drinking both.

Researchers from Tianjin Medical University and Yale School of Public Health have now examined the effects of coffee or tea, or their combined intake on stroke and dementia – two conditions of increasing global health concern, and both of which can impact vision.

The study(1) included 365,682 participants (50 to 74 years old) from the UK Biobank who reported their coffee and tea consumption. Participants were recruited for the study from 2006 to 2010 and were followed until 2020.

During a median follow-up of 11.4 years for new onset disease, 5,079 participants developed dementia, and10,053 participants experienced stroke.

After adjusting for confounders, coffee intake of 2 - 3 cups/day or tea intake of 3 - 5 cups/day or their combined intake of 4 - 6 cups/day were linked to a reduced risk of incident stroke and dementia.

The benefits were greatest for those who drank both coffee and tea. Compared with those who did not drink tea and coffee, drinking 2 to 3 cups of coffee and 2 to 3 cups of tea daily was associated with a 32% lower risk of stroke (P < 0.001) and a 28% lower risk of dementia (P = 0.002).

Drinking both beverages was also tied to a lower risk of ischemic stroke and vascular dementia, Again, their combined consumption provided greater benefit than coffee or tea alone.

Importantly, the combination of tea and coffee was associated with a lower risk of poststroke dementia. Those who have had a stroke have a far greater risk of developing dementia than those who have not.

For participants who experienced a stroke during the follow-up period, drinking 2-3 cups of coffee daily was linked to a 20% lower risk for poststroke dementia (P = .04) while drinking both beverages (3 to 6 cups of coffee and tea daily) lowered the risk of post stroke dementia by 48% (P = .007).

No significant association between coffee and tea consumption and risk for hemorrhagic stroke or Alzheimer’s disease was observed.

“These findings highlight a potential beneficial relationship between coffee and tea consumption and risk of stroke, dementia, and poststroke dementia, though causality cannot be inferred” wrote the authors.

Coffee contains caffeine and is a rich source of antioxidants and other bioactive compounds, while tea provides catechin polyphenols, and flavonoids. Coffee and tea are distinct beverages with overlapping components such as caffeine, but also different biologically active constituents with different target molecules and therefore different biological effects. The findings of this study suggest a possible synergistic effect of these common beverages relevant to stroke and dementia.

In terms of mechanisms, a new study(2) from UC Irvine shows that compounds in green and black tea relax blood vessels by activating ion channel proteins in the vessel wall – a discovery that helps explain the anti-hypertensive properties of tea. This is relevant because individuals with high blood pressure are more likely to have a stroke than those with normal blood pressure.

Caffeine might help counter dementia. One theory is that hypoxia (which leads to cognitive impairment) triggers the release of adenosine, which in turn causes a chain reaction of enzymes leading to inflammation. Caffeine interferes with this by blocking the cells' ability to recognize adenosine, reducing inflammation.

References

1. Yuan Zhang, et al. Consumption of coffee and tea and risk of developing stroke, dementia and poststroke dementia: A cohort study in the UK Biobank. Plos Medicine. Nov, 2021.
2. Redford KE, et al. KCNQ5 potassium channel activation underlies vasodilation by tea. Cellular Physiol Biochem. 6;55(S3):46-64, 2021.