Scientists have found that drinking two to three cups of coffee a day may significantly reduce your risk of developing dementia, but drinking more won’t help protect your brain any further.
A major study tracked 131,821 American nurses and health professionals for up to 43 years, starting when they were in their early 40s. During this time, 11,033 people – around 8% – developed dementia. But those who drank moderate amounts of caffeinated coffee or tea were notably less likely to be among them.
The protective effect was strongest in people aged 75 or younger, who saw their dementia risk drop by 35% if they consumed around 250mg-300mg of caffeine daily – roughly two to three cups of coffee. Crucially, drinking more than this didn’t provide any extra benefit.
Women in the study reported drinking around four and a half cups of coffee or tea per day when they joined, while men drank around two and a half cups. Those who drank more caffeinated coffee tended to be younger, but they also drank more alcohol, smoked and consumed more calories – factors that all have been found to increase dementia risk.
Interestingly, people who drank more decaffeinated coffee showed faster memory decline. Researchers believe this is probably because people switched to decaf after developing sleep problems, raised blood pressure, or heart rhythm disturbances – all of which are themselves linked to cognitive decline and dementia.
Why caffeine might protect the brain
There are sound biological reasons why caffeine could help keep our brains healthy. It works by blocking adenosine, a chemical that dampens the activity of brain messengers like dopamine and acetylcholine. These brain messengers (or neurotransmitters) can become less active as we age and in conditions such as Alzheimer’s disease, so caffeine’s stimulating effect may help counteract this decline.
Caffeine also appears to work through other mechanisms, including reducing inflammation and helping regulate blood sugar metabolism. People who did not have dementia (yet?) but drank more than two cups of coffee daily throughout their lives had lower levels of the toxic amyloid plaques, abundantly found in people’s brains who have Alzheimer’s disease.
Coffee and tea also contain many other beneficial compounds with antioxidant and blood vessel benefits which can all protect the ageing brain.
The American study found that only one to two cups of tea were linked to the best protection against dementia, which may reflect the fact that people in the US drink less tea than coffee overall. Green tea wasn’t examined separately, although most studies suggest it also protects against dementia.
Why does more caffeine stop being helpful? The researchers suggest it may be down to how our bodies break down coffee. Very high doses can also disrupt sleep and increase anxiety, which undermines any brain benefits.
A principle established back in 1908, known as the Yerkes-Dodson law, shows that when we become too stimulated – whether from anxiety or too much coffee – our mental performance starts to decline.
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The findings from professional healthcare workers may not apply to everyone. But when researchers combined results from 38 other studies, they found similar results: caffeine drinkers had a 6%-16% lower dementia risk than non-drinkers, with one to three cups of coffee being optimal. Good news for tea lovers – in this broader analysis, drinking more tea was linked to greater protection.
Moderate caffeine intake doesn’t increase long-term blood pressure risk and may even reduce cardiovascular disease risk, which shares many risk factors with dementia. However, people with very high blood pressure are advised to limit themselves to perhaps one cup a day.
It’s worth noting that using “cups” as a measure doesn’t account for how much caffeine these actually contain. Fresh beans brewed at home contain different amounts of caffeine and can affect cholesterol levels differently than instant coffee, for instance.
But you don’t need much to feel a benefit. Even low doses of 40mg-60mg can improve alertness and mood in middle-aged people who normally did not drink (much) caffeine. More is not always better.
Eef Hogervorst has done consultancies for media (including the BBC) and Proctor & Gamble on nutrients and cognitive function/dementia risk. And she has received funding from ARUK, ISPF and British Council /Newton Trust to investigate nutrition and dementia risk in Indonesia.
