A major US study links moderate tea and coffee intake to reduced dementia risk over four decades
A simple daily ritual shared by millions could be quietly shaping brain health for decades. According to a major US study, people who regularly drink modest amounts of tea or coffee appear to face a significantly lower risk of developing dementia later in life.
Scientists analysing long-term health data found that adults who consumed two to three cups of caffeinated coffee a day or one to two cups of caffeinated tea had a 15 to 20 per cent lower risk of dementia compared with those who avoided the drinks altogether. The findings span more than 40 years of follow-up, making it one of the most extensive investigations into caffeine and cognitive health to date.
The research also revealed that coffee drinkers showed slightly better cognitive performance over time. Those who chose caffeinated coffee experienced marginally less cognitive decline and performed better on certain objective brain function tests than people who drank decaffeinated coffee.
The study, published in the Journal of the American Medical Association, drew on data from 131,821 participants enrolled in two long-running US health projects, the Nurses’ Health Study and the Health Professionals Follow-Up Study. Participants repeatedly reported their diets, health conditions and cognitive changes, allowing researchers to track patterns over decades rather than years.
Despite the striking association, scientists stress that the results do not prove that tea or coffee directly protects the brain. People who drink caffeine may differ in important ways from those who avoid it. For example, individuals with poor sleep, which itself is linked to higher dementia risk, may deliberately cut out caffeine, unintentionally skewing results.
Lead author Yu Zhang of Harvard University said the study offers the strongest evidence so far but stops short of establishing cause and effect. He explained that the findings align with known biological mechanisms, making the link plausible even if not definitive.
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Tea and coffee contain caffeine and polyphenols, compounds believed to support brain health by improving blood vessel function and reducing inflammation and oxidative stress. Oxidative stress occurs when unstable molecules damage cells, a process closely linked to ageing and neurodegeneration. Caffeine has also been associated with improved metabolic health and lower rates of type 2 diabetes, itself a known risk factor for dementia.
The analysis showed that dementia risk reduction appeared to plateau. Drinking more than two to three cups of caffeinated coffee or one to two cups of tea did not seem to offer additional protection. Crucially, no protective effect was found for decaffeinated coffee, suggesting caffeine plays a central role.
Experts caution that proving direct benefit would require randomised trials assigning people to caffeinated or non-caffeinated drinks for decades, something widely regarded as impractical. Instead, future research may focus on identifying biological changes in the brain linked to caffeine intake using scans or biomarkers.
Professor Naveed Sattar of the University of Glasgow highlighted the complexity of caffeine’s effects. While antioxidants and mild stimulation may encourage physical activity and learning, caffeine can also raise blood pressure in some individuals, a major contributor to dementia risk. The balance of benefits and harms likely varies from person to person.
Scientists estimate that up to half of dementia cases worldwide could be prevented or delayed by addressing known risk factors such as obesity, smoking, excessive alcohol use, hearing loss and high blood pressure.
Zhang urged caution against viewing tea or coffee as a cure. He emphasised that brain health depends on a wider lifestyle picture, including regular exercise, balanced nutrition and quality sleep.
For now, the evidence suggests that enjoying a couple of teas or coffees a day may offer more than comfort. It could be quietly supporting the brain through the long arc of ageing, even if it is only one piece of a much larger puzzle.