Coffee and Tea Linked to Lower Dementia Risk in 43-Year Harvard Study

Drinking two to three cups of caffeinated coffee or one to two cups of tea a day is associated with a significantly lower risk of dementia, according to a 43-year study of more than 131,000 adults published in the Journal of the American Medical Association.

The finding carries particular weight in Australia. The Australian Bureau of Statistics confirmed in late 2025 that dementia had overtaken ischaemic heart disease as the country's leading cause of death, accounting for 9.4 per cent of all deaths in 2024. An estimated 446,500 Australians are living with the condition, a figure projected to exceed one million by 2065.

The research, led by investigators at Mass General Brigham, the Harvard T.H. Chan School of Public Health and the Broad Institute of MIT and Harvard, drew on two of the longest-running cohort studies in American medicine. The Nurses' Health Study has tracked 86,606 women since 1980, and the Health Professionals Follow-Up Study has tracked 45,215 men since 1986. Participants were followed for a median of 36.8 years, with dietary intake reassessed every two to four years. Over that time, 11,033 of them developed dementia.

Those in the highest quartile of caffeinated coffee intake had an 18 per cent lower risk of dementia than those with the lowest intake. Heavy tea drinkers saw a 16 per cent reduction. Decaffeinated coffee showed no such effect, which the authors take as evidence that caffeine itself, along with bioactive compounds specific to caffeinated beverages, is doing the work.

The benefits also plateaued. More was not better. The strongest associations were observed at moderate intake, and pushing beyond three cups a day did not appear to add any further protection.

Lead author Yu Zhang, a PhD student at the Chan School and research trainee at Mass General Brigham, said the relationship held across the genetic spectrum. Comparing participants with different inherited risk profiles produced the same results, suggesting coffee or caffeine is "likely equally beneficial" for people with high and low genetic predisposition to dementia.

A subset of the Nurses' Health Study cohort also completed telephone-based neuropsychological testing, including the Telephone Interview for Cognitive Status. On both objective and subjective measures, heavier caffeinated coffee drinkers performed modestly better, although the association with broader global cognition fell just short of statistical significance.

Senior author Daniel Wang of Mass General Brigham and the Chan School was careful to qualify the results. The effect size is small, he said, and caffeinated coffee or tea consumption is at best "one piece of that puzzle" in a broader approach to protecting cognitive function with age.

Independent experts echoed that caution. Dr Mohammad Talaei of Queen Mary University of London, commenting via the Science Media Centre, noted that dementia has a long prodromal phase and that declining coffee intake can itself be an early symptom of cognitive change. Some of the association may therefore reflect reverse causation rather than a protective effect. Sleep disruption and cardiovascular health, both known to influence dementia risk, also shape how much coffee people drink, and those factors cannot be fully disentangled in observational data.

Even so, the consistency of the findings across sexes, genetic backgrounds and more than four decades of follow-up strengthens the evidence base. With no curative treatment for dementia, and the available pharmaceutical options offering only modest benefit once symptoms appear, prevention has become the central focus of research. The 2024 update of the Lancet Commission on dementia concluded that up to 45 per cent of cases globally could be prevented or delayed by addressing modifiable risk factors.

On the current evidence, a daily habit a great many Australians already have may quietly belong on that list.

WT.24

Source Greek City Times