Moderate coffee and tea consumption linked to lower risk of dementia

A new analysis of long-term dietary habits suggests that your daily cup of coffee or tea might do more than just provide a morning jolt. Researchers have determined that moderate consumption of caffeinated beverages is linked to a lower risk of dementia and better physical brain function over time. These results were published in the journal JAMA.

Dementia and Alzheimer’s disease represent a growing health challenge as the global population ages. Current medical treatments offer limited benefits once symptoms appear, and they cannot reverse the condition. This reality has prompted medical experts to look for lifestyle habits that might delay the onset of cognitive decline. Diet is a primary area of focus because it is a factor that individuals can control in their daily lives.

Coffee and tea are of particular interest to nutritional scientists. These beverages contain chemical compounds that may protect brain cells from damage. These include caffeine and polyphenols, which are plant-based micronutrients with antioxidant properties.

Prior attempts to measure this potential benefit have yielded mixed results. Some earlier inquiries relied on participants remembering their dietary habits from the distant past. Others checked in with participants only once, failing to capture how habits change over a lifetime. To address these limitations, a team led by Yu Zhang and Daniel Wang from the Harvard T.H. Chan School of Public Health and Mass General Brigham undertook a more expansive approach.

The investigators analyzed data from two massive, long-running groups of medical professionals. The study included over 130,000 female nurses and male health professionals who provided updates on their health and diet for up to forty-three years. Unlike smaller snapshots of time, this project tracked dietary habits repeatedly. Participants filled out detailed questionnaires about what they ate and drank every two to four years.

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This distinct method allowed the researchers to reduce errors associated with memory. It also helped them calculate a cumulative average of caffeine intake over decades. The team looked for associations between these drinking habits and three specific outcomes: the clinical diagnosis of dementia, self-reported memory problems, and performance on objective cognitive tests.

The data revealed a distinct pattern regarding the consumption of caffeinated beverages. Individuals who drank caffeinated coffee had a lower chance of developing dementia compared to those who avoided it. The relationship followed a specific curve rather than a straight line.

The greatest reduction in risk appeared among people who drank approximately two to three cups of caffeinated coffee per day. Consuming more than this amount did not result in additional benefits, but it also did not appear to cause harm. This finding contradicts some earlier fears that high caffeine intake might be detrimental to the aging brain.

Tea drinkers saw similar benefits. Consuming one to two cups of tea daily was linked to a lower likelihood of dementia diagnosis. In contrast, the researchers found that the results were not statistically significant among those who drank decaffeinated coffee. This distinction suggests that caffeine itself may play a central role in the observed neuroprotection.

The study also looked at how well participants could think and remember as they aged. In a subset of the participants who underwent telephone-based testing, higher caffeinated coffee intake tracked with better scores on performance tasks. These tests measured verbal memory, attention, and executive function.

The difference in scores was roughly equivalent to being several months younger in terms of brain aging. Even among people who carried genes that usually increase the risk of Alzheimer’s, the link between caffeine and better brain health remained consistent. The researchers also assessed “subjective cognitive decline.” This is a stage where individuals feel they are having memory slips before a doctor can detect them. Higher caffeine intake was associated with fewer reports of these subjective problems.

These results add weight to a growing body of evidence linking caffeine to neurological health. However, the findings do not perfectly align with every previous study. For example, recent analyses of the UK Biobank database also found that coffee drinkers had a lower risk of neurodegenerative conditions. That research highlighted that unsweetened coffee seemed most beneficial.

The UK Biobank findings differed slightly regarding decaffeinated coffee. While the Harvard team found no link between decaf and dementia risk, the UK study suggested decaf might still offer some protection. This discrepancy implies that other compounds in coffee besides caffeine might play a role, or that different populations metabolize these beverages differently.

Other research utilizing brain imaging has offered clues about why this might happen. A study from the Australian Imaging, Biomarkers and Lifestyle study of aging found that higher coffee consumption was associated with a slower buildup of amyloid proteins in the brain. These proteins are the sticky clumps associated with Alzheimer’s disease.

The new Harvard study aligns with the theory that caffeine helps maintain neural networks. It supports the idea that moderate stimulation of the brain’s chemical receptors might reduce inflammation. Caffeine blocks specific receptors in the brain known as adenosine receptors. When these receptors are blocked, it affects the release of neurotransmitters and may reduce the stress on brain cells.

Researchers have also observed in animal models that caffeine can suppress the enzymes that create amyloid plaques. It appears to enhance the function of mitochondria, which are the power plants of the cell. By improving how brain cells use energy, caffeine might help them survive longer in the face of aging.

Additional context comes from the National Health and Nutrition Examination Survey in the United States. That separate analysis found that older adults who consumed more caffeine performed better on tests of processing speed and attention. The consistency of these findings across different populations strengthens the argument that caffeine has a measurable effect on cognition.

Despite the large sample size of the new Harvard analysis, the study has limitations inherent to observational research. It demonstrates an association but cannot definitively prove that coffee causes the reduction in dementia cases. It is possible that people who start to experience subtle cognitive decline naturally stop drinking coffee before they are diagnosed. This phenomenon is often called reverse causation.

The researchers attempted to account for this by conducting sensitivity analyses. They looked at the data in ways that excluded the years immediately preceding a diagnosis. The protective link remained, suggesting that reverse causation does not fully explain the results.

The participants in this study were primarily white medical professionals. This fact means the results might not apply perfectly to the general population or to other racial and ethnic groups. Additionally, the questionnaires did not distinguish between different preparation methods. The study could not separate the effects of espresso versus drip coffee, or green tea versus black tea.

Unmeasured factors could also be at play. Coffee drinkers might share other lifestyle habits that protect the brain, such as higher levels of social activity or different dietary patterns. The researchers used statistical models to adjust for smoking, exercise, and overall diet quality. However, observational studies can never fully eliminate the possibility of residual confounding variables.

Future science needs to clarify the biological mechanisms at play. Researchers must determine if caffeine is acting alone or in concert with other antioxidants found in these plants. Clinical trials that assign specific amounts of caffeine to participants could help confirm these observational findings.

The senior author of the study, Daniel Wang, noted the perspective needed when interpreting these results. “While our results are encouraging, it’s important to remember that the effect size is small and there are lots of important ways to protect cognitive function as we age,” Wang said. “Our study suggests that caffeinated coffee or tea consumption can be one piece of that puzzle.”

For now, the data suggests that a moderate coffee or tea habit is a generally healthy choice for the aging brain. It appears that consumption of about three cups of coffee or two cups of tea provides the maximum potential benefit. This study provides reassurance that this common daily ritual does not harm cognitive function and may help preserve it.

The study, “Coffee and Tea Intake, Dementia Risk, and Cognitive Function,” was authored by Yu Zhang, Yuxi Liu, Yanping Li, Yuhan Li, Xiao Gu, Jae H. Kang, A. Heather Eliassen, Molin Wang, Eric B. Rimm, Walter C. Willett, Frank B. Hu, Meir J. Stampfer, and Dong D. Wang.