Coffee and tea: a large study reveals their impact on the risk of dementia

A Comprehensive Analysis of Caffeine Consumption

A new prospective cohort study, conducted by researchers at Mass General Brigham, the Harvard T.H. Chan School of Public Health, and the Broad Institute of MIT and Harvard, sheds new light on our morning habits. The researchers analyzed data from 131,821 participants in two major studies: the Nurses’ Health Study (NHS) and the Health Professionals Follow-Up Study (HPFS).

The results of this study, published in the medical journal JAMA, highlight a significant link between the consumption of caffeinated beverages and brain health. According to this analysis, moderate consumption of caffeinated coffee—two to three cups per day—or tea—one to two cups per day—is associated with a reduced risk of dementia.

Beyond simply reducing risk, the study also suggests that these habits may slow cognitive decline and help preserve overall cognitive function. Daniel Wang, MD, ScD, lead author, a research scientist in the Channing Division of Network Medicine at the Department of Medicine at Mass General Brigham and an assistant professor at Harvard Medical School, explains the origins of this research: “As we were looking for potential tools to prevent dementia, we thought that something as widespread as coffee might be a promising dietary intervention—and our unique access to high-quality data from studies that have been ongoing for more than 40 years allowed us to bring this idea to life.”

Why Prevention Has Become the Priority

The emphasis on early prevention is particularly crucial in the field of dementia. Indeed, current treatments remain limited and generally offer only modest benefits once the symptoms of the disease have appeared. Given this reality, research has turned to studying the influence of lifestyle factors—such as diet—on the development of dementia.

Scientists are particularly interested in the chemical composition of our daily beverages. Coffee and tea contain bioactive compounds, including polyphenols and caffeine. These compounds have emerged as potential neuroprotective factors capable of reducing inflammation and cellular damage.

By influencing these biological mechanisms, these substances may play a protective role against cognitive decline. Daniel Wang, who is also an assistant professor in the Department of Nutrition at the Harvard Chan School and an associate member at the Broad Institute, however, qualifies the significance of these findings: “Although our results are encouraging, it’s important to remember that the effect size is small and that there are many important ways to protect cognitive function as we age. Our study suggests that drinking coffee or caffeinated tea may be one piece of that puzzle.”

What Sets This Study Apart from Previous Ones

Although promising, previous findings regarding the relationship between coffee and dementia had been inconsistent. Earlier studies often had limited follow-up periods and lacked sufficient detail to capture long-term consumption patterns, differences by beverage type, or the full continuum of clinical outcomes.

Data from the NHS and the HPFS helped overcome these methodological challenges. Participants underwent repeated assessments of their diet, dementia, subjective cognitive decline, and objective cognitive function. These individuals were followed for up to 43 years, providing a rare temporal perspective in medical research.

This depth of analysis allowed researchers to precisely compare how caffeinated coffee, tea, and decaffeinated coffee influenced each participant’s risk of dementia and cognitive health. The study thus covers the entire spectrum, from early subjective cognitive decline to clinically diagnosed dementia.

Key figures: 18% lower risk

The study’s large scale provides robust statistics. Of the more than 130,000 participants followed, 11,033 developed dementia. The analyses revealed that participants—men and women combined—with the highest intake of caffeinated coffee had an 18% lower risk of dementia compared to those who consumed little or no caffeinated coffee.

Caffeinated coffee drinkers also showed a lower prevalence of subjective cognitive decline, with a rate of 7.8% compared to 9.5% for the others. According to certain measurements taken during the study, those who drank caffeinated coffee also performed better on objective tests of overall cognitive function.

A key finding of the study concerns the nature of the beverage. Higher tea consumption yielded results similar to those of coffee. In contrast, decaffeinated coffee did not produce the same effects. This suggests that caffeine may be the active factor responsible for these neuroprotective effects, although further research is needed to confirm the responsible factors and the exact mechanisms.

Optimal Dosage and Genetic Factors

The study identified an optimal consumption window. Cognitive benefits were most pronounced among participants who consumed two to three cups of caffeinated coffee or one to two cups of tea per day. Contrary to several previous studies, higher caffeine intake did not result in negative effects; on the contrary, it provided neuroprotective benefits similar to those observed with the optimal dose.

The researchers also examined the influence of genetics. Yu Zhang, MBBS, MS, lead author, a doctoral student at the Harvard Chan School and a research fellow at Mass General Brigham, elaborates on this aspect of the study: “We also compared people with different genetic predispositions to developing dementia and found the same results—which means that coffee or caffeine is likely just as beneficial for people with both high and low genetic risk of developing dementia.”

This finding suggests that the potential benefits of these beverages are accessible regardless of an individual’s genetic profile, offering a universal approach within the context of lifestyle-based prevention strategies.

Source: medicalxpress.com

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Coffee and tea: a large study reveals their impact on the risk of dementia