The Caffeine Cutoff: Why Your Third Cup of Coffee Matters More Than You Think

Drinking two to three cups of caffeinated coffee or one to two cups of tea daily is linked to a 15-20% lower risk of dementia, according to a large study following over 131,000 people for up to 43 years. The protective effect plateaus beyond this amount, suggesting there's an optimal sweet spot for brain health—and it's not about drinking as much as possible.

How Much Caffeine Actually Protects Your Brain?

Researchers tracked 131,821 participants in two long-running studies of medical professionals: the Nurses' Health Study for women and the Health Professionals Follow-up Study for men. Most were in their mid-40s or early 50s when the studies began. Over the decades, 11,033 participants developed dementia, documented through death certificates or physician diagnoses. The findings, published in JAMA, adjusted for numerous factors including health conditions, medications, diet, education, socioeconomic status, family history of dementia, body mass index (BMI), smoking, and mental illness.

The results were striking: people who drank between one and five 8-ounce cups of caffeinated coffee had about 20% less dementia risk compared with those who consumed virtually no caffeine. Those who drank at least one cup of caffeinated tea daily had about 15% less risk. But here's the catch—the benefit didn't increase beyond 2.5 cups of coffee daily. "This is a very large, rigorous study conducted long term among men and women that shows that drinking two or three cups of coffee per day is associated with reduced risk of dementia," said Aladdin Shadyab, an associate professor of public health and medicine at the University of California, San Diego.

Why Does Caffeine Help—But Decaf Doesn't?

The study found no protective benefit from decaffeinated coffee, suggesting caffeine itself is the active ingredient. Scientists believe caffeine works through several mechanisms:

• Neuroinflammation Reduction: Caffeine contains compounds that may reduce inflammation in the brain, a key driver of cognitive decline and dementia development.
• Vascular Function: Caffeine improves blood flow to the brain, ensuring neurons receive adequate oxygen and nutrients for optimal function.
• Insulin Sensitivity: Caffeine enhances how your body processes insulin, protecting against type 2 diabetes—a significant dementia risk factor.

The caffeine correlation held regardless of whether people had genetic risk factors for Alzheimer's disease or other dementias, suggesting the benefit isn't limited to those with specific genetic vulnerabilities.

What About Cognitive Decline Before Dementia?

The study also examined subjective cognitive decline—people's perception that their memory and thinking is slipping, often an early warning sign on the path toward dementia. Participants who drank more caffeine were less likely to report this subjective decline. Additionally, about 17,000 female participants older than 70 completed periodic cognitive tests. Those who consumed more caffeine had somewhat better scores for their age, suggesting their cognitive decline was slower by about seven months, according to Dr. Daniel Wang, the study's senior author and an epidemiologist specializing in neurodegenerative diseases at Mass General Brigham health system.

"If you can change your health habits early, before midlife, that will be more beneficial," Wang explained, noting that cognitive impairment develops over decades. This suggests that starting a moderate caffeine habit in your 40s or 50s may offer greater protection than beginning later in life.

The Milk and Sugar Problem

One important caveat emerged from related research: adding more than a little milk or sugar to your coffee may nullify caffeine's mortality benefits, according to Dr. Fang Fang Zhang, an epidemiologist at Tufts University's Friedman School of Nutrition Science and Policy. The dementia study itself didn't track milk or sugar consumption, so the impact on dementia risk specifically remains unclear. However, this finding suggests that how you prepare your coffee matters as much as how much you drink.

Some studies suggest that exceeding moderate amounts of caffeine can harm health by disrupting sleep or exacerbating anxiety, Zhang noted. Wang, who drinks about three cups each of coffee and green tea daily, said the study didn't find anything negative about larger caffeine quantities, but moderation appears to be the safest approach.

Who Should Start Drinking More Coffee?

For people who already drink coffee or tea regularly, the findings are reassuring. "It is reassuring to those who currently drink coffee that it may reduce risk of dementia," Shadyab said. However, for non-caffeine drinkers, the evidence doesn't necessarily mean you should overhaul your habits. "The findings don't necessarily suggest that we should be encouraging people to drink coffee, but non-caffeine drinkers might give it a try, starting with small amounts in case they are sensitive to caffeine," Zhang suggested.

One limitation: the study participants were medical professionals, which may not fully represent the general population. However, researchers noted that those who drank more caffeine were more likely to smoke and drink alcohol, suggesting they weren't exceptionally healthier than typical Americans. The correlation between caffeine and lower dementia risk was strongest for people younger than 75, reinforcing the importance of establishing healthy habits earlier in life.