Is Coffee Good for Your Brain? What a 43-Year Study Found

Coffee is one of the most-searched health questions there is. A big study published in JAMA in February 2026 gave a clearer answer for the brain, and it's been making the rounds again this month.

What the study found

Promising evidence

Researchers from Mass General Brigham and the Harvard T.H. Chan School of Public Health followed 131,821 people (nurses and other health professionals) for up to 43 years, with repeated food questionnaires and cognitive check-ins. Over that time, 11,033 developed dementia.

• People who drank the most caffeinated coffee had about an 18% lower dementia risk than people who drank little or none.
• The strongest link was at 2 to 3 cups a day. More than that added no extra benefit.
• Caffeinated tea (1 to 2 cups a day) showed a similar pattern.
• The link held for people with high and low genetic risk.

The twist: decaf

Decaf coffee did not show the link. That hints that caffeine may be part of the story, though the study can't prove it.

The honest part

This is an observational study. It shows a link, not proof. Coffee drinkers may differ from non-drinkers in other ways. The senior author described the effect size as small. Coffee is one small piece of brain health, next to sleep, movement, blood pressure and staying social.

How we actually do it

• 2 to 3 cups, done by about 2 p.m. In a small sleep-lab study, 400 mg of caffeine (about 4 cups) taken even 6 hours before bed cut sleep by about an hour. Early evidence
• Skip the sugary syrups. A splash of milk or a pinch of cinnamon keeps it tasty without the added sugar. The American Heart Association suggests keeping added sugar to about 25 g a day for women and 36 g for men.
• Know your number. The FDA says up to 400 mg a day isn't generally linked to harm in healthy adults.

Who should check first

If you're pregnant, keep caffeine under 200 mg a day (ACOG). If you have heart rhythm issues, anxiety, reflux or trouble sleeping, talk to your doctor about what's right for you.

One thing this week

Note what time your last cup is each day. If it's after 2 p.m., move it earlier for a week and see how you sleep.

Sources

1. Zhang Y, Wang DD, et al. Coffee and Tea Intake, Dementia Risk, and Cognitive Function. JAMA, 2026. doi:10.1001/jama.2025.27259 Link
2. Mass General Brigham news release, Feb 9 2026 (EurekAlert) Link
3. Drake C, et al. Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed. J Clin Sleep Med. 2013;9(11):1195-1200. Link
4. FDA. Spilling the Beans: How Much Caffeine Is Too Much? Link
5. ACOG. Moderate Caffeine Consumption During Pregnancy. Link