Your Coffee Brewing Method Affects Cholesterol and Dementia Risk
Two to three cups of coffee a day is linked to an 18% lower risk of dementia.
But how that coffee gets made may matter just as much as how much of it gets drunk.
The Dementia Study Behind the Headlines
The finding comes from a study published in JAMA in February 2026, led by researchers at Mass General Brigham, the Harvard T.H. Chan School of Public Health, and the Broad Institute of MIT and Harvard.
Researchers tracked 131,821 participants from the Nurses' Health Study and Health Professionals Follow-Up Study for up to 43 years.
Of those participants, 11,033 developed dementia during the study period. Those with the highest intake of caffeinated coffee had an 18% lower risk of dementia compared with those who rarely or never drank it, according to Mass General Brigham's official summary of the findings.
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Why Decaf Didn't Show the Same Benefit
The protective effect was specific to caffeine, not coffee generally.
Decaffeinated coffee did not show the same association with reduced dementia risk in the study. Tea drinkers who consumed one to two cups daily saw comparable benefits to coffee drinkers, pointing to caffeine itself as the likely active factor.
Caffeinated coffee drinkers also reported lower rates of subjective cognitive decline — 7.8% compared with 9.5% among low or non-drinkers. Drinking more than three cups did not appear to add further protection, according to the Harvard Gazette's coverage of the study.
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The Brewing Method That Can Work Against You
A separate body of research complicates the simple "coffee is good for you" message.
Unfiltered coffee — cafetiere, also known as French press, along with Turkish and boiled coffee styles — contains far higher levels of compounds called diterpenes than filtered coffee.
The two main diterpenes, cafestol and kahweol, are oils released from coffee grounds during steeping. Paper filters trap most of these oils before they reach the cup; metal mesh filters, like those used in a French press, do not. Research published in the cardiology journal Open Heart found that drinking six or more cups of unfiltered coffee daily can meaningfully raise LDL cholesterol. Switching to a paper filter, or limiting unfiltered cups, is the simplest way to avoid the effect.
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What's Happening at the Cellular Level
A separate King's College London study, published in November 2025 in BMJ Mental Health, looked at coffee's effect on telomeres — the protective caps at the ends of chromosomes that shorten with age.
The study followed 436 adults with schizophrenia, bipolar disorder, or psychotic depression. Those drinking three to four cups of coffee daily had telomere lengths comparable to a biological age roughly five years younger than non-coffee drinkers, according to lead researcher Vid Mlakar.
The effect reversed at higher intake — participants drinking more than four cups a day had shorter telomeres than those drinking three to four. The study's authors noted the findings apply specifically to a population already at elevated risk of accelerated biological aging, not the general public.
What the Science Adds Up To
Coffee also appears to influence the gut microbiome in ways researchers are still working to fully understand.
ZOE's PREDICT studies, led by Prof. Tim Spector, found that coffee drinkers tend to have greater microbiome diversity, likely linked to coffee's soluble fibre and prebiotic properties.
Separate observational research suggests three to five cups of black coffee daily may reduce type 2 diabetes risk by up to 30% over the long term — though caffeine on an empty stomach or after poor sleep can raise blood sugar in some people. None of these findings change the core picture: moderate, filtered, caffeinated coffee is where the consistent evidence sits — and the cup count that matters most is the one that stays within three to four.
Key Takeaways
- A JAMA study of 131,821 people found 2–3 cups of caffeinated coffee daily was linked to an 18% lower dementia risk.
- Decaffeinated coffee showed no comparable benefit — caffeine appears to be the active protective factor.
- Unfiltered coffee (French press, Turkish, boiled) contains far more cholesterol-raising diterpenes than paper-filtered coffee.
- A King's College London study of 436 people found 3–4 cups daily linked to telomere lengths equivalent to a 5-year younger biological age — though the study population had severe mental illness, not the general public.
- Benefits from coffee plateau or reverse above 4 cups a day across multiple studies.
- ZOE's PREDICT research found coffee drinkers have greater gut microbiome diversity, linked to coffee's fibre and prebiotic content.
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Health & Science Correspondent
Dr. Chris Farley brings a medical background to his reporting on healthcare policy, scientific research, and global health developments. He makes complex medical news easy to understand.
