Here's the short version of the findings:

Caffeinated coffee was linked to lower dementia risk. Comparing the highest vs lowest consumption groups, the study reported a hazard ratio of 0.82 (95% CI, 0.76 to 0.89), which means higher caffeinated coffee intake was associated with lower risk.

People also reported less subjective cognitive decline. The higher-intake group had 7.8% prevalence vs 9.5% in the lower-intake group (prevalence ratio 0.85).

The "sweet spot" looked moderate. The most pronounced differences showed up around 2 to 3 cups per day of caffeinated coffee.

Decaf did not show a significant association with dementia risk.

The long-running study, led by researchers from Mass General Brigham, Harvard T.H. Chan School of Public Health, and the Broad Institute of MIT, tracked 131,821 U.S. adults for four decades and documented 11,033 dementia cases. One major finding was a very clear pattern: adults who drank about three cups of coffee per day, or one to two cups of tea, had a much lower risk of dementia and more favorable cognitive outcomes over their lifetimes. Decaf, however, did not show the same relationship.

Both male and female participants who drank more than three cups of caffeinated coffee per day had an 18% lower risk of dementia compared with those who reported little or no daily caffeinated coffee consumption.

"When searching for possible dementia prevention tools, we thought something as prevalent as coffee may be a promising dietary intervention - and our unique access to high-quality data through studies that have been going on for more than 40 years allowed us to follow through on that idea," said senior author Daniel Wang, associate scientist with the Channing Division of Network Medicine in the Mass General Brigham Department of Medicine and assistant professor at Harvard Medical School.

Wang noted, "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. Our study suggests that caffeinated coffee or tea consumption can be one piece of that puzzle."

The cognitive upside of caffeinated coffee is clear.

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