Consuming high amounts of caffeine appears to protect women from developing dementia or cognitive impairment, according to the results of a new study published in The Journals of Gerontology, Series A: Biological Sciences and Medical Sciences. Researchers, however, aren’t sure why.

Specifically, daily consumption of an amount of caffeine equal to that found in two to three eight-ounce cups of coffee, five to six eight-ounce cups of black tea, or seven to eight 12-ounce cans of cola (261 mg) was associated with a 36% reduction in the risk of dementia over 10 years.

“The mounting evidence of caffeine consumption as a potentially protective factor against cognitive impairment is exciting given that caffeine is also an easily modifiable dietary factor with very few contraindications,” said Ira Driscoll, Ph.D., the study’s lead author and a professor of psychology at the University of Wisconsin–Milwaukee.

Driscoll and colleagues used data from the Women’s Health Initiative Memory Study, specifically looking at 6,467 community-dwelling postmenopausal women aged 65 or more years. The researchers estimated caffeine intake from questions about coffee, tea and cola beverage consumption, including frequency and serving size.

The women’s cognitive function was assessed annually in 10 or fewer years of follow-up; 388 of them received a diagnosis of probable dementia or some form of global cognitive impairment. Dementia or impairment was diagnosed at a lower rate in those who had consumed more than the median amount of caffeine for the group studied (with an average intake of 261 mg per day) compared with those whose intake was below the median (with an average intake of 64 mg per day).

The researchers adjusted for risk factors such as hormone therapy, age, race, education, body mass index, sleep quality, depression, hypertension, prior cardiovascular disease, diabetes, smoking and alcohol consumption.

Future research is needed to help clarify the relationship between caffeine and cognitive health, Driscoll said.