Women who consume high amounts of caffeine may have a reduced risk of developing dementia, a new study suggests.

US researchers looked at almost 6,500 postmenopausal women aged 65 and older, all of whom consumed caffeine in varying amounts.

The women were monitored over a 10-year period and during that time, almost 400 were diagnosed with probable dementia or some form of cognitive impairment.

The study found that those who consumed more than 261mg of caffeine per day had a 36% reduced risk of developing dementia compared to those who consumed lower amounts. That amount is equivalent to two or three 8-oz cups of coffee per day, five or six 8-oz cups of black tea, or seven or eight 12-oz cans of cola (slightly bigger than a standard 330ml can in Ireland).

The researchers took into account other factors that could have affected the results, such as age, body mass index, high blood pressure, smoking, prior heart disease and alcohol consumption.

"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," commented the study's lead author, Dr Ira Driscoll, of the University of Wisconsin-Milwaukee.

Details of these findings are published in The Journals of Gerontology, Series A: Biological Sciences and Medical Sciences.