Drinking more than three cups of coffee a day helped protect older women against some age-related memory decline, according to French researchers, giving women more reason to love the world's most popular stimulant.

Men did not enjoy the same benefit, they said.

"The more coffee one drank, the better the effects seemed to be on (women's) memory functioning in particular," said Karen Ritchie at the French National Institute of Medical Research, whose work appears in the journal Neurology.

The researchers followed more than 7,000 men and women in three French cities, checking their health and mental function and asking them about their current and past eating and drinking habits, their friends, and their daily activities.

They used this information to sort out the specific role caffeine played in these women's lives.

They found that women who drank more than three cups of coffee per day, or its caffeine equivalent in tea, retained more of their verbal and -- to a lesser extent -- visual memories over four years.

These women had a 33 per cent lower odds of having verbal memory declines and 18 per cent lower odds of having visual and spatial memory declines, compared to women who drank one cup or fewer per day.

The effect also depended on age, with women over 80 reaping more benefits from these beverages than those who were 10 to 15 years younger, Ritchie's team wrote.

It was unclear whether current or former coffee consumption made the difference.

Some studies in mice have suggested that caffeine might block the buildup of proteins that lead to mental decline.

Ritchie is not sure why only women benefited in her study.

"Our best guess is that women don't metabolize coffee in the same way (as men)," she said in a telephone interview.

Ritchie plans to follow the women longer to see if caffeine delays the onset of dementia -- the mental confusion that signals Alzheimer's disease and other brain disorders.

She said people should weigh any brain gains derived from caffeine against other effects of the stimulant, including raised blood pressure.

The average American drinks one to two cups of coffee a day, according to the National Coffee Association.