Drinking several cups of coffee each day may lower the risk of depression, according to a new study.

The study, which was conducted by the Harvard School of Public Health in the US, found that increasing caffeine intake tended to reduce the risk of depression.

Women who drank the equivalent of two or three cups a day had a 15 percent lower risk of depression than non- or occasional-coffee drinkers. For heavy drinkers, drinking four or more cups of coffee a day, cut their risk by 20 percent.

The researchers said that the study doesn't prove that caffeine and caffeinated coffee reduces the risk of depression, but it suggests the possibility of a "protective effect". Their findings add weight to the work of others which found lower suicide rates among coffee drinkers. But they also said it is too soon to start recommending that women should drink more coffee to improve their mood.

The study looked at 50,000 healthy women, whose average age was 63. Over a ten-year period just over 2,600 participants developed depression.

Sweden is one of the world's biggest coffee drinking nations. Swedes consume an average of 8.2 kilograms of coffee per year, according to statistics from the World Research Institute.