Coffee linked to lower risk of endometrial cancer

By Lilian Anekwe

BMJ Group News

What do we know already?

Endometrial cancer starts in the endometrium, the lining of the uterus (womb). Some of the things that make a woman more likely to get endometrial cancer, called risk factors, include being overweight, having diabetes, or having previous menstrual or fertility problems.

A few studies have suggested that the more coffee a woman drinks, the lower her risk of endometrial cancer. But these haven’t always been good-quality studies and it’s been difficult to know if the effects on endometrial cancer are due to coffee itself, or to caffeine.

To try and find out more about the relationship between coffee and endometrial cancer, researchers studied a large group of women who took part in a study, called the Nurse’s Health Study. They asked 67,470 women who were aged between 34 and 59 in 1980 how many cups of coffee they drank in a day. They also recorded how many women in the study got endometrial cancer between 1980 and 2006. From this they were able to calculate the link between how likely women were to get endometrial cancer depending on how much coffee they drank.

What does the new study say?

Drinking fewer than four cups a day had no effect on endometrial cancer. However, women who drank more than four cups of coffee a day had a 25 percent lower risk of endometrial cancer than women who drank less than one cup per day.

When researchers looked at the type of coffee, they found that women who drank more than four cups of caffeinated coffee a day had 30 percent lower risk of endometrial cancer compared with those who drank less than one cup a day.

Women who drank two cups or more of decaffeinated coffee a day had a 22 percent lower risk of endometrial cancer compared with those who had less than one cup a day, but this effect was not more than could be expected purely by chance.

There was no relationship between the amount of tea consumed and a woman’s risk of endometrial cancer.

The authors suggest that caffeinated coffee may contain substances that prevent endometrial cancer from developing, or prevent other chemicals that cause endometrial cancer from doing any damage.

How reliable is the research?

This kind of study, that asks for information about people’s health and lifestyle then records how many then go on to get a disease, is usually a reliable way to see if there’s a relationship between two things. But it can’t tell us if drinking coffee stops women from getting endometrial cancer, only that there’s a link between the two things.

The researchers accounted for many of the risk factors for endometrial cancer - women’s age and weight, whether they had children, if they had taken the pill or other hormones, how much they smoked and drank and if they had other illnesses or cancers. They also asked lots of general questions about women’s diet and accounted for these.

But some groups within the study were very small. For example there were relatively few women in the study who hadn’t yet gone through the menopause, and less than two percent of the women in the study actually drank more than four cups of decaffeinated coffee a day. When conclusions are based on small numbers of people we can be less confident that they are genuine.