Drinking tea linked to prostate cancer - but study is flawed
Men who drink many cups of tea a day are more likely to get prostate cancer, compared to men who only drink a few cups of tea a day. But although this new study sounds alarming, there are problems which mean we can't be sure how strong the link is.
BMJ Group News
What do we know already?
Prostate cancer is the most common cancer among men in the UK, and has become more common over the last 30 years. So there's a lot of research to try and find out why prostate cancer is becoming more common.
There have been some studies that have looked at whether different types of tea might affect how likely men are to get prostate cancer.
To find out more, researchers looked at a group of more than 6,000 Scottish men who took part in a study in the early seventies. The men filled out questionnaires about different aspects of their lifestyle, including how much tea they drank each day. They were divided into men who drank three or fewer cups a day, those who drank four or five, those who drank six, and those who drank seven or more cups a day.
The researchers then recorded how many men got prostate cancer over the following 37 years. From this they were able to calculate whether tea drinking was linked to an increased risk of prostate cancer.
What does the new study say?
During the study, 318 men got prostate cancer. The link between drinking tea and prostate cancer was strongest in men who drank more than seven cups of tea a day. These men had a 50 percent higher risk of getting prostate cancer than men who drank less than three cups of tea a day.
There was no link between how many cups of tea men drank and how advanced their cancer was. But the researchers didn't have information from all of the men about how advanced their cancer was.
How reliable is the research?
This is a study of a large group of men that recorded how many got prostate cancer over many years.
But there are lots of problems with this study that make the results less reliable.
- This study looked at the link between drinking tea and being more likely to get prostate cancer. It did not look at how many men died from prostate cancer, and whether more men who drank lots of tea died from prostate cancer than those who drank less tea. But we know that most prostate cancers grow slowly, and many men live for years without getting any symptoms. More than 7 out of 10 men will still be alive five years after being diagnosed.
- The researchers didn't have information from all of the men about the type of tea they drank, although they do say most men drank black tea. But we can't be certain that the risk is the same for all types of tea.
- The researchers didn't collect information about whether the men in the study had a close male relative who had prostate cancer. So the researchers were not able to take this into account in their calculations. We know family history can increase your chances of getting prostate cancer.
- The men in the study only filled in questionnaires about their lifestyle once at the beginning of study. The study lasted 37 years, during which time it's likely their lifestyles changed, but we can't be sure if this affected the results.
- The researchers noted that men who drank the most tea also had a relatively healthy lifestyle. More men who drank seven or more cups of tea a day had a healthy weight, didn't drink any alcohol, and had healthy amounts of cholesterol in their blood. So it may have been that these men lived for longer than others. Prostate cancer becomes more common the older men are.
- Although this was a large study, the numbers of men who had prostate cancer were small. Some 318 men had prostate cancer and only 92 men drank seven or more cups of tea a day.