Does weight affect a woman's cancer risk?
Publication Date:08/11/2007
Being overweight or obese increases a woman's chance of getting cancer of the womb almost threefold and also raises the risk of breast cancer, according to a new study.
What do we know already?
We know that being overweight or obese may increase the risk of cancer. A recent report from the World Cancer Research Fund said that, apart from not smoking, staying at a healthy weight was the most important thing we can do to prevent cancer.
Now researchers have looked at the links between weight and 17 cancers, in a big study of more than a million women aged 50 to 64, to see how strong the links are, and how much difference a woman's weight makes before and after the menopause.
The researchers used definitions of weight based on your body mass index, or BMI. You can calculate your BMI by dividing your weight in kilograms by your height in metres squared. A BMI of 25 or over is classed as overweight, and 30 or over is classed as obese.
What does the new study say?
The researchers found links between being overweight or obese for some cancers, but not all of them.
The most common cancers with a strong link to being overweight or obese were endometrial cancer and breast cancer. Women were almost three times as likely to get endometrial cancer if they were overweight or obese. They were 40 percent more likely to get breast cancer if they were overweight or obese (but only after the menopause).
Other cancers were also strongly linked to being overweight or obese, but they are less common: one type of throat cancer (called adenocarcinoma of the oesophagus), pancreatic cancer, kidney cancer and leukaemia.
These cancers are linked to being overweight or obese, but the link is not as strong: ovarian cancer, non-Hodgkins lymphoma, multiple myeloma.
In all these cancers, the risk increased in line with the women's weight. The higher the weight, the higher the risk of cancer.
It makes a difference whether you have gone through the menopause or not. Being overweight or obese is only a risk for breast cancer in women who've been through the menopause. It doesn't increase your risk of getting breast cancer before the menopause.
Tell me more about the study's findings
The strongest link between cancer and being overweight that the researchers found was for endometrial cancer. The researchers estimate that half of endometrial cancers in women who've been through the menopause are caused by being overweight or obese.
Other links were less strong. For example, the researchers think that only 7 in 100 cases of breast cancer in women who'd been through the menopause were caused by being overweight or obese. Other things, like your genes and how many children you've had, may have more effect on your risk.
Being overweight also seems to increase a woman's risk of getting bowel cancer before the menopause, but not afterwards. We don't know why this is.
Where does the study come from?
The study was carried out by researchers at the Cancer Epidemiology Unit at the University of Oxford, UK. It was published in the BMJ (British Medical Journal).
How reliable are the findings?
This was a very big study. The researchers followed 1.2 million women in the UK, aged 50 to 64, for about 7 years. They recorded a lot of information about the women, including their weight, whether they smoked, how many children they had, their background and whether they'd used hormone replacement therapy (HRT). They looked at how many women got cancer or died from cancer during the study. Then they looked to see what effect their weight had on their likelihood of getting cancer, after taking account of all the other things that could have made a difference.
The size of the study, and the amount of information collected, means that the results are quite reliable.
What does this mean for me?
If you are a woman aged 50 or over, and you are overweight or obese, these results show that your risk of some types of cancer is higher than it would be if you were a healthy weight.
The researchers estimate that about 5 in 100 cancers each year in the UK could be avoided if people stayed a healthy weight. That's 6,000 cancers a year. But weight is not the only thing that affects your risk of cancer. There are no ways to guarantee that you won't get cancer. All you can do is decide how much you want to try to reduce your risk.
What should I do now?
If you smoke, stopping smoking is the most important thing you can do to cut down your risk of cancer. If you don't smoke, keeping to a healthy weight can reduce your risk of some types of cancer. The best way to keep a healthy weight is to eat a balanced diet with plenty of fruit and vegetables, and to take regular exercise.
If you need advice about diet and exercise, your doctor should be able to help.
From:
Reeves GK, Pirie K, Beral V, et al. Cancer incidence and mortality in relation to body mass index in the Million Women Study: cohort study. BMJ. Published online 6 November 2007.
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© BMJ Publishing Group Limited ("BMJ Group") 2007. All rights reserved
This information does not replace medical advice. If you are concerned you might have a medical problem please ask your Boots pharmacy team in your local Boots store, or see your doctor.
