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Being physically active can help reduce the risk of womb cancer

by Ed Yong | Analysis

29 September 2010

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Physical activity could help to reduce the risk of womb cancer

Physical activity could help to reduce the risk of womb cancer

Keeping active is great for your health. It keeps excess fat at bay, gives you a rush of mood-enhancing endorphins, and keeps your bones and muscles strong. Many studies have also shown that keeping physically active can reduce the risk of bowel and breast cancers.

But a new study has just been published in the British Journal of Cancer, which confirms that being active also reduces the risk of womb cancer (technically, “endometrial” cancer, which starts in the lining of the womb).

To investigate the link, the researchers looked at the combined results of many different studies into activity and womb cancer risk. This gave them an overall, more reliable, picture of the effects of physical activity.

And that wasn’t all: these overall results also hinted that spending too long sitting down was also linked to a higher risk of womb cancer.

‘Probable’ link strengthened

Back in 2007, three studies reviewed all the existing evidence on physical activity and womb cancer, all concluding that being active ‘probably’ reduced the risk of this type of cancer.

At that time, the evidence wasn’t strong enough to conclude that there was a definite link. This was because only a few studies had enrolled healthy people at the start and followed them up over time. These “prospective studies” are less prone to bias than ones which recruit people with and without the disease, and ask them to remember their previous habits.

But since then, five such studies, looking at this link, have been published. These include extremely large studies like the EPIC study, which Cancer Research UK helps to fund.

Adding the latest sets of results gave more weight to the conclusions, and the researchers are now confident that the link they’ve found isn’t just down to chance. Active women, they found, had about a 30 per cent lower risk of womb cancer than inactive women.

How could activity be affecting womb cancer risk?

The lining of the womb grows thicker and then breaks down throughout the month, as the levels of hormones in women’s bodies change. This is a normal part of the menstrual cycle, but it can be affected by shifts in hormone levels that aren’t related to the normal cycle. For example, taking HRT increases the levels of oestrogen in the body, causing the womb lining to grow more and increasing the risk of cancer.

But being physically active lowers the oestrogen levels in your blood. And it also simultaneously raises levels of another protein, called SHBG, which clamps onto oestrogen and stops it working. This prevents oestrogen from making cells divide too much.

Being physically active also helps to prevent weight gain, keeping away extra fat cells which are constantly pumping out hormones including oestrogen. That’s why being overweight increases the risk of womb cancer – in fact, it’s estimated that about a third of cases in the UK are linked to being overweight or obese.

Being active also reduces the levels of the hormone insulin in the body. This is important because insulin, and other chemicals that depend on it, can make womb cells grow and divide, again increasing the risk of cancerous changes.

Are you sitting comfortably?

Three of the studies that were included in the analysis also looked separately at the amount of time people spent sitting during the day. They found that the people who sat the longest had between 40 per cent and 80 per cent higher risks of womb cancer compared with those who were sitting down for the shortest times.

Taking into account the amount of exercise the women were doing, the researchers found that women who spent the most time sitting down had a higher womb cancer risk. Women who were inactive and sat down for more than 9 hours a day had over twice the risk of the disease of active women sitting down for less than 3 hours a day.

All in all, these results give an indication that sitting down could independently affect womb cancer risk, but the evidence isn’t as much or as strong as that for physical activity.

Reducing the risk

The authors of the latest study estimated that if everyone was active for more than 20 minutes, five times a week, 22% of womb cancers could be prevented. That’s over 1,600 cases every year. This estimate is likely to be on the high side, since they used the study which showed the biggest effect to calculate the estimate.

But it’s still a good idea to be physically active. Not only can it reduce the risk of womb cancer, but also bowel and breast cancers, and many other chronic diseases.

Other elements of our lifestyle can also affect our womb cancer risk. Keeping a healthy weight is important, because fat is active and pumps out hormones and chemicals that make cells divide.

And things that affect hormone levels in the body can also affect the risk. Having children reduces the risk of the disease, as does taking the combined contraceptive Pill, whereas some types of HRT that only contain oestrogen increase the risk.

Womb cancer rates have been going up for the last 30 years, so it’s important to find out why, so we can find out how to slow this rise. And this study’s shown that keeping active could well have an important part to play in preventing the disease.