Some scary figures were released last week: the number of women with breast cancer has risen by 81 per cent in the past 33 years. Although breast cancer death rates are also falling, the statistics are deeply worrying for women, not least because scientists says that it’s hard to pin down the exact cause of the rise.
However, a more hopeful message will emerge at the National Cancer Research Institute Conference in Birmingham next week. The conference will hear that there is something women can do to reduce the risk of breast cancer: exercise. The message will be made in a keynote speech supported by the charity Breakthrough Breast Cancer, and will mark a new era in official acknowledgement from cancer research bodies that there is a clear link between activity and a reduction in breast cancer.
Professor Leslie Bernstein, the chair in cancer research at the University of California, will draw on 20 years’ research into the effect of exercise on breast cancer rates and will conclude that young girls can significantly reduce their risk of developing breast cancer as they get older if they exercise regularly in their teens. And both pre-menopausal and post-menopausal adults can improve their odds of staying clear of the disease by keeping active.
Her research indicates that exercising over a lifetime seems to have the strongest protective effect; young women who exercise for just four hours a week over their entire reproductive years experience more than a 50 per cent reduction in breast cancer risk. But exercising in adolescence may be particularly crucial; another of her studies showed that breast cancer risk was reduced by 30 per cent among women who exercised for two hours or more every week during their teens. It all gives extra cause for concern over Britain’s couch-potato youth.
The results of Professor Bernstein’s latest research, until now unreported in the UK, may be even more significant. In a 35-year study of 133,000 women, called the California Teachers Study, new data indicates that physical activity may have a special importance in preventing a type of breast cancer called oestrogen-receptor negative (ORN) breast cancer, with women who exercise five times or more a week experiencing a 50 per cent reduction in risk of these types of tumour. This is important because ORN breast cancers tend to be harder to prevent recurring.
In women who have already had the other main kind of breast cancer, oestrogen-receptor positive (ORP), hormone treatments such as tamoxifen can protect against recurrence. This doesn’t work with ORN tumours, so exercise is potentially one of the best preventive measures in a doctor’s armoury.
For many years, the main risk factors for breast cancer have been accepted as gender, family history, early periods, late menopause, not having children and — most importantly — age. That still applies, says Professor Alan Ashworth, the director of the Breakthrough Research Centre. But there is little that women can do about any of these. Now that exercise has been established as reducing risk, it’s something you can act on. “For each woman, the relative importance of each of the risk factors will vary,” he says. “But overall, for a woman who wants to reduce her risk, exercising is a good strategy. You could also lose weight, but that only seems to be a risk factor in post-menopausal women. I think the area of exercise and breast cancer is important and up until now unappreciated. For many years it’s been controversial but the evidence is firming up.”
As with all emerging areas of scientific knowledge, however, frustrations surround what we don’t yet know. Professor Bernstein cannot be prescriptive on what type of exercise and how much has a protective effect, and research has not yet revealed how long it takes for the protective effect to build up. Professor Bernstein believes, however, that it is exercise in the pre-reproductive and reproductive years that is most significant: in post- menopausal women, it still seems to help but partly because it counters obesity, another risk factor.
And there is a good understanding of why exercise is so influential in the development of breast cancer. Many studies have shown that strenuous physical activity reduces the production of female hormones such as oestrogen from the ovaries. Oestrogen seems to play a key role in the development of breast cancers because it regulates the rate of reproduction of certain types of cells in the breast. This is why hormone replacement therapy, not having children and a late menopause are all risk factors. It’s all to do with how much oestrogen the breast is exposed to.
The cumulative number of ovulatory cycles a woman has in a lifetime is another influence on this. Professor Bernstein believes that how early a girl starts her periods may be an especially important part of this equation. Exercising from an early age can have a beneficial effect because it tends to delay the first period.
“In a study of 14 to 18-year-olds that we did in a high school, we gathered a perfect record of menstruation and how much exercise the girls had done, from going up stairs at home to organised activities at school,” she says. “When you compared the active girls with the inactive girls, they were two to three times more likely to experience, instead of full ovulation, a type of immature menstrual cycle where they don’t ovulate. That means they don’t release oestrogen and progesterone in the same way. So their exposure to the hormones will be lower and their chances of breast cancer in later life will be lower.”
Professor Bernstein says that of 40 reputable studies that have looked at the impact of exercise on breast cancer risk, all but two show a reduction in risk. This reflects a growing acknowledgement of the importance of exercise in preventing cancers generally.
In December, Body&Soul reported on Cancer Research UK’s new emphasis on inactivity increasing cancer risk, regardless of its link with obesity, in response to a review of the evidence by Professor Ken Fox from the University of Bristol. “Just get your girls involved in some physical activity, and support them in after-school activities,” says Professor Bernstein. With a recent survey of secondary school girls finding that just 53 per cent of teenage girls exercise at least once a week, that’s going to be quite a challenge, but one that both schools and parents will have to rise to.
Breast cancer: the facts
For more information on the disease, call Breakthrough Breast Cancer on 08080 100200, or log on to www.breakthrough.org.uk
