Even mild exercise can reduce the risk of breast cancer

Researchers from the University of North Carolina (UNC) have found that physical activity, whether mild or intense and carried out either prior to or following the menopause, can reduce the risk of breast cancer. However, the findings, published online in the journal CANCER, also show that substantial weight gain has the potential to negate the positive effects of physical activity.

A team from the UNC Gillings School of Global Public Health in Chapel Hill, studied over 3000 women aged between 20 and 98, 1504 of whom had breast cancer and 1555 of whom did not. The data was collected as part of the Long Island Breast Cancer Study Project. The researchers found that women who exercised, whether during their reproductive or postmenopausal years, were less likely to develop breast cancer than those who did not. Those who exercised between 10 and 19 hours per week experienced the greatest benefit with a risk reduction of approximately 30 per cent. Even so, reductions were identified at all levels of intensity.

Although previous studies have demonstrated that exercise can reduce the risk of breast cancer, questions remained over how frequent, how long and how intense this exercise had to be in order to become beneficial. Neither was it understood whether physical activity reduced the risk of breast cancer in all body types, or whether all types of this cancer were affected by exercise.

I spoke to Lauren McCullough, one of the study’s authors, to find out more about the ways in which physical activity can reduce one’s risk of developing breast cancer…

Your findings show that physical activity reduces the risk of breast cancer both in women who exercise during their reproductive years and in those who do so during their postmenstrual years. Did either group benefit significantly more than the other?
Actually, neither did. We examined mutually exclusive categories and in both of these, there was approximately a 30 per cent risk reduction amongst women in the third quartile – those who exercised between 10 and 19 hours per week. Neither group benefited more than the other.

Were you surprised by the extent to which weight gain can negate the positive effects of physical activity?
I can’t say that we were really surprised because we knew that weight gain – especially during the postmenopausal years – can be particularly harmful. Most of the time, this takes the form of visceral fat that accumulates over the central abdomen and this type of fat is metabolically active. Physical activity did help to reduce the risk of developing breast cancer, but it didn’t actually cross over the null value to become a risk reduction.

What did come as a surprise was that amongst women who were obese, physical activity brought their risk back to null, or approximately the same as women of a normal weight who didn’t exercise at all. I think that this is of great benefit and represents an important public health message.

Do you think that your results support the notion that it is never too late to embark upon a more active lifestyle?
I certainly do. This was one of the aims of our study from the beginning. Breast cancer is a disease that tends to be associated with ageing, and many women don’t think about the fact that they are at risk until they are postmenopausal. It is really important for people to know that even if they weren’t active before, it is not too late to go ahead and get started; they can still reap the benefits of exercise. This is the message that we want people to take away from our findings.

Do you have any further research planned in this area?
Actually, I do. I am currently exploring some of the mechanisms that underlie the association between exercise and the reduced risk of breast cancer. Why is there an inverse association between the two? Is it driven purely by obesity or is there an effect of exercise that does not affect adiposity? Now that a connection has been established, I want to find out more about the mechanisms involved.