Summary

Physical activity reduces the risk of breast cancer overall. However, as a new study shows, certain groups have more to gain from exercise than others. Women who do not carry an excess of body weight who do sport in their spare time have the lowest risk, especially if they have already been through the menopause.

Introduction

Over 80 studies have been conducted around the world that show that exercise can reduce the risk of breast cancer. However, we need to know more - what kind of activity is most beneficial, which women have most to gain and so on. Then a woman can choose how to take exercise and how physical activity rates with other risk factors influencing this common disease.

What was done

Researchers led by Christine Friedenreich of the Alberta Cancer Board, Canada, carried out a wide ranging review of the medical literature on physical activity and breast cancer. They looked for indicators of the type, duration and intensity of activity. They also recorded menopausal status, body mass index, racial group and family history of breast cancer where this information was available.

What was found

This study revealed that physical activity reduced the risk of breast cancer by 25 percent. All types of activity were associated with a reduction in risk. But recreational activity was more strongly linked to benefit than either occupational or household activity - the gym or tennis rather than housework, in other words. Both moderate and vigorous activity were linked to equal benefit - good news if you prefer to take things a little more slowly. Staying active throughout your life, and particularly continuing after menopause, conferred special benefit too. Therefore, naturally 'sporty' types have an edge. Lean women seemed to have more to gain from exercise than those who were overweight and the obese did not seem to benefit at all.

What this study means

The researchers were not able to determine exactly how exercise modifies the risk of breast cancer. Indeed, they believe that there may be different mechanisms involved depending upon dose and timing of the activity. But they have some ideas. Maybe exercise reduces levels of hormones like estrogen which could, in turn, reduce tumor risk. It could also improve insulin sensitivity, or reduce inflammation, or otherwise modify biochemical pathways in the body. There's a certain amount of laboratory and clinical evidence for all these theories, although more specific studies are probably needed. The take-home message for women is, if you are active keep on moving to reduce your risk of breast cancer. If your exercise is confined to your regular work or home routine, why not find a sport to do as a hobby as well? And if you have become less active as you have got older, it would be well worthwhile taking up some gentle exercise.