Exercise reduces the risk of breast cancer in most women
Studies have shown that exercise can help to reduce the risk of breast cancer, but a new review has found that some groups of women benefit more than others.
Research published in the British Journal of Sports Medicine analysed 62 published studies on the impact of physical activity on breast cancer risk.
CM Friedenreich from the Alberta Cancer Board in Canada and AE Cust of the University of Melbourne in Australia found that the risk of breast cancer was approximately 25 per cent lower in women who were the most active compared with those who were the least active in over two thirds of the studies.
While all types of activity had a beneficial effect, recreational activity such as taking part in sports had a greater protective effect than routine activity such as housework or work-related activity.
All women except those who were obese benefited from physical activity, and the greatest impact on breast cancer risk was found in those with a body mass index (BMI) of less than 22, bearing in mind that the healthy range is widely regarded to be between 18.5 and 25.
The lowest risk of breast cancer was found in women who had undertaken a lot of recreational activity throughout their life, and activity performed after the menopause had a greater effect than that performed earlier in life.
The authors wrote: "We have comprehensively examined all parameters of physical activity (duration, frequency, intensity), type of activity (occupational, household, recreational), time periods in life and possible effect modification that have not been thoroughly reviewed before." The experts believe that the effect of physical activity on breast cancer risk is likely to be complex and suggest a number of possible mechanisms, including effects on sex hormones, insulin-related factors, the immune system, and other hormone and cellular pathways.