Women who are physically active are 25 percent less likely to develop breast cancer, a new study has found.
However, researchers also discovered that certain groups are more likely to see these benefits than others.
The findings showed that the type of activity undertaken, at what time in life and the woman's body mass index (BMI) will determine how protective the activity is against the disease.
Lean women who play sport or undertake other physically active things in their spare time, particularly if they have been through the menopause, have the lowest risk of breast cancer, the study found.
The researchers reviewed the literature and analysed 62 studies looking at the impact of physical activity on breast cancer risk.
They then examined the findings to find out how breast cancer risk appeared to be affected by type of activity, intensity of activity, when in life the activity was performed and other factors.
They found that overall, women who were the most physically active had about a 25 per cent reduced risk of developing the disease versus women who were the least active, reports the British Medical Journal.
Even though vigorous, recreational exercise was linked to the greatest reduction in risk, moderate activity, work-related activity and household chores all lowered the risk for breast cancer.
Women who had undertaken a lot of physical activity throughout their life had the lowest risk of breast cancer, and activity performed after the menopause had a greater effect than that performed earlier in life.
Physical activity reduced breast cancer risk in all women except the obese and had the greatest impact in lean women.
Women who were mothers, had no family history of breast cancer, were not white and had oestrogen receptor negative tumours also had a reduced risk of breast cancer.
The authors said the way in which physical activity protected against breast cancer was likely to be complex and may involve effects on sex hormones, insulin-related factors, the immune system and other hormone and cellular pathways.
The study is published online ahead of print in the British Journal of Sports Medicine.