Physical activity, exercise and breast cancer

Physical activity and weight

In breast cancer, women become less active following diagnosis and this behaviour is even more pronounced in women who are already overweight¹. Weight gain is common in the year after diagnosis, especially among those receiving therapies such as chemotherapy, radiotherapy and hormonal therapy². Being overweight, both before and after diagnosis, has been linked to poorer survival rates and an increased risk of recurrence. However, side effects such as nausea, pain and fatigue from these therapies can make it difficult for women to maintain a healthy weight. Regular physical exercise has been observed to increase lean body mass, decrease body fat and help maintain bone mineral density³.

Hormonal benefits

Lower levels of ovarian hormones such as oestrogen and progesterone have been associated with physical activity⁴. It has been found that exercise significantly reduces the amount of oestrogen in the blood of postmenopausal women⁵. It can also increase levels of a protein (sex hormone binding globulin) that binds to oestroegen making less available to breast tissue⁶. This may be an explanation how physical activity lowers the risk of developing breast cancer.

Raised insulin levels have been linked with increased risk of breast cancer recurrence and death. As it has been found that insulin levels are lower in women who exercise, this may be another mechanism that explains the relationship between physical activity and breast cancer prognosis. Furthermore, high levels of proteins called insulin-like growth factors have also been linked to an increased risk of premenopausal breast cancer and breast cancer recurrence and survival⁷,⁸. However, studies looking at these proteins and physical activity have been inconsistent and need to be further investigated.

Mammographic density

Mammographic density is a strong risk factor for breast cancer⁹. One study among very overweight breast cancer survivors found that those who were physically active were less likely to have mammographic breast density¹⁰. Results from other studies have been inconsistent however.

Breast cancer survival

Physical activity's influence on the prognosis of early breast cancer survivors was investigated in an American study which found that women who were physically active for 2.5 hours per week after diagnosis had approximately 67% lower risk of death from all causes¹¹. Another study found that women who had survived breast cancer and were physically active for 2.8 hours or more per week had a significantly lower risk (35-49%) of dying from breast cancer¹². These findings were echoed in the Nurses Health Study which found that women with breast cancer who walked for 3-5 hours a week had better survival and lower recurrence rates than those who exercised less¹³. A further study examined a combination of diet and exercise with similar results. Women who ate 5 or more servings of fruit and vegetables a day and were physically active for 30 minutes for 6 days a week had a higher survival rate than those who did not¹⁴.

Summary

There is some good evidence to demonstrate that physical activity can reduce the risk of post-menopausal breast cancer and there may be benefits for women after diagnosis including improved prognosis. However evidence for an association between physical activity and premenopausal breast cancer risk is still inconsistent. Physical activity can increase lean body mass, decrease body fat, lower oestrogen levels and insulin levels while improving breast cancer prognosis. More research is required to clarify the optimal intensity, duration and type of physical activity for women with breast cancer.

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