More than two million women in the United States have been diagnosed and treated for ]]>breast cancer]]> . The likelihood of survival following a breast cancer diagnosis varies greatly, depending on such factors as stage of the cancer, tumor size, estrogen receptor status, and age.

Recent research also suggests that lifestyle factors, such as physical activity, may influence survival. Some researchers believe that the ability of physical activity to decrease levels of circulating estrogen, which stimulates breast cells to multiply, may explain this link. However, few studies have specifically looked at the relationship between physical activity and breast cancer survival, and no studies have examined the effect of different levels of physical activity on survival.

A new study in the May 25, 2005 Journal of the American Medical Association set out to determine whether higher levels of physical activity after breast cancer diagnosis is associated with longer survival. Their findings showed that women who partook in exercise equivalent to walking for one or more hours per week were more likely to survive than women who exercised less than that.

About the Study

The researchers identified 2,987 women, all taking part in the Nurses’ Health Study, who had been diagnosed with stage I, II, or III invasive breast cancer between 1984 and 1998. They then followed these women until death or June 2002, whichever came first.

Every two years, starting at least two years after their diagnosis, participants filled out questionnaires that asked about the amount of time they spent doing common activities such as walking, bicycling, swimming, or playing tennis each week. The researchers assigned each activity a metabolic equivalent task (MET) score based on its energy expenditure. For example, walking at an average pace was equal to a MET score of three, while running was equal to a MET score of 12. Based on the average weekly MET scores, the researchers classified the women into five different levels of activity and compared activity levels to rates of death and breast cancer recurrence.

The Findings

During the study period there were 280 deaths due to breast cancer and 370 breast cancer recurrences. Overall, physical activity was associated with a greater chance of survival. Women who engaged in moderate amounts of weekly exercise—the equivalent of walking 3-5 hours per week—experienced the greatest benefit, reducing their risk of death from breast cancer by half.

The table below summarizes how much varying levels of physical activity reduced the likelihood of breast cancer mortality compared to less than one hour of walking per week (or the equivalent).

Physical activity (in MET-hours per week)

Equivalent hours per week of average paced (2-2.9 miles per hour) walking

Reduction in risk of death


1-3 hours



3-5 hours



5-8 hours


≥ 24

≥ 8 hours


The researchers also found that:

  • The effect of physical activity on overall survival and breast cancer recurrence was similar to its effect on breast cancer mortality.
  • Women with hormone-responsive breast cancer were especially likely to benefit from physical activity.
  • Overweight and normal weight women experienced an equal degree of protection from physical activity.
  • Women who were more active had a lower body-mass index (a measure of ideal body weight), consumed more protein, and were less likely to have gained weight between time of diagnosis and time of activity assessment.

How Does This Affect You?

This study suggests that engaging in physical activity not only reduces the risk of breast cancer, but improves the chances of survival after it is diagnosed. And this protective effect may occur with even minimal increases in activity.

It should be noted that this was an observational study, which means that researchers only observed an association between different levels of physical activity and probability of death or cancer recurrence; there could have been other factors associated with exercise that led—or contributed—to the observed effect. For instance, women who exercised a moderate amount may also have had better diets or lower amounts of stress in their lives, than women who exercised less or more.

Still, there is enough evidence to suggest a link between physical activity and breast cancer. Whether you are looking to prevent breast cancer or extend your survival following a diagnosis of breast cancer, the choices you make in your day-to-day life actually do seem to matter. This is welcome news for a disease best known for making us feel so helpless and out of control.