by Jones P

Although nobody can predict with 100% accuracy who will develop cancer, there are many risk factors we do know about. Risk factors are things that increase your risk for developing a particular illness, such as cancer. Some risk factors, like age or genetics, cannot be changed, but other lifestyle-oriented risk factors can. Certain dietary and activity habits have been repeatedly shown to alter health risks, including the development of some types of cancer. Physical activity is associated with a wide range of health benefits, although it is still debated what the best type, amount, or intensity of exercise is.

The Nurses Health Study is a large cohort trial that followed lifestyle habits and health outcomes of several female nurses over a long period of time. In a study published in Archives of Internal Medicine, investigators found that moderate physical activity was associated with a lower risk of breast cancer.

About the Study

The Nurses Health Study is a large cohort trial. This investigation included 95,396 postmenopausal women. Over a 20 year follow-up, 4,728 women developed a case of invasive breast cancer. The self-reported physical activity habits of the women that developed cancer were compared to activity in women who did not develop cancer. Investigators found the following trends:

  • Women with one hour of physical activity per day (at an intensity of a brisk walk) had a lower risk of breast cancer compared to women with less than one hour of physical activity per week.
  • In women who were least active at menopause (about 30 minutes of average pace walking on most days), women who increased physical activity after menopause had a lower risk of breast cancer compared to women who did not increase activity after menopause.

How Does This Affect You?

This type of study is an observational study. The investigators do not interfere or introduce an element into the study. Instead, they gather information over a long period of time and looked for associations. This type of design helps to make connections but cannot be used to determine a cause and effect relationship. The Nurses Health Study is a very large cohort done over a long period of time. Although it has the limitations of any observational trial, it has produced important associations.

Important findings from this study are that simple activities like walking were associated with reduced risk, and women who increased their activity level after menopause were also able to decrease their risk. It is never too late to start exercising. Begin slowly and build up your activity level. Carve out some time each day for some activity and add little pieces throughout the day by taking the stairs instead of the elevator, parking a little further away, or walking instead of taking a car. If you are going to start a new exercise program, it is always a good idea to talk to your doctor first.


American Cancer Society 


Eliassen AH, Hankinson SE, Rosner B, Holmes MD, Willett WC. Physical activity and risk of breast cancer among postmenopausal women. Arch Intern Med. 2010 Oct 25;170(19):1758-64.

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