Never Too Late for Exercise to Cut Breast Cancer Risk

Nick Mulcahy

August 21, 2014

It's never too late to get moving and somewhat reduce breast cancer risk.

That's the message from a prospective cohort study of 59,000 postmenopausal women in France.

The researchers found that women who undertook moderate levels of exercise — the equivalent of at least 4 hours a week of walking — had a 10% reduction in the risk for invasive breast cancer, compared with less active women (hazard ratio, 0.90; 95% confidence interval, 0.82 - 0.99).

Notably, the risk reduction occurred only in postmenopausal women who were active "recently" (within the previous 4 years) at this level of exercise.

No risk reduction was found in women who had achieved this level of exercise 5 to 9 years earlier but who had then slacked off, which suggests that recent and continuous exercise is what counts.

"My advice to women who do not yet exercise is that you can benefit from starting right now, even though you did not exercise before," senior researcher Sylvie Mesrine, MD, from the Institut Gustave Roussy, in Villejuif, France, told Medscape Medical News in an email.

Clinicians can even tell patients that no workout gear is required.

"It does not need to be very complicated or strenuous. Just find an easy way to walk at a lively pace at least 30 minutes per day, like getting off the bus 1 stop earlier or not taking your car to do some shopping," said Dr. Mesrine.

The study was published online August 11 in Cancer Epidemiology Biomarkers and Prevention.

The researchers analyzed data from 59,308 women who were followed from 1993 to 2005 with biennial health and lifestyle questionnaires. The average postmenopausal duration was 8.5 years.

During the study period, 2155 of the women developed invasive breast cancer.

Most of the women in the study cohort were school teachers and were covered by a national health insurance fund. This population might be a limitation, Dr. Mesrine and colleagues acknowledge.

 
The women participating in the cohort are fairly slender teachers.
 

"The women participating in the cohort are fairly slender teachers," they write. About three-quarters of the group (76%) had a body mass index (BMI) below 25 kg/m².

Nevertheless, the risk reductions seen in the study were of the same order of magnitude, regardless of BMI, weight change, waist circumference.

The types of activity reported by participants in their biennial questionnaires were either "walking" or "cycling/sports."

There was no apparent "dose–response relationship" — that is, exercising more strenuously did not increase the reduction in breast cancer risk. However, the researchers acknowledge that the questionnaire gathered only "limited information" about the intensity of the women's leisure activities.

"Our results suggest a decrease in risk associated with recreational physical activity even at modest levels," Dr. Mesrine and colleagues report.

The study addresses unknowns in the literature about breast cancer and exercise.

"Physical activity is thought to decrease a woman's risk for breast cancer after menopause," said another of the study researchers, Agnès Fournier, PhD, also from the Institut Gustave Roussy, in a press statement. "However, it was not clear how rapidly this association is observed after regular physical activity is begun, or how long it lasts after regular exercise stops."

The study indicates that the onset of benefit is "relatively rapidly" (within 4 years of initiation) and that the reduction "may disappear a few years after the activity stops," the researchers note.

Dr. Mesrine and colleagues practice what they preach.

"Most members of the research team regularly exercise — and so do I — at least as much as the minimum WHO recommendations. Some cycle to work, others walk, and most of them also practice some sport," said Dr. Mesrine.

France has become more exercise-friendly in recent years. "Much progress has been made over the last decade to encourage exercising," Dr. Mesrine explained. For example, in most cities, bicycles can be rented at a low price and can be left at anywhere.

This study was supported by funds from Institut National du Cancer, the Fondation de France, and the Institut de Recherche en Santé Publique. The authors have disclosed no relevant financial relationships.

Cancer Epidemiol Biomarkers Prev. Published online August 11, 2014. Abstract

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