Moderate exercise appears to reduce breast cancer risk: Q

A new study from researchers at the University of North Carolina’s Gillings School of Global Public Health teases out the benefits of exercise in preventing breast cancer, attempting to describe exactly how much exercise at what period of life seems to have the most benefit.

The report has some good news for women: Even moderate levels of physical activity — during childbearing years or after menopause — may reduce breast cancer risk. But weight gain in later life may negate some of the benefit, the team cautioned.

Booster Shots spoke with study coauthor Lauren McCullough, a doctoral candidate who studies cancer epidemiology at the University of North Carolina, Chapel Hill, about the results, which were published online Monday in the journal Cancer (and are available to subscribers here).

Why this study? We already know that exercise is associated with lower breast cancer risk, right?

Yes, we do know that physicial activity is inversely associated with breast cancer — but we didn’t know the time period at which women needed to be active in order to receive the benefits, or how much activity was required or what the intensity level of that activity needed to be.

We also didn’t know whether the association was different for women who were overweight or underweight or had gained weight or lost weight.

So how did you conduct the analysis?

I used data from the Long Island Breast Cancer Study project. There were around 1,500 cases [women who had been diagnosed with breast cancer] and 1,500 controls [women without breast cancer]. At the time that they were interviewed they were asked about activities that they had engaged in across the lifespan.

It was a very detailed questionnaire, and it was interviewer-administered and very systematic.

Your study focused on the women’s “recreational physical activity.” Why?

We were specifically trying to get at activities that women do on their own time that were not related to occupational status — any time that they spent doing sports, team sports, running, jogging, walking, biking, even gardening. Our study population in particular is pretty homogeneous with respect to race (they’re primarily Caucasian) — and with respect to socioeconomic status (most of the women have higher socioeconomic status than the U.S. population.) Looking at occupational activity wouldn’t give us a wide enough range of variation to see results.

What did you find?

First, that exercise at any intensity level during the reproductive and post-menopause years has the greatest benefit for reducing breast cancer risk. For both of those time periods we saw about a 30% risk reduction for women in the third quartile of activity [10-19 hours of activity per week.]

The second thing was that when we looked at physical activity with respect to body size, we found that even women who are classically defined as being overweight based on body mass index received a benefit from being physically active. Granted, it wasn’t as large of a risk reduction as for women who were classified as normal weight, but I stil think that is an important public health message.

Women who were obese—with a BMI over 30— weren’t at reduced risk, but their risk was basically flat. Their risk was essentially the same as a normal weight woman who wasn’t exercising at all.

Women who were obese and weren’t active were at an increased risk.

The final observation is that weight gain may eliminate some of the beneficial effects of regular activity. Women who gained a substantial amount of weight didn’t have risk reductions, even if they were defined as being highly active in our study.

This is postmenopausal weight gain?

Yes. We looked at our women to see who had maintained, who had gained and who had lost weight. And the overwhelming majority of the women had gained more than 3 kilograms [6.6 pounds] since menopause.

No matter where you fall on the BMI spectrum, the important thing for postmenopausal women is not to gain additional weight.

What would you like women to take away from your work?

Primarily that they don’t have to feel like they have to be marathon runners to receive this benefit. With just moderate activity, like walking a dog or taking the steps instead of the elevator, you can receive a benefit — whether you’re normal, overweight or obese

I think particularly in the postmenopausal years it can be very discouraging if you’re classically defined as overweight or obese and you’re exercising and you’re not seeing that weight fall off. But even though you’re not losing the pounds it doesn’t mean that physical activity isn’t still benefiting you.