Exercise appears to change the way women's bodies metabolise the hormone
oestrogen, and this could help explain how aerobic activity reduces a woman's
breast cancer risk, a new study suggests.
Previous research has suggested that exercise lowers breast cancer risk, but
there haven't been any clinical studies that explain the mechanism behind this,
said Mindy Kurzer, a professor in the department of food science and nutrition
at the University of Minnesota in Saint Paul.
"Ours is the first study to show that aerobic exercise influences the way our
bodies break down estrogens to produce more of the 'good' metabolites that lower
breast cancer risk," she said.
How the study was done
The study included nearly 400 healthy, but inactive young women who were
divided into two groups. All were premenopausal, meaning their bodies still
produced the hormone oestrogen.
One group remained inactive while the other group did 30 minutes of
moderate-to-vigorous aerobic exercise five times a week for 16 weeks. For their
workouts, they used equipment such as treadmills, stair steppers and elliptical
Before and after those 16 weeks, the researchers collected urine samples from
women in both groups. At the end of the study, the women in the exercise group
had higher levels of the oestrogen metabolites that reduce breast cancer
"Exercise, known to favour fitness and improve heart health, is also likely
to help prevent breast cancer by altering oestrogen metabolism," Kurzer said in
a news release from the American Association for Cancer Research.
"It is very important, however, to decipher the biological mechanisms behind
She is currently conducting similar studies in women at high risk for breast
The US National Cancer Institute has more about breast