Fitness may lower breast cancer risk

Findings offer tantalising new clues into relationship between fitness, exercise and malignancies

Aerobic fitness seems to alter the interior workings of cells in ways that may substantially lower the risk of breast cancer.

A new study with female rats found that those that were the most fit were much less likely than other animals to develop cancer after exposure to a known carcinogen, even if they did not exercise.

The findings offer tantalising new clues into the relationship between fitness, exercise and malignancies.

Most of us probably think that cardiovascular fitness, which in broad, scientific terms is the ability to get oxygen and energy to muscles, is built with diligent exercise, and that the more we work out, the fitter we become. But we would be only about half right. A large percentage of our aerobic fitness, perhaps as much as half, according to some studies, is innate. This genetically determined fitness level varies widely from family to family and person to person. Exercise can augment it, while avoiding movement and gaining weight may reduce it, but a person’s baseline, genetic fitness is his or hers from birth.

In recent years, scientists have become interested in how our innate fitness might affect our overall health, and also why. Many studies have established that people with high fitness are at lower risk for a wide range of diseases, including many types of cancer. But whether their disease protection results from regular exercise or from a fortunate genetic heritage — or both — has been unclear.

For the new study, which was published in July in Carcinogenesis, researchers at Colorado State University, Memorial Sloan Kettering Cancer Center in New York City and the University of Michigan opted to focus on breast cancer. Epidemiological studies have shown that being physically fit is associated with lower risk for the disease, but not why.

Because they wanted to examine the role of innate fitness in the disease, the scientists turned to a famous strain of rats bred by Lauren Koch and Steven Britton at the University of Michigan. Over multiple generations, these rats were tested on treadmills. Those that ran the farthest before tiring were subsequently mated with one another, while those that pooped out early likewise were paired up, until, ultimately, the pups displayed a large difference in inborn fitness.

The researchers used female pups born to mothers with either notably high or low aerobic capacity. These young animals did not exercise, so their fitness depended almost exclusively on genetics.

Before the pups reached puberty, they were exposed to a chemical known to be a potent breast cancer trigger. The researchers then checked them frequently for palpable tumors throughout adulthood. They also looked, after the animals’ deaths, for signs of malignancies that had been too small to feel and microscopically examined breast cells for various markers of cell health.

You agree to receive occasional updates and special offers for The New York Times’s products and services. The differences between the animals with high and low fitness turned out to be striking. 

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