Regular exercise may do more than strengthen muscles — it could also help the body fight cancer. A new study from Duke-NUS Medical School in Singapore found that exercise restored natural tumor-fighting signals in aging muscles, slowing cancer growth in mice. Although the findings are promising, the research was conducted in mice and fruit flies, so more studies are needed to determine whether the same effects occur in humans.

Researchers identified a tiny RNA molecule called miR-7a-5p, which helps suppress tumor growth but declines with age. The molecule is found in several tissues throughout the body, including skeletal muscle. According to Study Finds, exercise stimulates muscles to release tiny particles, known as extracellular vesicles, that carry miR-7a-5p throughout the body — particularly in older adults who have age-related muscle loss.

The findings, published in Nature Communications, suggest that exercise can reactivate the pathway that controls the release of these vesicles, restoring some of the body's natural cancer-protective signaling. Extracellular vesicles are tiny membrane-bound sacs that carry proteins, genetic material, and other molecules between cells, allowing them to communicate with one another.

The researchers focused on sarcopenia, the age-related loss of muscle mass and strength. They found that aging muscles affected by sarcopenia released fewer extracellular vesicles, and those vesicles contained lower levels of miR-7a-5p, reducing their ability to help suppress tumor growth.

Previous observational studies have found that people with sarcopenia have a higher risk of developing several cancers, including lung, colorectal, stomach, pancreatic, and esophageal cancers. In the new study, older mice injected with human colorectal cancer cells developed much larger tumors than younger mice given the same injections.

When researchers blocked the release of extracellular vesicles in the younger mice, their tumors grew to nearly the same size as those in the older mice, suggesting that miR-7a-5p plays an important role in slowing tumor growth. Conversely, treadmill running and wheel exercise restored vesicle production in older mice and slowed tumor growth.

"Clinically, we observe an association between advanced cancer and low muscle mass. This is a novel study which illustrates how healthy muscle can potentially inhibit tumor growth," said Dr. Kenon Chua, one of the authors of the study, according to a news release. "We observe that healthy muscles secrete many physiologically important molecules. With advanced age, it is even more important to engage in regular resistance and aerobic exercises in order to maintain healthy muscle volume. This is important not only for function and mobility, but also for general health."

While researchers caution that more studies are needed to determine whether the findings apply to people, the study adds to growing evidence that regular physical activity offers important health benefits as we age — including maintaining muscle mass and potentially reducing cancer risk.