How Swimming Might Prevent Cancer

As any swimmer knows, you need to move to improve. The more you train, the faster you get. But new research suggests that practice doesn’t just make perfect—it may actually provide protection against cancer.

A large study published in October 2021 in Medicine & Science in Sports & Exercise, the journal of the American College of Sports Medicine, attempts to quantify the relationship between physical activity and cancer incidence among adults aged 30 and older.

Using self-reported physical activity data from nearly 600,000 adults across the U.S., the researchers determined that 3% of common cancers (including cancers of the kidney, colon, stomach, esophagus, bladder, breast, and uterus) that are diagnosed in the U.S. can be closely linked to inactivity. The study noted that this means an average of 46,356 cancer diagnosis were attributable to inactivity per year.

The researchers determined that stomach cancer was most closely tied to inactivity with nearly 17% of cases resulting from too little movement. Bladder cancer risk, on the other hand, was less tied to inactivity, increasing 4% when the person was less active.

Geographical variations in risk level also emerged from the researcher’s analysis, with individuals in southern states generally reporting less exercise correlating to higher rates of certain cancers linked to inactivity.

The study noted that, at least in theory, if all Americans met or exceeded a recommended five hours per week of moderate physical activity, more than 46,000 cancer diagnoses each year might just disappear. Although the researchers concede this hope is a bit simplistic—cancer is a complex disease that results from a range of factors, and they were quick to note they’re not trying to lay blame for a cancer diagnosis on the individual—the science does seem to suggest that getting more exercise is an important lifestyle change everyone can make to reduce their risk.

A Growing Body of Evidence

Anne McTiernan, a professor at the Fred Hutchinson Cancer Research Center in Seattle and author of “Cured: A Doctor’s Journey from Panic to Peace,” says that exercise has a long-standing reputation as being a great addition to your daily health routine, especially if you’re looking to reduce your risk of certain types of cancer.

She served on “a government committee that determined there’s strong evidence that exercise is associated with a 10% to 20% reduced risk for several cancers, including bladder, breast, colon, endometrial, esophageal adenocarcinoma, kidney, and stomach cancers. In my clinical trials at Fred Hutchinson Cancer Research Center, we’ve found that exercise reduces factors that are associated with cancer risk, such as estrogens, testosterone, insulin, and inflammation markers,” she says.

Although the science hasn’t completely been settled, a clear picture is emerging: Moving more can change the trajectory of your cancer risk over time. Exactly how much movement you need to achieve these benefits is still unclear, McTiernan says. “We don’t know how much exercise is optimal, but our committee recommended that all adults engage in at least 150 minutes per week of moderate intensity exercise, and more is better.”

This recommendation is in line with the recent study and guidelines from the American Cancer Society, which recommends 150 to 300 minutes—that’s 2½ to five hours—of moderate exercise a week to lower your risk of developing cancer. Moderate exercise is defined as a brisk walk or other aerobic activity, which could certainly include swimming.

Although strength training is believed to be great for overall health, the ACS notes that there’s a “paucity of evidence for this type of activity in relation to cancer; thus the focus for cancer prevention guidance is largely on aerobic moderate-to-vigorous physical activity (MVPA).”

Getting regular physical activity can also help while you’re being treated for cancer, McTiernan says. “Clinical trials have shown that in cancer patients and survivors, regular exercise reduces fatigue and improves overall quality of life—how a person feels and thinks. Studies also suggest a benefit for prolonging survival, but that hasn’t been tested in clinical trials, and it could be that cancer patients and survivors who feel better are more apt to exercise.”

How exactly it all works isn’t fully understood, but McTiernan says “some possibilities are reducing insulin resistance and inflammation,” two physiological processes that can contribute to the development and exacerbation of chronic conditions such as cancer.

Although moderate physical activity such as swimming clearly provides a cancer risk benefit and can make you feel better during treatment, not everyone has gotten the message. The ACS notes that “nearly one-half of U.S. adults (46.7%) did not meet the recommended amount of MVPA.”

Moving Against Cancer

Bottom line: Moving more can reduce your risk of cancer and help if you’re receiving treatment. And literally any movement can help. “Any exercise helps, so for people who are not currently exercising or training, anything they can do to start is good,” McTiernan says.

Ultimately, whatever exercise you find sustainable, “the best exercise is something you love and will keep doing,” McTiernan says. “Swimming is an excellent exercise and meets and exceeds the committee’s goals for cancer risk reduction. Plus, the injury risks with swimming are lower than many other sports, so people are less likely to be derailed,” McTiernan says. (She does note that if you’re swimming outdoors, be sure to “liberally apply sunscreen so you don’t increase risk for skin cancer.”)

All that said, although swimming can be a fabulous way to beat cancer, some swimmers might have to sit out for a spell during treatment. For example, if you have an indwelling port for receiving chemotherapy, swimming might not be the best choice, as there’s a potential for infection. In addition, “chlorine could be irritating for patients with skin problems from chemo or radiation,” McTiernan says. But there may be ways to work around these potential problems. If you’re being treated for cancer currently, talk with your treatment team to determine whether continuing to swim or starting swimming is a good choice for your situation.

If you’re looking to reduce the chances that you’ll ever end up having to talk with an oncologist at all, get to the pool and start logging those laps. Hitting the target of five hours of activity a week is just a few Masters workouts away.