If you didn’t make a New Year’s resolution to exercise regularly, here’s one (of many) good reasons you may want to do so now: A major new analysis of nine previous studies has found that meeting current physical activity recommendations is associated with a reduced risk of at least seven different types of cancer.
The study, published in the Journal of Clinical Oncology, also found that the longer and more vigorously people exercise, the greater the drop in cancer risk.
The authors of the study — a team of researchers from the National Cancer Institute, the American Cancer Society and Harvard University — urge doctors and other health care practitioners to encourage people to adopt and maintain physical activity at recommended levels to lower their risk of cancer.
In the U.S., those recommended levels — for adults — are at least 2.5 to 5 hours of moderate-intensity activity or 1.25 to 2.5 hours of vigorous-intensity activity each week.
Less than a quarter of American adults meet those recommended levels, however.
Importance of findings
Does this study sound like old news? Well, it is and it isn’t. It’s true that scientists have known for some time that regular physical activity is associated with a lower risk of breast and colon cancer, and in recent years they have expanded that link to include several additional cancers, most notably those involving the uterus, bladder and kidney.
But they had not been able to determine the amount and intensity of activity needed to help that risk drop — and, more specifically, if the amounts recommended in guidelines are sufficient.
“Physical activity guidelines have largely been based on their impact on chronic diseases like cardiovascular disease and diabetes,” explains Alpa Patel, one of the study’s authors and senior scientific director of epidemiology research at the American Cancer Society, in a released statement.
“These data provide strong support that these recommended levels are important to cancer prevention, as well,” she added.
How the study was done
For the study, Patel and her colleagues pooled data from nine studies involving more than 750,000 people living in the United States, Europe and Australia. In each study, the participants self-reported their leisure-time physical activity and were then followed for an average of 10 years to see if they developed one of 15 types of cancer.
An analysis of all that pooled data revealed that compared to people who did not exercise, those who met the recommended levels of leisure-time physical activity were less likely to develop seven cancers: breast, colon, endometrial (uterine), kidney, liver, myeloma and non-Hodgkin lymphoma.
For women, the risk of breast cancer fell by as much as 10 percent, while the risk of endometrial cancer dropped by as much as 18 percent. (The link with endometrial cancer disappeared, however, after the researchers adjusted for body mass index, or BMI.)
For men and women, meeting the recommended levels of activity lowered the risk of kidney cancer by up to 17 percent, myeloma by up to 19 percent and liver cancer by up to 27 percent.
Physical activity was also associated with up to a 14 percent reduced risk of colon cancer — but only in men. And it was linked to up to an 18 percent reduction of risk of non-Hodgkin lymphoma — but only in women.
For several of these cancers — specifically, breast, colon and endometrial — the study’s findings revealed a “dose/response” relationship. In other words, the more vigorous the level of activity, the lower the risk.
Limitations and implications
The study comes with plenty of caveats. Most notably, it is observational, which means it can’t prove a cause-and-effect relationship between physical activity and cancer risk. Also, although the data came from hundreds of thousands of people, the number who developed some of the cancers was limited, a factor that may have affected the findings.
In addition, the participants self-reported their physical activity levels. Such reports can be inaccurate. And most of the participants were white. The findings may not be applicable, therefore, to other racial and ethnic groups.
Still, the study’s results are in line with other research on this topic, including a large 2016 National Cancer Institute study that tied high levels of exercise with a lower risk of developing 13 types of cancer.
Why physical activity reduces cancer risk is unclear, but, as Patel told HealthDay reporter Steven Reinberg, there are several possible explanations.
“The most common things that we know about exercise, even in the absence of weight maintenance or weight loss, is that it’s important for insulin regulation, sex hormones like estrogen, and also has an important impact on inflammation and immune response — any or all of these different factors could affect different types of cancer,” she said.
Of course, exercise is only one of several modifiable risk factors associated with a reduced risk of cancer. Others include not smoking, eating healthful foods, maintaining a healthy weight and avoiding or limiting the use of alcohol.
And, yep, those should go on your New Year’s resolution list, too.
FMI: You can read the study in full on the Journal of Clinical Oncology website.