Issue 28, Winter/Spring 2016
In largest such study ever conducted, effect held even when researchers accounted for weight, smoking status
The largest study of its kind finds that people who exercise regularly may reap a dividend, cutting their odds for 13 types of cancer.
The research involved a pooled analysis of data from 12 prospective U.S. and European studies that together followed more than 1.4 million people for a median of 11 years.
Compared to participants in the bottom 10 percent in terms of physical activity, those in the top 10 percent had markedly lower risks for cancers of the liver, lung, kidney, gastric cardia (upper stomach), endometrium (uterine lining), colon, head-and-neck, rectum, bladder and breast, as well as lower risks of myeloma, esophageal adenocarcinoma and myeloid leukemia.
The reductions in risk weren’t simply because the “high-exercisers” were thinner than their more sedentary peers, or less likely to smoke, the researchers said.
“Most of these associations were evident regardless of body size or smoking history,” wrote a team led by Stephen Moore, PhD, of the U.S. National Cancer Institute. They published their findings earlier this year in JAMA Internal Medicine.
As the researchers noted, prior studies have found strong links between higher rates of leisure-time physical activity and decreased risks for colon, endometrial and breast cancers.
However, the new study assessed the benefits of exercise against a broad range of tumor types, gathering data on a huge number of people tracked prospectively.
The report found especially high rates of risk reduction – 20% or more – for the “top exercisers” for seven different tumor types: esophageal adenocarcinoma (42% reduction), liver (27%), lung (25%), kidney (23%), gastric cardia (22%) endometrial cancers (21%) and myeloid leukemia (20%).
There were less dramatic, but still significant, reductions in risk for six other tumor types – myeloma, colon, head and neck, rectal, bladder and breast.
Overall, a person’s odds of developing any cancer fell by 7% if they exercised at a high level, the researchers reported.
The risks for melanoma actually rose for the high-exercisers, Moore’s team noted. However, the 27% higher risk for the skin cancer observed in this group may be, “because physical activity is frequently done outdoors in light clothing,” the researchers reasoned.
Factoring in a person’s body mass index (BMI) didn’t seem to affect the results for most tumor types. And that’s important, the researchers said, “because not all persons who engage in high levels of physical activity have low body weights.”
Lauren McCullough, PhD, Kathleen McClain, MS, and Marilie Gammon, PhD wrote an accompanying journal commentary. They said the findings are “exciting,” but raise as many questions as they answer.
For example, “issues that remain unclear are the exact timing, intensity, and dose of physical activity required for cancer risk reduction,” they said. As well, the “underlying mechanism” driving the link between physical activity and cancer prevention remains largely unknown.
Finally, they said, what types of exercise – walking, biking or other activities – work best, and for how long?
“It is currently unknown whether physical activity should be initiated during adolescence, can be intervened on during mid-life, or must be sustained across the entire life course to reduce the risk of cancer development,” the experts wrote.
One thing is clear, however: far too few people get enough exercise.
According to one 2012 study, 51 percent of Americans and 31 percent of people worldwide fail to meet recommended physical activity levels.
According to Moore’s team, that means that, “promotion of physical activity may be important for population-wide cancer prevention.”