The Cooper Institute
 

Founded in 1970 by the "Father of Aerobics"
Kenneth H. Cooper MD, MPH

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Does Physical Activity Relate to Cancer Risk?

Posted in
Live well

Thursday, Nov 17, 2016

Cancer is the second leading cause of death in the United States, as well as in most industrialized countries. It has long been known that regular physical activity (PA) decreases the risk of all-cause and cardiovascular disease mortality. While it has also been established that PA decreases the risk of colon, breast, and endometrial cancers, much less is known about the relationship between PA and other less common cancers. Some of this limited knowledge stems from the fact that many previous studies either had a relatively small sample size, used different measures of PA (e.g., occupational PA versus leisure-time PA), or had other methodological differences. A recent paper (Moore et al., 2016) combined data from 12 large U.S. and European studies which examined the relationship between leisure-time PA and risk of developing 26 different types of cancer. Leisure-time PA is defined as activities done at an individual’s discretion that improve or maintain fitness or health. Participants in this study included 1.44 million individuals who were healthy at baseline. Their average age was 59 years; females comprised 57% of the participants. Time spent per week in moderate and/or vigorous leisure-time physical activity was assessed via validated questionnaires at baseline. Average follow-up time was 11 years, during which time 186,932 cases of cancer occurred.  These cases were identified by follow-up questionnaires, review of medical records, and by links to cancer registries. 99% of the reported cancer cases were confirmed. Twenty-six cancer types were selected for analysis.

In general, higher levels of leisure-time PA were related to younger age, higher levels of education, lower Body Mass Index (BMI), and not smoking. When comparing individuals within the lowest 10% of PA to those within the highest 10% of PA, higher levels of PA were related to a significant reduction in the risk of developing 13 of the 26 types of cancer (Table 1).  For 7 of these cancers, the risk reduction was 20% or more, while a 10-20% reduction in risk was seen for the remaining 6. It is important to mention that variables such as age, smoking, race/ethnicity, and alcohol intake that might have ‘muddied the waters’ were carefully controlled for during these analyses. Thus, PA was shown to have an independent and strong relationship with the 13 types of cancer listed in Table 1. Of interest, risk of developing malignant melanoma was increased by 27% within the highest PA group as compared to the lowest PA group.

Table 1. Comparison of risk for developing 13 types of cancer among individuals with higher (top 10%) vs. lower (bottom 10%) levels of leisure-time physical activity.
  
There are several mechanisms by which regular PA is hypothesized to decrease the risk of developing cancer. Lower levels of hormones such as insulin, adipokines, estrone, and estradiol have been observed in many studies that have used PA as an intervention. Decreased levels of inflammation and improved immune function are also seen among individuals who are physically active; these mechanisms are also thought to reduce cancer risk. Speedier passage of food through the gastrointestinal tract is seen in more active individuals, which is thought to decrease the risk of colon and other digestive cancers.   
 
A primary strength of this recent study is that it is the largest ever conducted in the area of PA and cancer. The 12 combined studies had a similar methodological approach, and the sheer number of cancer cases allowed better insight into the relationship between PA and less common cancers. The significantly increased risk of malignant melanoma in the highest PA group was thought to be due to increased sun exposure in this group; with a stronger relationship observed in high-UV areas. Increased use of sunscreen among highly active individuals would likely decrease this risk substantially.

To learn more about healthy eating, and risk of chronic disease, take our Nutrition for Health and Fitness course, which is offered live in Dallas as well as online. Along with health and fitness professionals, the general public is always welcome to attend any of our courses!