As per the Cancer Statistics 2018, one in three Americans will be diagnosed with an invasive cancer over their lifetimes. The number of cancer survivors is expected to exceed 20 million by 2026 as per the Cancer Treatment and Survivorship statistics 2016.
Decades of epidemiologic research have identified a physically active lifestyle as protective against the occurrence of some common cancers. A comprehensive review was conducted by the Department of Health and human services 2018 Physical Activity Guidelines Advisory Committee (PAGAC) to further investigate the effect of physical activity on the primary prevention of cancer.
Methodology
Studies were searched using PubMed, Cochrane, and CINAHL databases through December 2016 and were considered potentially eligible if they were:
- Systematic reviews
- Meta-analyses
- Pooled analyses published in English
- Investigated the relationship between all types and intensities of physical activity (PA) and the risk of invasive cancer of any type in adults.
- Relationship between all types and intensities of PA and mortality in persons of any age with a diagnosis of cancer.
An updated systematic literature search was conducted for the inclusive dates January 2016 through February 2018 with the same search words and design for cancer specific systematic reviews/meta-analyses.
Results
For 2018 Scientific Report,
- 45 systematic reviews, meta-analyses, or pooled analyses were reviewed to find an association between PA and cancer risk.
- 18 systematic reviews, meta-analyses, or pooled analyses were reviewed to find an association between PA and cancer survival.
For updated research,
- 5 out of 145 systematic reviews, meta-analyses, or pooled analyses were identified as relevant to be included in the report.
- In addition, the findings of 25 out of 1256 original source articles were included in the report.
In the research included, PA was measured by self-report with different types of PA questionnaires. The questionnaires inquired about participants' frequency and duration of involvement in several forms of PAs like walking, running, biking, recreational activities, and occupational or household activities. “The cut points for highest versus lowest activity levels varied across studies.
Strong evidence supporting reduced risk of bladder, breast, colon, endometrial, esophageal adenocarcinoma, renal, and gastric cancers with relative risk reductions from approximately 10% to 20% was found in individuals having high versus low levels of PA.
Cancer location | Number of studies reviewed/included for 2018 Scientific report (A) | Results (A) | Number of studies included in updated search (B) | Results (B) |
Bladder | 2 meta-analyses/systemic reviews and 1 pooled analysis | Cancer risk was significantly lower for individuals engaging in highest versus lowest categories of recreational or occupational PA level | No new research was identified in updated search |
|
Breast | 4 meta-analyses/systematic reviews and 2 pooled analyses | Reduced risk of breast cancer in highest level of all types of PA versus lowest amounts of all types of PA. Similar findings seen in pre- and post-menopausal women. | 2 meta-analyses | Reduced risk of breast cancer in highest level of all types of PA versus lowest amounts of all types of PA.
|
Colon | 8 meta-analyses/systematic reviews and 1 pooled analysis | Cancer risk significantly reduced for individuals engaged in highest versus lowest levels of PA | 2 meta-analyses and 3 original research reports of cohort studies (not included in any already reviewed meta-analysis or systematic reviews for colon cancer) | High versus low levels of PA decreased the risk of colon cancer. |
Endometrium | 4 meta-analyses and 1 pooled analysis | Cancer risk significantly reduced for individuals engaged in highest versus lowest levels of PA | 2 cohort studies | High versus low levels of PA decreased the risk of endometrial cancer. |
Esophagus | 3 meta-analyses/systematic reviews and 1 pooled analysis | Risk of esophageal adenocarcinoma statistically significantly reduced in individuals with high versus lowest levels of PA. No correlation was found between levels of PA and squamous cell carcinoma. | No new research was identified in updated search |
|
Gastric | 5 meta-analyses and 1 pooled analysis | Cancer risk significantly reduced for individuals engaged in highest versus lowest levels of PA | No new research was identified in updated search |
|
Renal | 1 meta-analyses and 1 pooled analysis | Cancer risk significantly lower for individuals engaged in highest versus lowest levels of PA | No new research was identified in updated search |
|
Lung | 6 meta-analyses and 1 pooled analysis | 25% relative reduction in lung cancer risk with highest versus lowest levels of PA | 2 cohort studies | No significant association was found between lung cancer risk and PA |
Prostate | 1 meta-analysis focusing on dose-response effects | No association between PA and local or advanced prostate cancer | 2 cohort studies | One found statistically significant association between PA and cancer risk and another observed statistically significant risk reduction only in advanced prostate cancer in active versus inactive men. |
All the PAs in all studies focused on aerobic activity.
Not enough evidence was available to find an association between hematologic, head and neck, ovarian, pancreatic, and prostate cancers and PA.
Body weight influenced the association between PA and risk of breast, endometrial, lung, ovarian, thyroid, and possibly oesophageal adenocarcinoma. Little information was available on differences in PA on cancer risk by age socioeconomic status, ethnicity or gender.
Results of the literature review included in the 2018 Scientific report on the relationship between PA and mortality among breast, colorectal and prostate cancers (post-diagnosis) showed an inverse association between amounts of PA and cancer-specific and all-cause mortality in survivors.
Takeaways
- Strong evidence was found supporting PA reducing the risk of breast, colon, endometrium, bladder, stomach, esophagus and kidney cancer.
- Moderate evidence was found supporting the association of higher levels of PA reducing lung cancer risk.
- Strong evidence was found supporting the association of higher levels of PA reducing cancer-related and all-cause-related mortality post-diagnosis of breast, colorectal, and prostate cancers.
Limitations
- Data from epidemiologic studies lacked clinical trial evidence in preventing cancer or improving cancer survival after getting diagnosed.
- Most studies did not control adequately for treatment type or completion, nor for undiagnosed disease progression which may have influenced the level of PA.
- Physical activity level couldn`t be determined at which risk reduction could be ascertained. A lower threshold of PA below which no benefits were evident couldn`t be determined.
- Data in meta-analyses was inconsistent and unable to determine the exact nature of the PA-cancer relationship by age, race, socio-economic status, or weight.
- Questionnaires used in studies are subject to recall error and reporting bias.
The PAGAC recommends future research in
- associations of physical activity on risk for specific cancers that have not been adequately studied.
- effects of physical activity on risk of cancer in specific age, racial, ethnic, and socioeconomic groups.
- Defining dose-response relationship to develop physical activity guidelines for cancer prevention.
- Determine the effects of specific types of physical activity on cancer risk and survival.
- Randomized controlled clinical trials testing exercise effects on cancer incidence are recommended to reduce confounding and errors in testing.
- For cancer survivors, long-term follow-ups with self-report or device-based measures of PA to determine association with recurrence or survival is recommended.
Source: Medicine & Science in Sports & Exercise Journal; American College of Sports Medicine, June 2019.
(https://journals.lww.com/acsm-msse/Fulltext/2019/06000/Physical_Activity_in_Cancer_Prevention_and.20.aspx)
