Peak Fitness Lowers Lung, Colorectal Cancer Risk

Kristin Jenkins

May 14, 2019

If you are a clinician in search of compelling evidence to convince sedentary patients — without or with cancer — to get away from their screens and into an exercise program, look no further.

Results from one of the most diverse retrospective cohort studies to date show that a high level of cardiorespiratory fitness (CRF) can reduce the risk of lung and colorectal cancer in some individuals.

The huge study involving more than 49,000 patients also looked at patients with cancer.

Reviewing data on participants in the Henry Ford Exercise Testing (FIT) Project in southeast Michigan from 1991 to 2009, researchers also found that participants with the highest CRF levels determined by treadmill stress testing had dramatically lower rates of all-cause mortality after a diagnosis of either lung or colorectal cancer.

The study, led by Catherine Handy Marshall, MD, of Johns Hopkins School of Medicine in Baltimore, Maryland, was published online May 6 in Cancer.

"The results of the current study support the idea that clinically obtained cardiac stress testing provides important additional information regarding cancer risk and mortality after cancer diagnosis in a general, clinically referred population," the authors write.

Marshall told Medscape Medical News that "clinicians should absolutely be supporting patients in improving fitness."

For the study, the investigators analyzed data from 49,143 consecutive adults (median age, 54 years) referred by their physicians for treadmill stress testing between 1991 and 2009.

CRF was measured as metabolic equivalents of task (METs) categorized in levels of <6 METs, 6 to 9 METs, 10 to 11 METs, and ≥12 METs. The highest average CRF fitness level was 9.7 METs for men and 8.1 METs for women.

Over a median follow-up of 7.7 years, participants with the highest METs (≥12) for cardiorespiratory conditioning had a 77% lower risk of incident lung cancer (hazard ratio [HR], 0.23; 95% confidence interval [CI], 0.14 - 0.36) than those who with lower CRF (<6 METs; P value for trend < .01).

Participants with the highest METs also had a 61% lower risk of colorectal cancer (HR, 0.39; 95% CI, 0.23 - 0.66; P for trend across fitness groups < .01).

Cancer patients also benefited. The study authors report that a high level of CRF fitness dramatically reduced the risk of subsequent death following a diagnosis of lung or colorectal cancer.

Out of 388 diagnosed with lung cancer, those with the highest levels of CRF prior to diagnosis had a 44% lower risk of all-cause mortality than less-fit peers (HR, 0.56; 95% CI, 0.32 - 1.00; P for trend < .01). The median time to diagnosis was 4.9 years.

In 220 cases of colorectal cancer diagnosed during followup, the reduction in mortality risk was even higher. Participants with the highest CRF measures prior to diagnosis had an 89% reduced risk of all-cause mortality compared with those with lower METs (HR, 0.11; 95% CI, 0.03 - 0.37; P for trend across fitness groups < .01). The median time to diagnosis was 3.6 years.

"Our findings are [from] one of the first, largest, and most diverse cohorts to look at the impact of fitness on cancer outcomes," said Marshall in a statement. 

A total of 46% of the FIT cohort was female, 29% of participants were black, and 1% were Hispanic.

These findings are consistent with previous reports in two smaller, all-male cohorts, the researchers point out. In those studies, high CRF was associated with a 55% to 61% lower risk of incident lung cancer and a 44% to 70% lower risk of incident colorectal cancer.

The FIT findings are also similar to earlier studies such as the Copenhagen Male Study. It showed a high pre-diagnostic CRF can reduce mortality risk after a diagnosis of cancer.

The authors note that CRF is a measure of peak energy expenditure that includes physical activity, genetics, age, and the overall functional health of organ systems.

"Compared with physical activity alone, CRF is a better predictor of cardiovascular disease and all-cause mortality and improves the risk classification of cardiovascular disease when added to traditional risk factors," they say.

As previously reported by Medscape Medical News, this study adds to the growing evidence that exercise plays a significant role in the prevention of cancer, and has benefits for those living with cancer. Even regular walking appears to lower all-cause mortality compared with inactivity.

Last spring, the Clinical Oncology Society of Australia (COSA) released a position paper on exercise recommending it be part of the standard of care for all patients with cancer.

Not for Everyone?

In the new study, subgroup analysis by sex and race mirrored most of the study findings. However, there was no evidence that a high level of fitness reduced the risk of colorectal cancer in female and/or black cohort participants.

This could be the result of the smaller sample sizes in these subgroups, the researchers say.

They point out that women have a lower overall incidence of colorectal cancer compared with men and tend to be diagnosed at a later age. Also, potential confounders such as menopausal status and the use of hormone therapy were not measured.

Similarly, the investigators note that black Americans have a higher overall incidence of colon cancer compared to white Americans, and "were not as well represented in our high fitness group."

The cohort's most fit participants tended to be younger and male, and to have a lower body mass index (BMI). They were also less likely to be smokers or to be taking aspirin or statins.

Factors that contribute to the apparent protective effect of fitness are currently under active investigation, the investigators note. These include improved respiratory function, decreased bowel transit time, better immune function, and reductions in systemic inflammation.

Marshall reported a financial relationship with Bristol-Myers Squibb for the current study, and relationships with McGraw-Hill and DAVA Oncology outside of the submitted work. A number of coauthors also disclosed financial relationships with industry.

Cancer. Published online May 6, 2019. Abstract

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