Cardiorespiratory Fitness Levels May Influence Cancer Risk in Men

Cardiorespiratory fitness (CRF) levels may play a role in reducing the risk of developing and dying from certain common cancers in men, a prospective cohort study from Sweden suggested.

Over a mean follow-up of 9.6 years among over 170,000 men, higher levels of CRF were associated with a significantly lower risk of incidence of colon (HR 0.98, 95% CI 0.96-0.98) and lung cancer (HR 0.98, 95% CI 0.96-0.99), and a higher risk of prostate cancer incidence (HR 1.01, 95% CI 1.00-1.01).

Importantly, higher CRF levels were also associated with a lower risk of death due to cancers of the colon (HR 0.98, 95% CI 0.96-1.00), lung (HR 0.97, 95% CI 0.95-0.99), and prostate (HR 0.95, 95% CI 0.93-0.97), reported Elin Ekblom-Bak, PhD, of the Swedish School of Sport and Health Sciences in Stockholm, and colleagues in JAMA Network Open.

"Because of the size of the sample, we were able to look at both the relationships between cardiorespiratory fitness and not only the risk of three of the most common cancers [in men], but also the risk of dying from these cancers," Ekblom-Bak explained to MedPage Today.

In fully adjusted models, the associations for colon cancer incidence remained for moderate (HR 0.72, 95% CI 0.53-0.96) and high (HR 0.63, 95% CI 0.41-0.98) levels of CRF, compared with very low CRF levels.

For lung cancer mortality, only high CRF (HR 0.41, 95% CI 0.17-0.99) was significant. Age modified the associations for lung cancer incidence (HR 0.99, 95% CI 0.99-0.99) and for death due to lung cancer (HR 0.99, 95% CI 0.99-0.99; P=0.04), where lower risks with higher CRF were noted only in participants ages 60 and older.

For prostate cancer mortality, associations remained for low (HR 0.67, 95% CI 0.45-1.00), moderate (HR 0.57, 95% CI 0.34-0.97), and high (HR 0.29, 95% CI 0.10-0.86) CRF levels. Age also modified the associations for prostate cancer incidence (HR 1.00, 95% CI 1.00-1.00; P<0.001), with a slightly higher risk among participants younger than 60 with increasing CRF.

We observed "strong, dose-response association between CRF and lower risk for prostate cancer mortality, even after adjustment for other important variables such as BMI and comorbidity," Ekblom-Bak said.

The association with prostate cancer incidence has been observed in other studies; "however, this counterintuitive relationship may be influenced by a tendency for men with higher CRF to better attend prostate cancer screening programs," she added.

Ekblom-Bak and team also pointed out that lifestyle factors may play less of a role in the incidence of prostate cancer due to its high heritability.

Previous research has shown that higher CRF levels are tied to lower all-cause mortality and death from cardiovascular disease and cancer.

"The importance of CRF could be included in future patient-doctor discussions and simple submaximal cycle tests could be included in health history assessments to better understand a person's risk profile based on their lifestyle choices and health status," Ekblom-Bak said, underscoring that "people should be informed of the benefits of not only increasing their physical activity but also CRF, and supported to find ways to improve their CRF in ways that feel best for them and avoids shaming the individual."

Anne McTiernan, MD, PhD, of the Fred Hutchinson Cancer Center in Seattle, said that while the study's findings were not new, it "had a larger number of men enrolled and followed for an average of almost 10 years, and therefore had greater ability to determine associations with cancer risk."

"A major issue is that not all individuals who exercise at high levels will experience improvements in cardiorespiratory fitness, as there is some genetic control to this measure," she pointed out. "While cardiorespiratory fitness levels are interesting data, they do not provide clear information on how much and what kind of exercise people should do to decrease cancer risk."

"Luckily, many excellent epidemiologic studies have looked at physical activity levels and risk for individual cancers in both women and men and have found that physical activity is associated with lower risk of many cancers," she added.

Ekblom-Bak and colleagues used the health profile assessment database, managed by the HPI Health Profile Institute, for men who had a first-time assessment, including a CRF assessment, from October 1982 to December 2019. Data on first-time cancer incidence and mortality came from the Swedish National Patient Registry and National Cause of Death Registry. CRF level, defined by maximal oxygen consumption, was assessed using a submaximal cycle ergometer test.

The researchers included 177,709 participants; mean age was 42, and mean body mass index (BMI) was 26. Mean age was 49 among those with very low CRF levels, and 35 among those with high CRF levels.

During follow-up, a total of 499 incident cases of colon cancer, 283 cases of lung cancer, and 1,918 cases of prostate cancer occurred, in addition to 152 deaths due to colon cancer, 207 due to lung cancer, and 141 due to prostate cancer.

Ekblom-Bak and co-authors noted that participation in the health profile assessment is voluntary, and only data on employed Swedes are collected. They also were not able to account for use of aspirin and statins when looking at colon cancer incidence, because of a lack of available data. In addition, the maximal oxygen consumption calculations used were estimates, which may have differed from true values.

McTiernan noted that the overall mortality findings were influenced by the high or low mortality rates of specific cancers.

"The applicability of the study to women and to persons of diverse race and ethnicity cannot be inferred," she added.

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