A recent study published in the British Journal of Sports Medicine assessed the association between cardiorespiratory fitness (CRF) and some site-specific cancers in healthy young men.
Studies have shown that CRF is associated with a reduction in the risk of developing certain types of cancers. However, large-scale studies of the link between CRF and multiple cancer sites have been sparse.
In the present study, researchers demonstrated a linear association between CRF and a reduced risk of developing most types of cancers investigated. This includes certain types of cancers that have not been previously linked to CRF or physical activity. These results emphasize the need for interventions to increase physical activity and CRF in youth.
What did the researchers do?
The study cohort comprised young Swedish men enlisted in the military between 1968 and 2005. Participants diagnosed with cancer before or within five years of military conscription and those who died or emigrated within five years after military conscription were excluded from the study. None of the study participants had any underlying health conditions or injuries.
The height, weight, and body mass index of the participants were measured; those who weighed <18.5 kg/m2 were categorized as underweight, between 18.5 and 24.9 kg/m2 as normal weight, between 25 and 29.9 kg/m2 as overweight, and ≥30 kg/m2 as obese. Information regarding the level of parental education was obtained from Statistics Sweden and grouped according to the highest level of education of either parent.
CRF was estimated using the maximal aerobic workload cycle test during conscription. The researchers used Cox regression models to assess linear relationships and included factors such as age, body mass index, CRF, year and site of conscription, and parental education level. For easier interpretation, CRF was categorized into low, moderate, and high, and the results comparing individuals with low and high CRF were reported.
A total of 1,078,000 men were included in the primary analyses, among whom 84,117 (7%) developed cancer in at least one site over a 33-year follow-up period. Participants in the low, moderate, and high CRF groups showed similarities in blood pressure and age at conscription.
However, those in the low CRF group were found to be more likely to be obese compared to those in the high CRF group. Additionally, individuals in the low CRF group had a higher likelihood of reporting alcohol and substance abuse and lower parental education compared to those with greater CRF.
Sixty percent (n=21,307) of those enlisted in the military between 1968 and 1970 reported current smoking habits. Notably, those who had greater CRF reported lower active smoking; i.e., 67% of individuals with low CRF, 59% with moderate CRF, and 44% with high CRF reported smoking. In contrast, among those conscripted between 2002 and 2005, only 7% reported current smoking.
Linear associations were observed between higher CRF and a lower risk of developing cancer in various sites, including the head and neck (n=2,738), stomach (n=902), esophagus (n=689), pancreas (n=1,280), rectum (n=2,337), colon (n=3,222), liver (n=1,111), lung (n=1,635), and kidney (n=1,753).
However, increased CRF was associated with a higher risk of malignant skin cancer (n=23,064) and prostate cancer (n=14,232).
While the researchers did not observe any association between CRF and the risk of developing hematological cancers such as leukemia or Hodgkin’s/non-Hodgkin’s lymphomas, there was a weak association between higher CRF and a higher myeloma risk, which was not confirmed in supplementary analyses.
Linear associations were detected between CRF and the risk of developing any cancer in the primary analyses, but no such association was observed in the supplementary analyses. No associations were detected between CRF and the risk of cancer development in the thyroid and the central nervous system.
According to these findings, higher fitness levels in young men are directly associated with a lower risk of developing 9 out of the 18 site-specific cancers investigated in this study, with the most significant risk reduction of 21% observed in the gastrointestinal tract.
To sum up, the study's findings revealed several associations between decreased risk of developing some site-specific cancers and increased CRF in healthy youth. They show that increased physical activity and CRF may lead to long-term health benefits in young men by decreasing the risk of some types of cancer.
Furthermore, they highlight the significance of regular physical activity and healthy fitness levels to decrease the risk of developing many site-specific cancers and other diseases. These results inform public health policymaking and underscore the importance of promoting health and fitness in young men by increasing physical activity and improving CRF.