Cardiorespiratory fitness and BMI measured in youth and 5-year mortality after site-specific cancer diagnoses in men-A population-based cohort study with register linkage.

Background: Our aim was to assess associations between cardiorespiratory fitness (CRF) and body mass index (BMI) in youth and 5-year mortality after site-specific cancer diagnoses in men.

Methods: Men with cancer from a population who underwent military conscription at ages 16-25 during 1968-2005 in Sweden were included. CRF was assessed as maximal aerobic workload on a cycle ergometer test and was classified as low, moderate, or high. BMI (kg/m ) was classified as underweight (<18.5), normal weight (18.5-24.9), overweight (25-29.9), or obesity (>30). Conscription data were linked with register data on cancer diagnosis and mortality. Analyses included CRF, BMI, date of diagnosis, and age, year, and center for conscription.

Results: A total of 84,621 cancer cases were included. Mean age at diagnosis was 52 years. Follow-up data were available during a mean of 6.5 years. There were linear protective associations between CRF and mortality after any cancer diagnosis (hazard ratio [HR] for high vs. low CRF 0.70), malignant skin cancer (HR 0.80), non-Hodgkin lymphoma (HR 0.78), and cancer in the lungs (HR 0.80), head and neck (HR 0.68), pancreas (HR 0.83), stomach (HR 0.78), liver (HR 0.84), rectum (HR 0.79), and bladder (HR 0.71). Overweight and/or obesity were associated with increased mortality after any cancer (HR for obesity vs. normal weight 1.89), malignant skin cancer (HR 2.03), Hodgkin lymphoma (HR 2.86) and cancer in the head and neck (HR 1.38), thyroid (HR 3.04), rectum (HR 1.53), kidney (HR 1.90), bladder (HR 2.10), and prostate (HR 2.44).

Conclusion: We report dose-dependent associations between CRF and BMI in youth and mortality after site-specific cancer diagnoses in men. The associations with mortality could be due to both cancer inhibition and an improved tolerance to withstand cancer treatment. These results strengthen the incentive for public health efforts aimed at establishing a high CRF and normal weight in youth.