Cardiorespiratory fitness and death from cancer: a 42-year follow-up from the Copenhagen Male Study

Introduction

A well-known relationship between cardiorespiratory fitness (CRF) and cardiovascular disease 1 exists. The relationship between CRF and cancer mortality, however, has been less studied and is more uncertain. CRF is an expression of maximal oxygen uptake per kilogram body weight and reflects maximal metabolic ability. The current knowledge concerning the relationship between physical activity and health has been generated from epidemiological studies from the 1950s up to the present day. 2 3

During the last decades, there has been an increased interest in the relationship between CRF and the development of cancer. There appears to be a consistent relationship between a high CRF level and lower risk of cancer across cancer types, 4-8 except for prostate cancer and certain other cancers. 5 9 10 Many cancers often take decades to develop from subclinical states to manifest disease. Subclinical cancer may therefore be present at the time of CRF assessment and may lead to confounding of the findings if follow-up time is short: Thus, it may be that subjects with subclinical disease have a lower physical performance and subsequently are at increased risk of dying from cancer, resulting in the observed association. The relationship between CRF and death from cancer with a very long time of follow-up may be advantageous in order to account for this potential bias. 11

In the present study, we hypothesised that CRF (maximal oxygen consumption (VO₂max)), assessed from a bicycle ergometer test, was inversely associated with death from cancer and all-cause mortality among 5131 middle-aged men free from cancer at baseline and followed for 42 years for cancer mortality and 44 years for all-cause mortality. The long follow-up time allowed us furthermore to investigate the association between CRF and outcome after excluding subjects dying within 2 decades of study inclusion, thereby minimising the possibility that poor health might confound the findings between CRF and death from cancer.

Methods

The Copenhagen Male Study

The Copenhagen Male Study was established in 1970-1971 as a prospective study of middle-aged men employed at 14 large workplaces in Copenhagen. 12 All men were interviewed by a physician (FG) and underwent estimation of physical fitness (VO₂max). Physical fitness was determined using information on heart rate and work load from a bicycle ergometer...