101 Facts About Ageing #42: Cardiorespiratory Fitness And Mortality

As Daniel Patrick Moynihan, an American sociologist, politician, and diplomat once said: “Everyone is entitled to his own opinion, but not his own facts”. And we wholeheartedly agree. A shared set of facts is the first step to building a better world with longevity for all. In that spirit, we are creating a series that covers 101 indisputable facts about ageing, health and longevity.

Cardiorespiratory fitness can be gauged by measuring the body’s maximum ability to utilise oxygen during exercise – if you make a person work harder and harder, they will eventually reach a point of maximum oxygen consumption. This rate is limited by their cardiorespiratory fitness – factors like how much oxygen is reaching the alveoli in the lungs, the total surface area of the alveoli over which oxygen can enter the blood, how quickly the heart can deliver that blood to the muscles, and how quickly the muscles can utilise that oxygen.

Cardiorespiratory fitness as measured by maximum oxygen utilisation is strongly correlated with reduced risk of mortality. In this study, 122 000 participants with an average age of 53 were divided into groups according to their maximum oxygen utilisation: the bottom 25% of people were considered low fitness; the 25th to 50th percentile were below average; the 50th to 75th percentile were above average; the 75th to 95th percentile were high fitness; to top 5% were considered ‘elite’. They were then followed for a median time of 8.4 years, and mortality between the groups was compared, controlling for factors like age, sex, body mass index, smoking, medication and disease history.

The above graph shows how a person’s hazard ratio (the relative probability of death compared to a baseline risk, in this case the risk associated with being in the ‘low’ category) changes depending on their cardiorespiratory fitness. Those who are in the below average category are around half as likely to die within the decade as those who are in the low category; being above average makes you around 70% less likely to die compared with the low category, and benefits continue all the way up to elite, albeit with diminishing returns.

The above table shows the increase in hazard ration due to smoking and prevalent chronic diseases compared with the increased hazard ratio from reduced cardiorespiratory fitness. Being below average fitness correlates with a 41% increase in mortality compared with above average fitness – roughly equivalent to being a smoker. The difference between low fitness and above average fitness is roughly the equivalent to the mortality increase from having end stage renal disease – nearly 280%.

These relationships are all associations and not necessarily causations, and so it is possible that some of these effects are due to other factors not directly related to exercise – for example, it is likely that those who achieve cardiorespiratory fitness through regular exercise also engage in other healthy practices. We can at the very least say that cardiorespiratory fitness is a strongly associated with longevity.