Exercise and longevity Part 2

Last week I talked about the connection between exercise “volume” and length of life. A bit more on this:

 ^{What sort of exercise?}
Aerobic exercise is more effective for prolonging life than muscle strengthening, but a combination of the two has the greatest effect. There is some evidence that regular swimming may be even more effective in postponing mortality, provided that possible hazards are avoided (see above)..

The mode of commuting to work is relevant. A study of more than half a million adults aged 40–69, followed up for five years, found that those who cycled to work had about half the risk of dying during this time as those who used public transport.

Can it be too late to start?

Most of the epidemiological studies described last week involve long-term exercisers who have been at it for most of their adult lives. Is it ever too late to start? The answer is a qualified no, because the effect on longevity takes a while to kick in. It probably takes about 10 years of high levels of activity to increase longevity. A cohort of more than 315,000 Americans aged 50–71 had their exercise habits tracked and were followed up for 20 years. Unsurprisingly, the mortality during follow-up was about 35 per cent lower in the habitually active group than in those who took little exercise. Surprising, however, was the finding that those who took up exercise later in life and then maintained it ultimately had a similar reduction in mortality. As The Times reported, ‘It is never too late to get off the sofa and extend your life.’

Why does exercise prolong life?

Regular exercise, as we have seen, reduces the risk of a number of non-communicable diseases and this must largely explain its effect on life expectancy. However, there other intriguing contributors, including an effect on cellular ageing. DNA is the genetic chromosome-carrying material found in all the cells in our bodies. Telomeres are the caps on the end of each strand of DNA and they protect the DNA from damage each time a cell reproduces itself. With time and repeated cell division, the telomeres become shortened and may indeed become so short that they can no longer protect the DNA, with subsequent cellular disruption. Telomere length is thus allied to cellular age and represents our biological age rather than our chronological age. Regular exercise has an effect on telomere length. There is a positive and significant relationship between cardiorespiratory fitness and telomere length, most marked in middle-aged and older people, which emphasises the importance of cardiorespiratory fitness for healthy ageing. The reduction in cellular aging has been found to be about nine years in very active older people.

Physical fitness and longevity

There is a clear relationship between increasing habitual exercise and increasing physical fitness. For instance, running: every 30 minutes of running per week is associated with 0.5 MET higher fitness level. Numerous studies have confirmed the relationship between physical fitness and life expectancy – indeed physical fitness in middle age is the best predictor bar none of what age you will achieve, and that includes blood cholesterol, presence of obesity, high blood pressure, diabetes or even pre-existing heart disease, and cigarette smoking. Only your current age is a better predictor of how many years are left to you. The reduction in mortality in the fit compared with the unfit is largely due to lower rates of cardiovascular disease and cancer.

A summary of the results of 33 studies that compared physical fitness and mortality was published in 2009. The population included over 100,000 people without heart disease, diabetes, high blood pressure or high blood cholesterol. The subjects had all had an initial exercise test to measure their fitness and were then followed for a mean of 11 years. Fitness was expressed in metabolic equivalents – METs (1 MET being the energy expenditure at rest or 3.5ml/min/kg) and divided into three categories – low fitness being less than 7.9 METs (VO₂ = 27.6 ml/min/kg), intermediate fitness between 7.9 and 10.6 METs (27.6–37.1 ml/min/kg) and high fitness above 10.7 METs (37.4 ml/min/kg). There was a clear correlation between low fitness level and mortality – the risk of dying being 70 per cent higher in the low fitness group than in the high fitness group. Moreover, for every 1 MET increase in fitness (equivalent to an increase in walk/jog speed of 1km per hour) there was a 13 per cent decrease in the risk of dying. A similar study in 2015 found that the effect of fitness was even greater than this for younger age groups, with an 18 per cent lower mortality rate per 1 MET increase in fitness for those aged under 40, compared to the 12 per cent figure for those aged over 70. A study from Cleveland, Ohio, tested the relationship between physical fitness and mortality in 122,000 people followed up for an average of eight years after a treadmill test. The relationship was stark, with cardiorespiratory fitness being related to lower mortality over the period of study. This was most obvious in those with the very highest levels of fitness – these individuals had just one fifth the risk of dying than the least fit. The greatest benefit between being fit and being very fit was found in the over-70s, confirming the effectiveness and importance of exercise in older people.

Just how important is physical fitness?

I will expand on this next week –  just watch this space!