This is the bottom line – how long you live. As I have banged on about in the previous blogs, I regard healthspan as more important that lifespan, but no-one want to die sooner than necessary. As the old question goes – “who wants to live to be 90?” The answer is “someone aged 89.”
There is no answer to the question “What is normal life expectancy?”. What is certain is that our population is nowhere near reaching it. The surprising fact until very recently is that, despite our thoroughly unhealthy lifestyles, we have seen a gradual increase in life span, though not necessarily duration of healthy life.
In the years between 1991 and 2014 average life expectancy for men rose from 73.6 years in 1991 to 79.4 in 2014. For women the figures were 79.0 to 83.1. This unexpected good news has recently hit the buffers with figures produced by Public Health England suggesting that the trend has now flatlined. Indeed the Faculty of Actuaries has calculated that at the age of 65, the life expectancy of a man has fallen by four months and that of a woman has fallen by a whole year. This will be good news for the pensions industry which will reap a reward of £27 billion in liabilities from company balance sheets. The same is true in the US where life expectancy fell in 2017 from 78.7 to 78.6. More importantly the duration of healthy life – health span – has been falling for several years while the years spent in poor health has increased. We should not be surprised – just read on.
Effect of exercise on lifespan
There are two ways of judging how much a person exercises:
- Assessing physical activity either by questionnaire or by direct observation. The former is biased by the individual’s tendency to exaggerate, driven by so-called “social desirability bias”, and almost always gives a much greater exercise estimate than is shown by direct measurement. Direct observation gives the most accurate measure of physical activity but has a number of problems – it is difficult to do, difficult to compare between exercise types, takes special equipment and is expensive, and it only gives a result which applies to the period of observation. We can all up our game when we know we are being watched.
- Measuring physical fitness. There is a direct relationship between amount of exercise taken and the physical fitness level but with wide variations. There are other variables which affect the relationship such as inherited characteristics. However this method has the strength of giving a measurement which does not depend upon the unreliable witness of the participants.
Exercise volume and longevity
The most dramatic examples of the association between amount of exercise taken and longevity has been found in groups of people who take regular vigorous exercise as a part of their daily life, be it either at work or at play. Professor Jerry Morris’s 1950s study compared the outcomes for London bus drivers with the outcomes for bus conductors. The model of the driver was sitting behind the wheel, unable to exercise and fuming at all those pesky motorists and taxi drivers. The conductors on the other hand were on their feet all day, skipping up and down the stairs and taking plenty of exercise. Sure enough the drivers had a higher mortality, largely due to a greater risk of coronary disease.
In those days the numbers of physically active workers was considerably greater than is the case nowadays – mechanisation has greatly reduced the role of occupation in making the working man take exercise. Morris repeated his findings in a comparison of the leisure time activities of civil servants. Those who exercised vigorously as part of their leisure activity fared much better than their sedentary colleagues. A very important finding was the presence of a threshold for the effect of exercise – it was only those taking vigorous exercise in their leisure time who benefitted. Lower levels of exercise did not prolong life. An approximate level for this threshold was 40 minutes exercise to a state of breathlessness three to four times per week.
These findings have been supported by the famous Framingham study which followed a large group of middle aged and older citizens in the US. For this cohort, moderate activity increased the length of life by 1.3 years in men and by 1.5 years in women. High levels of physical activity further increased these figures to 3.7 and 3.5 years respectively.
A study of 15,000 Olympic Medal winners gives another view. The medalists live about 3 years longer than the general population – irrespective of the colour of the medal! . A greater benefit is found for those involved in aerobic sport than in power events and the effect is also enhanced in those who maintained regular exercise after their days of Olympic glory – with an increase in life expectancy of up to five years.
More recent examples of the life prolonging effect of regular exercise have looked at those who take regular vigorous exercise as part of their sporting activities such as runners, cyclists and swimmers. One study reviewed 500 runners, aged 50–59 and compared them with age-matched and sex-matched controls. After 19 years, 15% of the runners but 34% of controls had died. A review of all the available evidence indicates that runners have a 30-45% reduced risk of premature mortality and live more than three years longer than non-runners. Increasing the time spent running and increasing the intensity are both related to benefit up to about 4 hours per week and a total dose of 50 MET-hours per week. Above this dose of exertion further benefit is doubtful and there might be a small reduction of benefit.
Does it just seem longer?
A much quoted criticism of the benefit of exercise is the cynical suggestion that the amount of time spent exercising is about the same as the increase in lifespan. In one study such cynicism is convincingly debunked. The authors calculate that every hour spent in exercise increases life span by seven hours!
Optimal exercise dose
Can you take too much exercise? Yes, you probably can. Most studies have found an increasing lifespan with increasing time spent in exercise, at least up to 300 minutes per week of vigorous exertion. However it is possible that higher levels may see a flattening off of benefit and even a reduction in lifespan for much greater doses.