Physical activity is often advocated for improved health, and there’s a considerable body of evidence which supports this. For example, studies have linked regular physical activity and/or exercise with a reduced risk of chronic, life-threatening conditions including heart disease and type 2 diabetes. There has even been some research that has linked physical activity with reduced risk of death. However, there is relatively little evidence on what effect changing exercise habits appears to have on risk of death. This sort of evidence is important, as it can help to determine whether, say, upping activity levels has real benefits for health.
A research paper published in this week’s British Medical Journal helps inform us regarding the potential for exercise to reduce risk of death. In this study, more than 2200 Swedish men were assessed between the ages of 50 to age 82. Physical activity levels (as well as other parameters) were assessed at ages 50, 60, 70, 77 and 82 [1]. At each point, activity levels were gauged via a questionnaire, which put men into one of three categories:
Low activity: Men spending most of their time reading, watching TV, going to the cinema, or engaging in other, mostly sedentary activities.
Moderate activity: Men who often go walking or cycling for pleasure.
High activity: Men engaging in any active recreational sports or heavy gardening for at least 3 hours every week, and/or who regularly engage in hard physical training or competitive sport.
The relationship between activity levels and overall risk of death was assessed throughout the study. Some of the analysis accounting for so-called confounding factors such as blood pressure, smoking, presence of diabetes and weight. This helped to determine the impact of exercise habits, and not other factors associated with this lifestyle habit, with risk of death.
Here are some of the most important findings from this study:
Mortality rates in individuals engaging in high levels of activity were lower than those in men engaging in medium levels of activity. Mortality rates in individuals engaging in medium levels of activity were lower than those in men engaging in low levels of activity.
Compared to low levels of activity, high levels of exercise were associated with a 32 per cent reduced risk of death.
Compared to medium levels of activity, high levels of exercise were associated with a 22 per cent reduced risk of death.
Men who increased their level of physical activity between the ages of 50 and 60 appeared not to reap the benefits of this in terms of reduced mortality for some years.
However, after 10 years of increasing activity levels, risk of death was essentially the same as men who had had high levels of physical activity throughout the study.
After 10 years, increasing physical activity to a high level was associated with a rough halving in the risk of death.
This compares favourably with the apparent reduction in mortality seen in men who stopped smoking (a reduction of about 40 per cent).
After adjusting for confounding factors, compared to low levels of activity, high levels and medium levels of activity were associated with an additional 2.3 and 1.1 years in life expectancy.
What this study suggests is that exercise really is associated with reduced risk of death and improved life expectancy. Moreover, taking up high levels of activity in middle-age does seem to confer benefits in terms of reduced risk of death, though on average it takes about 10 years for the benefits are realised.
If we assume the 2.3 years in life expectancy associated with high levels of activity is correct, we can do a calculation around the ‘return on investment’ regarding time spent exercising. Let’s assume someone aged 50 who is sedentary starts to exercise for a total of 3 hours per week and eventually dies in his mid-80s. He will have spent about 5,000 hours exercising during his life. Let’s say, though, that he gained additional years because of the exercise. This equates to about an additional 20,000 hours of life. In other words, each hour of time spent exercising appears to return four additional hours of life. This seems like a good use of someone’s time, and that’s particularly the case if the chosen activity is something enjoyable and/or sociable.
References:
1. Byberg L, et al. Total mortality after changes in leisure time physical activity in 50 year old men: 35 year follow-up of population based cohort. BMJ 2009;338:b688
but what if people are in the ‘very active’ camp because their underlying health was better in the first place, and that’s the reason for the longevity, not the exercise itself?