Friday March 6 2009
Regular exercise can reduce mortality as effectively as quitting smoking
“Men in their 50s who increase their exercise regime live more than two years longer than couch potatoes of the same age,” The Guardian reported. It said that men who do just three hours of sport or heavy gardening a week live 2.3 years longer than sedentary men, and a year longer than those who do moderate exercise.
This study followed 2,300 men around 50 years of age from the early 1970s until 2006. Men with higher levels of activity had lower overall mortality compared to less active men. Men who increased their activity from low to high also had lower mortality than the sedentary men. This research supports the idea that regular exercise and activity are beneficial. However, there are some limitations. The complex interaction of medical, psychosocial and lifestyle factors that govern lifespan cannot be encapsulated in the four, very broad, questions on physical activity that the men answered. It is not possible to assure people that simply doing the gardening in middle age will add an extra two years to their lives.
Where did the story come from?
Liisa Byberg and colleagues from Uppsala University and Karolinska Institutet, Sweden, carried out this research. The work was funded by the Swedish Research Council. The study was published in the peer-reviewed British Medical Journal.
What kind of scientific study was this?
This prospective cohort study investigated how physical activity in middle age affects risk of death. It also compared this effect on risk of death with that of quitting smoking. The participants were comprised of all men born between 1920 and 1924 and living in the municipality of Uppsala, Sweden in 1970. Of the 2,841 men who were asked, 2,322 (82%) aged 49-51 participated. Each participant completed a validated health survey, which asked the following questions:
- Do you spend most of your time reading, watching TV, going to the cinema or engaging in other, mostly sedentary, activities?
- Do you often go walking or cycling for pleasure?
- Do you engage in any active recreational sports or heavy gardening at least three hours every week?
- Do you regularly engage in hard physical training or competitive sport?
Those answering yes to question one were classed as having low activity; those answering yes to two as medium; and three and four were classed together as high activity.
The same survey was repeated when the cohort reached the average ages of 60, 70, 77 and 82, with the final survey taking place in 2006. The researchers looked at changes in physical activity between the first and second surveys and classed them as unchanged low (low or medium activity at both surveys), unchanged high (high activity at both surveys), decreased (high in survey 1, low or medium in survey 2), and increased (low or medium in survey 1, high in survey 2).
The researchers also looked at the men’s occupations, educational levels and socioeconomic groups from the 1970 and 1980 census; height, weight and BMI at the time of each survey; blood pressure and medications for it; cholesterol; presence of diabetes; smoking (current, former or never a smoker, and changes in habit between surveys); and alcohol consumption (abstainer, normal, or sustained alcohol dependence).
Medical and psychiatric diagnoses were detected through the national hospital discharge register, and deaths obtained through the Swedish National Population Register. Numbers diminished at each repeat survey due to death or lack of availability. At the final survey, only 23% of those who took part in the first survey were available.
What were the results of the study?
At the time of the first survey, 49% of men reported high activity, 36% reported medium activity, and 15% were sedentary. At the end of follow-up, 1,329 men, 60% of the cohort had died. By the end of the study, they had a total of 61,456 collective years of follow-up.
Mortality rate was calculated to be reduced by 22% with high-compared-to-medium activity, and by 32% with high-compared-to-low activity. Absolute mortality rates per 1,000 collective years of follow-up were 27.1 for low activity, 23.6 for medium, and 18.4 for high activity.
Men who increased physical activity between the first and second surveys still had a higher risk of mortality compared to those with unchanged levels of high physical activity. However, if this increase in activity was continued to the third survey, these men showed no difference in mortality from those who reported high physical activity in all the surveys.
Men who had increased their levels of activity had a significantly reduced mortality compared to the men who had low activity levels in all surveys. This reduced mortality risk was similar to the reduction in mortality seen from stopping smoking compared to continued smoking.
What interpretations did the researchers draw from these results?
The researchers conclude that an increase in physical activity in middle age is “eventually” followed by a reduction in mortality compared to sustained low levels of activity, and similar to those with sustained high levels of activity. They say that this effect is similar to that observed with smoking cessation.
What does the NHS Knowledge Service make of this study?
This Swedish research enrolled a large group of men in the early 1970s and followed them up to the present day. The study has strengths in its size and its use of reliable sources of data to follow-up the outcomes of all participants. The study found that men who sustained higher levels of activity throughout the study had lower overall mortality compared to those with lower activity levels. In addition, men who increased their activity from lower levels to higher levels during follow-up also had reduced mortality compared to those with sustained low activity.
This research supports the theory that regular exercise and activity contribute to a longer life. However, the news headlines have been simplistic in their interpretation. The study used four, very broad questions in order to group men into categories of physical activity. Heavy gardening was included in the third question, which was then classed as high activity.
This is likely to have led to considerable variation in the men’s responses, and the possibility that some of them were incorrectly categorised. Other variables that were assessed also used very broad categories, and these are also likely to include inaccuracies. Alcohol consumption, for example, was classified simply as “abstainer, normal or sustained alcohol dependence”.
The researchers also considered other possible factors that can contribute to health. However, a person’s health and lifespan are affected by a complex interplay of medical, psychological, social and lifestyle factors, which could not have been assessed in their entirety.
As study members chose their own activity levels and were not randomly allocated to a certain level of activity, it is not possible to say whether other factors (e.g. medical health) affected how much activity they performed. In addition, the study only assessed men, therefore the results cannot be automatically applied to women.
It is not possible to assure people that simply doing gardening in middle age will earn them an extra two years of life. However, regular exercise, in addition to a healthy diet, is widely considered to be beneficial to a healthy life.