Inactivity is “as deadly as smoking” reported the Daily Mail, describing how a lack of exercise is now causing as many deaths as smoking across the world.
The headline is based on a study published in the Lancet that estimates the burden of physical inactivity on global deaths and major diseases including coronary heart disease, type 2 diabetes and breast and colon cancer. Researchers estimate that lack of exercise could be responsible for around one in 10 cases of heart disease (10.5%) and just under one in five cases (18.7%) of colon cancer in the UK.
It estimated that overall, physical inactivity caused more than 5.3 million of the 57 million deaths that occurred worldwide in 2008. The researchers suggest this is equivalent to the 5 million deaths attributed to smoking in 2000 - a point that made the headlines. It is unclear whether these two estimates were based on studies with similar methods and so they may not be directly comparable.
Many of the headlines could be seen as misleading as smoking rates are lower than the number of inactive people in developed countries - this arguably making smoking more risky than being inactive. Still, this research provides an accurate assessment of the dangers to your health being physically inactive can bring.
Where did the story come from?
The study was carried out by a collaboration of international academic researchers on behalf of the Lancet Physical Activity Series Working Group. The report stated that the research received no direct funding.
The study was published in the peer-reviewed medical journal The Lancet, and is part of its wider series on physical activity (see “UK third ‘laziest’ country in Europe”).
Most of the media covered this story by focusing on the notion that physical inactivity was as bad as smoking or caused a similar amount of deaths. The study in question did not actually compare smoking and physical inactivity deaths directly but did mention this potential equivalence in the discussion section of the research (the section where research findings are placed in the context of other research).
To this degree the media reporting was generally fair, although few questioned to what extent this angle was actually true. Questioning statements such as this would be seen as good journalism as opposed to taking them at face value.
What kind of research was this?
This was an ecological study that aimed to estimate the effect of physical inactivity on health at a national and international level.
This type of study is useful to establish national and global patterns of physical activity and its influence on disease. However, the estimates of the impact of physical inactivity will only be as good as the information fed into these calculations, which could vary in quality from country to country.
The researchers stated that strong evidence shows physical inactivity increases the risk of many major adverse health conditions including:
- death (from any cause)
- coronary heart disease
- high blood pressure
- metabolic syndrome (including obesity and abnormal blood cholesterol levels)
- type 2 diabetes
- breast and colon cancer
Because a large proportion of the world’s population is inactive, this link is a major public health issue. The researchers aimed to quantify the effect of physical inactivity on these major conditions by estimating how much a disease could be prevented if inactive people were to become more active and to estimate the gain in life expectancy this could produce.
What did the research involve?
Researchers estimated the population attributable fraction (PAF), a measure used by epidemiologists to estimate the effect of a risk factor (in this case physical inactivity) on the incidence of disease in groups of people. PAF is also used to estimate the effect of reducing or removing such a risk factor. This gives policy makers an idea of how much disease could be prevented through efforts to reduce or remove different risk factors.
Researchers focused on coronary heart disease, type 2 diabetes, breast and colon cancer, and life expectancy.
Researchers defined physical inactivity as activity that failed to meet current World Health Organization (WHO) recommendations. The recommendations are split into different age groups:
- 5-17 years
- 18 to 64 years
- 65 years and above
For adults, these include the recommendation to do at least 150 minutes (2.5 hours) of moderate-intensity aerobic physical activity throughout the week, or at least 75 minutes of vigorous intensity activity, or a combination of the two. Physical activity included:
- leisure time physical activity
- walking or cycling
- household chores
- playing games and sports
The WHO also gathers data, by country, on the prevalence of physical activity in the population using two similar standardised questionnaires. This was one of the sources of data used in the study. They reported this data was robust for North America and Europe but less so for other countries.
To source more physical activity data, the researchers contacted several national cohort studies throughout the world, with particular emphasis on data outside of North America and Europe. For each study, data on physical activity was obtained alongside whether that same person went on to develop coronary heart disease, type 2 diabetes, or breast or colon cancer. Information on deaths was also obtained.
The researchers then pooled the data from different sources and calculated how much more likely people who were inactive were to die or develop these diseases compared to those who were active. Their final and appropriate analysis also estimated the effect on life expectancy of completely eliminating physical inactivity.
What were the basic results?
Worldwide, the researchers estimated that physical inactivity caused:
- 6% (ranging from 3.2% in southeast Asia to 7.8% in the eastern Mediterranean region) of coronary heart disease cases
- 7% (range 3.9% to 9.6%) of type 2 diabetes cases
- 10% (range 5.6% to 14.1%) of breast cancer cases
- 10% (range 5.7% to 13.8%) of colon cancer cases
- 9% (range 5.1% to 12.5%) of premature deaths (due to any cause) – this equates to more than 5.3 million of the 57 million deaths that occurred worldwide in 2008
The researchers estimated that if inactivity could be reduced by 10%, 533,000 deaths could be averted each year. If inactivity was reduced by 25% the estimate was that more than 1.3 million deaths could be avoided.
In the hypothetical scenario that physical inactivity was completely eliminated, the researchers estimated that global life expectancy would rise by 0.68 years (range 0.41 to .95 years).
While this may seem surprisingly low it does represent an average based on all the people in the world, both active and inactive. For perspective the researchers highlighted related research from the US showing that inactive people gained between 1.3 to 3.7 years from the age of 50 years by becoming active.
Looking at the UK data only, researchers estimated that inactivity caused:
- 10.5% (95% confidence interval 4.0% to 17.3%) of coronary heart disease
- 13.0% (6.4% to 20.2%) of type 2 diabetes
- 17.9% (17.9% to 27.8%) of breast cancer
- 18.7% (10.5% to 27.1%) of colon cancer, and
- 16.9% (13.6% to 20.3%) of deaths from any cause
How did the researchers interpret the results?
The researchers concluded that physical inactivity has a ‘major health effect worldwide’ and that a decrease or removal of this unhealthy behaviour could improve health ‘substantially’. In their discussion, they also state that, ‘these findings make inactivity similar to the established risk factors of smoking and obesity’.
Citing other research, they stated that smoking was estimated to cause approximately 5 million deaths worldwide in 2000 and that this is on the same magnitude as the 5.3 million deaths globally they had estimated were due to physical inactivity.
This ecological study estimated the global impact of physical inactivity and models the theoretical lives saved if physical inactivity levels were to be reduced across the globe.
This study serves to highlight the large and wide-ranging impact of physical inactivity on global disease levels and death. However, the following study limitations should be considered:
- Physical activity was based on self-reported physical activity levels, which can be misleading. The authors of the research say that this tends to underestimate differences between active and inactive people and so would underestimate the impact of physical inactivity globally. The researchers therefore concluded that their estimates ‘are likely to be very conservative’. Using a more objective measure of physical activity would address this issue above but may not be a practical way of obtaining such information.
- The same population attributable fraction (PAF) was used for all countries to estimate the impact of physical inactivity on disease and death. This PAF was largely based on North American and European data. This means it will have assumed that the impact of physical inactivity on death and disease was similar in all countries. It is unclear whether this assumption would be accurate across the globe in countries such as those with low incomes (developing countries).
- The researchers examined only major non-communicable diseases and deaths from any cause affected by physical activity. They did not assess other diseases affected by physical activity in this study and so the actual impact may be larger.
- Not all physically inactive people are inactive voluntarily, some may be physically incapable. The impact on life expectancy and deaths avoided due to the elimination of physical inactivity all together is not realistic. However, this is useful to stimulate debate.
- As it is an ecological study, it does not tell us much about variation among individuals within these countries, only national and global trends.
While smoking (an active harm) and inactivity (a passive harm) may kill similar number of people, smoking rates are lower than the number of inactive people, making smoking a more risky activity to the individual.Behind the Headlines on twitter*.