Inactivity, disability, and death are all interlinkedBMJ 2014; 348 doi: https://doi.org/10.1136/bmj.g2804 (Published 29 April 2014) Cite this as: BMJ 2014;348:g2804
- Elizabeth Badley, professor1
- 1Dalla Lana School of Public Health, University of Toronto, 155 College Street, Toronto, ON, Canada, M5S 1A8
- Correspondence to:
Physical activity has long been recognised as an important determinant of health and longevity, and many countries have explicit physical activity guidelines for promoting health.1 2 The corollary of this is that people who do not meet the guidelines, a substantial proportion of the population,3 are at risk of worse health. However, relatively little attention has been given to the question of how much activity is needed to make a difference. Although this is not explicitly their primary purpose, two new papers shed light on this question. Dunlop and colleagues (doi:10.1136/bmj.g2472) followed a cohort of people who had mild to moderate osteoarthritis or were at risk of osteoarthritis to look at the development of disability over two years.4 Cooper and colleagues (doi:10.1136/bmj.g2219) estimated the relation between physical capability in midlife—as indicated by grip strength, chair rise speed, and standing balance—and later mortality.5 Both showed that the relation between inactivity and risk of disability or death is not linear: people in the extreme lowest of the low categories for physical activity or capability were at disproportionately greatest risk.
Dunlop and colleagues’ study followed a cohort of older adults with a mean age in the early 60s for two years. Three quarters of their participants were overweight or obese. Physical activity was measured objectively using an accelerometer, and participants were assigned to one of two categories of activity: non-sedentary activity of light intensity and activity of moderate to vigorous intensity. This was a very sedentary cohort that averaged about 20 hours a day with no activity, and any activity reported was overwhelmingly in the light intensity category. Almost 15% of those in the lowest quarter of activity developed disability over two years, compared with well under 10% of those in the other three quarter groups. Although the development of disability could arguably be due to osteoarthritis, not all cohort members had symptoms, and the authors were able to control for other musculoskeletal symptoms and selected comorbidities including cancer and heart disease. The disproportionately high risk for the lowest quarter held when other predictors of disability and time spent in moderate to vigorous activity were controlled for.
The paper by Cooper looks at the physical capability of people aged 53 enrolled in the 1946 British birth cohort and relates this to mortality over the next 13 years. Trained nurses used a standard protocol to assess three physical capability measures—grip strength, chair rise speed, and standing balance time—and a composite measure was derived by combining the score on these measures. The mortality rate was more than five times higher for people in the lowest fifth of the composite score compared with those in the highest fifth. The excess risk was even higher for those who could not perform the individual measures at all. The relation still held after adjustment for other variables likely to be associated with mortality. As in Dunlop and colleagues’ study, the difference between the lowest and highest fifths was much greater than the difference between the highest and other fifths. Both sets of authors note that the excess risk in the lowest quarter or fifth may represent the influence of subclinical disease and the aging processes even in midlife, as well as lifetime exposure to physical activity, smoking, and an unhealthy diet.
A major limitation of Cooper and colleagues’ paper is that the specific health problems that prevented participants from being able to perform each test were not recorded. This deficit was remedied at a later follow-up examination of this cohort when, as expected, commonly reported reasons included diseases of the musculoskeletal system. Juxtaposing the two papers, lack of physical activity among adults with osteoarthritis (the most common type of arthritis6) is associated with the development of disability and likely associated reductions in physical capability.7 Reduced physical capacity in turn compromises life expectancy. In other words, more is at stake for inactive people with osteoarthritis than just an increased risk of disability. Mounting evidence shows that osteoarthritis is associated with increased mortality8; perhaps more thought needs to be given to the role of physical activity in this context.
Many of the previous studies on the relation between physical activity and disability or death have been confined to older adults.7 These new papers focus on people in the middle years of life and those with low activity or physical capacity levels. In both papers, although a gradient with increasing activity exists, the excess risk for disability or death in the lowest activity group is notable and suggests that this group should be a priority group for intervention. The good news is that increasing activity just a little could pay dividends. For example, on the basis of data from Dunlop and colleagues’ study, increasing light intensity activity by just over an hour a day might do the trick for people in the most inactive group. Among adults who watch a lot of television, for example, this might be achieved by moving around during commercial breaks. An underlying message of these papers is that every little helps.
Cite this as: BMJ 2014;348:g2804
Competing interests: I have read and understood the BMJ Group policy on declaration of interests and declare the following interests: none.
Provenance and peer review: Commissioned; not externally peer reviewed.
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