Every step you take
BMJ 2019; 366 doi: https://doi.org/10.1136/bmj.l5051 (Published 21 August 2019) Cite this as: BMJ 2019;366:l5051Linked research
Dose-response associations between accelerometry measured physical activity and sedentary time and all cause mortality
Linked opinion
“Sit less—move more and more often”: all physical activity is beneficial for longevity
All rapid responses
We are grateful for Dr Johnson’s interest in our recent paper examining the dose-response associations between sedentary time or physical activity and all-cause mortality published in The BMJ (1).
We agree with Dr Johnson (2) that our sample including eight cohorts may not be representative of the physical activity levels in the four countries they represent. However, three of the included cohorts -- NNPAS (Norway), NHANES (US) and ABC (Sweden) – comprised nationally representative samples with generally higher levels of physical activity and younger age, compared with the other non-representative, older cohorts. Reassuringly, the results on the associations of sedentary time and physical activity with mortality from only the three populations that included representative samples were similar to those from the overall meta-analyses (please see Supplementary Figure 1).
We also agree it would be of great interest to examine the associations between device-measured sedentary time or physical activity and with mortality in younger cohorts. Unfortunately, such data are currently unavailable. As further suggested by Dr Johnson (2) we aim to replicate our previous findings (3) examining the joint associations between sedentary time and physical activity with mortality in the current data set.
Finally, we wholeheartedly agree about the importance of light intensity physical activity in those who find it difficult to conduct physical activity of moderate intensity. Our results suggest the greatest magnitude of risk reduction for death was observed for total physical activity regardless of intensity, with an approximately fivefold difference in absolute death rate between the least and most active quarters. Thus, a simple public health message may be ‘sit less, move more and more often’.
References
1. Ekelund U, Tarp J, Steene-Johannessen J, Hansen BH, Jefferis B, Fagerland MW, et al. Dose-response associations between accelerometry measured physical activity and sedentary time and all cause mortality: systematic review and harmonised meta-analysis. BMJ [Internet]. 2019 Aug 21;l4570. Available from: http://www.bmj.com/lookup/doi/10.1136/bmj.l4570
2. Johnson LR. Move for life. BMJ 2019;366:l5051
Competing interests: No competing interests
Sir,
The article by Ekelund et al provides interesting insights into the relationship between physical activity, sedentary behaviour, and mortality.(1) One of the strengths of their research is the use of objective measures of physical activity and sedentary behaviour, in contrast to self-reported physical activity.(1,2) Their findings indicate a non-linear dose-response between all levels of physical activity and mortality, with low light intensity physical activity showing a consistent decline over time. In contrast, the reduction in mortality for all other levels of physical activity declines up to a threshold, then either plateaus, or increases. The reverse is true of sedentary behaviour, with greater sedentary behaviour associated with greater risk of mortality. These findings support guidance on physical activity issued by the World Health Organization (WHO).(3,4)
However, there are some concerns with respect to the research.
First, over 70% of subjects were female. Globally, women are less physically active than men across ages.(4) Therefore, the physical activity levels obtained from subjects are less likely to be representative of the general population, even in the USA and Scandinavian countries (where most of the studies were conducted).
Next, the subjects were on average 62.6 years old, by which time most individuals experience considerable musculoskeletal morbidity. This would adversely affect physical activity levels, and potentially increase sedentary behaviour. The authors state that what is classified as low-intensity physical activity might actually constitute moderate-vigorous physical activity for some subjects- perhaps an acknowledgement of their decreased physical ability to engage in physical activity. This also explains the paucity of readings that fell in the moderate-vigorous physical activity range.
Nevertheless, the findings bolster efforts to encourage any physical activity and decrease sedentary behaviour. However, similar research on younger individuals, and more representative samples is required. It would have been interesting to examine if the data supported findings from another study where one hour of physical activity mitigated the effects of sedentary behaviour.(5)
Given the propensity of physically inactive individuals to defer physical activity, it is heartening to note that this research provides evidence of all-cause mortality declining with increased duration of even low light-intensity physical activity. Such activity can be performed by most individuals without difficulty, and should be encouraged by clinicians and public health professionals alike. Moreover, the simplest of these activities - walking - does not require any equipment, and can be performed safely both outdoors and indoors. Since the evidence does not support a minimum duration of 10 minutes for physical activity, individuals could engage in brief activities multiple times in a day.(1) Slogans such as ‘Move for Life’, ‘Walk for 30’ and ‘Sitting is the new smoking’ could help reinforce research evidence in the general public.(3)
References:
1. Ekelund U, Tarp J, Steene-Johannessen J, Hansen BH, Jefferis B, Fagerland MW, et al. Dose-response associations between accelerometry measured physical activity and sedentary time and all cause mortality: systematic review and harmonised meta-analysis. BMJ [Internet]. 2019 Aug 21;l4570. Available from: http://www.bmj.com/lookup/doi/10.1136/bmj.l4570
2. Roopesh Johnson L, Prabha CC, Prakash D, Vasantha DG, Mohandas G, Reghunath K, et al. Pattern of And Risk Factors For Physical Activity Among Medical Students In A Private Institution. Natl J Res Community Med [Internet]. 2018 Jul 31;7(2):223. Available from: http://commedjournal.in/article/Volume7Issue3Jul-Sep2018/fulltext/16NJRC...
3. Johnson LR. Current physical activity guidance is misinterpreted. BMJ [Internet]. 2016 Sep 14;354(September):i4811. Available from: http://www.bmj.com/lookup/doi/10.1136/bmj.i4811
4. World Health Organization. WHO Fact sheet on Physical activity [Internet]. 2018 [cited 2019 Aug 28]. Available from: http://www.who.int/en/news-room/fact-sheets/detail/physical-activity
5. Ekelund U, Steene-Johannessen J, Brown WJ, Fagerland MW, Owen N, Powell KE, et al. Does physical activity attenuate, or even eliminate, the detrimental association of sitting time with mortality? A harmonised meta-analysis of data from more than 1 million men and women. Lancet [Internet]. 2016 Sep;388(10051):1302–10. Available from: http://dx.doi.org/10.1016/S0140-6736(16)30370-1
Competing interests: No competing interests
I read with interest your systematic review and meta-analysis on the Dose-response associations between accelerometry measured physical activity and sedentary time and all cause mortality and associated editorials (1). However I am disappointed that the main suggestion to improve activity in the population is to advise GPs to prescribe exercise.
This study demonstrates that activity should be part of our life regularly throughout everyday. The only way to achieve this is to design it into our life, changing the design of buildings, cities and neighbourhoods so movement is the first choice over passive transport like lifts, cars and public transport.
Evaluation of the London “Mini-Holland” projects (2) demonstrated that simple changes in the street layout led to the mid-point estimate active travel (walking plus cycling) time increased by 41.0 min (95% CI 7.0, 75.0 min) per week of study participants in the intervention area compared to controls.
To reduce the inactivity epidemic plaguing our patients, health professionals must take action to ensure our society is designed for activity. Individual health professionals and NHS organisations should be vocally supporting their local “living streets” and cycling campaign groups.
1) Klenk J, Kerse N. Every step you take. BMJ 2019; 366.
2) Aldred R, Goodman A. Impacts of an active travel intervention with a cycling focus in a suburban context: One-year findings from an evaluation of London’s in-progress mini-Hollands programme. Transportation Research Part A: Policy and Practice. 123, 2019, 147-169
Competing interests: Convener of the Medact Group: Prescription for Safe Cycling
Re: Every step you take - ‘And-and’ rather than ‘and-or’
In response to JC Kenington we agree that environmental and structural changes in landscapes, life spaces and public areas such as those cited by Kenington are efficacious in reducing sedentary time [1]. Interventions such as the ‘Green Prescription’ primary care activity counselling program which focuses on individuals showed a similar effect to the ‘Mini-Holland’ projects [2]. Public health interventions can and should be added to more individualised behavioural strategies. It is very likely that system based approaches are more effective in influencing sustainable activity behaviour compared to a single modality [3].
We promote ‘and-and’ rather than ‘and-or’ for multiple touch points both from individual approaches involving health care, and public health and environmental interventions to enable increased activity. In this context we further argue that walking is a promising target for interventions with low barriers. It is simple, affordable (free), achievable even for older adults, and rarely contraindicated.
References
1. Kenington JC, Re: Every step you take. Published Online First: 17 September 2019.https://www.bmj.com/content/366/bmj.l5051/rr (accessed 18 Sep 2019).
2. Elley CR, Kerse N, Arroll B, et al. Effectiveness of counselling patients on physical activity in general practice: cluster randomised controlled trial. BMJ 2003;326:793. doi:10.1136/bmj.326.7393.793
3. Rutten A; Frahsa A; Abel T; Bergmann M; de Leeuw E; Hunter D; Jansen M; King A; Potvin L. Co-producing active lifestyles as whole-system-approach: theory, intervention and knowledge-to-action implications. Health Promotion International. 34(1):47-59, 2019 Feb 01.
Competing interests: No competing interests