Emerging research paradigms in the battle against physical inactivity

27 November 2018 | Cancer research

Dr Paddy Dempsey is a National Health and Medical Research Council (NHMRC) Postdoctoral Fellow at the University of Cambridge. He discusses with us his research interests on the role of sedentary behaviour, physical activity and diet in the prevention and management of chronic diseases.

The message that regular physical activity is important for overall health and wellbeing, regardless of age, gender or body weight, is widely accepted. However, even if you are meeting current physical activity guidelines (something that few manage to achieve on a consistent basis), there remains another 16 or so waking hours in the day. Does it matter how you spend those waking hours, which account for over 90 per cent of the day? If you spent most of those 16 hours sitting, compared to standing or moving around, would it affect your health, and why?

Sedentary behaviour: a new focus within physical activity research

In recent years, the field of physical activity and health has witnessed the emergence of a distinctive paradigm focusing on sedentary behaviour. That is, any waking behaviour with an energy expenditure less than or equal to 1.5 metabolic equivalents (METs: a physiological measure expressing the energy cost of physical activities), while in a sitting, reclining, or lying posture. Device-based measures suggest that adults typically spend nine to ten hours per day sedentary across multiple settings (for example watching TV or driving a car), and accumulating evidence suggests that higher volumes of sedentary time are associated with an elevated risk of some cancers, as well as type 2 diabetes, cardiovascular disease and premature mortality. 

Although the narrative above has potentially powerful public health implications, the devil is in the detail. As the sedentary behaviour paradigm continues to mature, more evidence is needed concerning the strength, temporality and dose-response nature of associations, and to clarify whether sedentary behaviour (or sitting) per seis an ‘independent’ risk factor for adverse health outcomes. Other important lines of enquiry to pursue relate to a better understanding of underlying mechanisms and biological plausibility. Such evidence is important to:

  • Better understand the causal and interacting roles of sedentary behaviour and physical activity for human health.
  • Inform the specificity and potential targeting of interventions (such as the effective and pragmatic countermeasures), providing more precise information on what changes are required, why, and who will benefit.
  • Inform new physiological and molecular targets and therapies; such as drug discovery.  
  • Develop clear, evidence-based, clinical and public health guidance on sedentary behaviour as a health risk in order to better translate evidence into public health and policy actions. 

A workshop on sedentary behaviour 

To begin addressing these questions, the Sedentary Behaviour Council, chaired by Dr Brigid Lynch of Cancer Council Victoria and Dr Katrien Wijndaele from the University of Cambridge, hosted a full-day workshop featuring around 60 academic delegates; just prior to the 7th International Society for Physical Activity and Health (ISPAH) Conference. The theme for the workshop was Sedentary behaviour mechanisms – biological and behavioural pathways linking sitting to adverse health outcomes

The main aim of the workshop was to provide an up-to-date view on the state of the evidence on sedentary behaviour mechanisms, as well as set an agenda for moving the science forward. The morning session featured talks from distinguished and emerging researchers, who shared new findings from experimental and mechanistic studies on sedentary behaviour and chronic disease outcomes. In the afternoon, new methods to help extend our understanding of mechanisms and causal inference were highlighted, and subsequently discussed amongst the delegates in an interactive panel discussion. 

Guest speakers, back row: Charles Matthews, Nick Wareham, Tom Yates, David Dunstan, Audrey Bergouignan, Aiden Doherty. Front row: Brigid Lynch, Eline Van Roekel, Katrien Wijndaele.

The future of sedentary behaviour research 

There are significant challenges in determining the direct and indirect effects of longer-term sedentary behaviour patterns – with residual confounding and random measurement errors being key challenges in both physical activity and sedentary behaviour epidemiology research. Furthermore, behaviours that make up our 24-hour day (such as sedentary behaviour, physical activity, sleep and diet) fundamentally interact, and probably to different extents depending on relative dose, patterns, timings, and many other variables. And while our sedentary and physically-active behaviours appear to play an important role in human metabolic and vascular regulation, we still know very little about how various aspects of our physiology are affected – including cognitive, hormonal, immunologic, inflammatory and musculoskeletal systems – over the short and longer term. These aspects will require both detailed and integrated approaches.

The aetiological and mechanistic factors underlying activity behaviours and chronic disease are inevitably complex and challenging to study. However, a better mechanistic ‘diagnosis’ is crucial for improving causal inferences and developing evidence-based recommendations and public health policy actions. Triangulation of evidence from epidemiological, behavioural and interventional research on sedentary behaviour will most likely be required, as will improvements and refinements in measurement methods, research-designs and statistical analysis techniques. Developments in these areas should allow for more meaningful conclusions in the future. We need to acknowledge the inherent complexity, seek to better understand it, while also taking great care not to undermine our own clinical and public health messages around physical inactivity; the latter being an ‘art’ within itself!

  • Find out more about the mechanisms research that World Cancer Research Fund is supporting here.
Paddy Dempsey | 27 November 2018

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