Re: Healthier ageing
As 2012 is the European Year of Active Ageing and Solidarity between Generations, it is fantastic to see articles which promote change in lifestyle for healthy ageing. However the article by Myint and Welch  fails to do justice to the first UK wide recommendations for physical activity . In particular they neglect to mention the most novel aspect of these recommendations, which is, at all ages, to reduce time spent being completely sedentary. Sedentary behaviour is not a lack of physical activity but is an umbrella term for behaviours where sitting or lying is the dominant mode of posture and energy expenditure is very low. The “Start Active Stay Active” recommendations  clearly state that long periods of sedentary behaviour are an independent risk factor for health and wellbeing. In other words, long periods of sitting between periods of activity have deleterious effects on health and wellbeing even if an individual meets the recommended guidelines for moderate intensity physical activity . We have known for some time that bed rest is not good for health, the Dallas bed rest study has shown that three weeks bed rest is equivalent to 30 years of ageing, but it seems that even shorter sedentary periods have considerable effect 
These recommendations from the four nations Chief Medical Officer’s  makes explicit that long periods of sitting should be minimised at all ages, including older adults. Currently this message cannot be more precise because the actual dose response is not known . Most of the research has focused on sedentary behaviour in children, despite the fact that older adults are the most sedentary segment of society . We agree with Myint and Welch that future research should seek to establish link between lifestyle and the ageing process. Research on the relationship between sedentary behaviour and ageing should be part of this agenda . The difficulty in establishing the effects of sitting on health and wellbeing partly lie with the broad definition of sedentary behaviour. It is difficult to fathom that all periods of sitting are deleterious to health, especially later in life when many feel it’s their time to do less. So concurrent efforts to develop a classification system  of sedentary behaviours and better sensing and analysis methodologies  need to be an integral part of refining guidelines for practice.
1 Myint P, Welch A. Healthier ageing. BMJ 2012;344:e1214.
2 Department of Health, Social Services and Public Safety, Scottish Government, Welsh Government, Department of Health. Start active, stay active: a report on physical activity from the four home countries' Chief Medical Officers. 2011.
3 Owen N, Healy GN, Matthews CE, Dunstan DW. Too much sitting: the population health science of sedentary behavior. Exerc Sport Sci Rev 2010;38:105-113.
4 McGuire D, Levine B, Williamson J, Snell P, Blomqvist C, Saltin B, Mitchell J. A 30-Year Follow-Up of the Dallas Bed Rest and Training Study. Circulation 2001;104:1350:1357.
5 Department of Health. Sedentary Behaviour and Obesity: Review of the Current Scientific Evidence. 2010.
6 NHS Information Centre. Health survey of England 2008. Physical activity and fitness. Summary of key findings 2009.
7 Owen N, Sugiyama T, Eakin EE, Gardiner PA, Tremblay MS, Sallis JF. Adults' sedentary behavior determinants and interventions. Am J Prev Med 2011;41:189-196.
8 SIT: Sedentary behaviour Internaitonal Taxonomy [www.sedentarybehaviourclassification.net]
9 Chastin SFM, Granat MH. Methods for objective measure, quantification and analysis of sedentary behaviour and inactivity. Gait Posture 2010;31:82-86.
Competing interests: No competing interests