491

J Physiol 593.3 (2015) pp 491–492

PERSPECTIVES

Age is just a number! Or is it? 1

Philip J. Atherton and Paul L. Greenhaff2 1 MRC-ARUK Centre of Excellence for Musculoskeletal Ageing Research, Division of Medical Sciences and Graduate Entry Medicine, University of Nottingham, Royal Derby Hospital Centre, Derby, UK 2 MRC-ARUK Centre of Excellence for Musculoskeletal Ageing Research, School of Life Sciences, University of Nottingham, Queen’s Medical Centre, Nottingham, UK

The Journal of Physiology

Email: [email protected]

By 2035 it is estimated that people aged 65 years and over will account for 23% of the UK population. More startling perhaps is the prediction that by this time the number of people aged 85 years and over will account for 5% of the UK population, which is close to 2.5 times greater than it was in 2010 (Office for National Statistics, 2012). It is also notable that the 2012 EU Ageing Report (European Commission, 2011) revealed that strains on the healthcare services in the run up to death impact on expenditure more than ageing itself. Therefore, although increased life expectancy does not necessarily increase health expenditure, ill health in the final part of life certainly does. As such, it is imperative that research on the ageing process (i.e. independent of major confounding variables) is prioritised so that new strategies for improving health span and well-being in later life can be identified, thereby reducing pressure on the increasingly strained health/social care systems. It is irrefutable that many biological events associated with advancing age are due to complex and integrated alterations in multi-organ physiological systems, including reductions in skeletal muscle mass, quality and function (sarcopenia and dynapenia), declines in cardiovascular function, impaired cognitive ability, impaired sensorimotor performance, and brain structural and neurochemical deficits. Moreover, it is also the case that the relationship between chronological age and

physiological function is unpredictable; not least because of influences from heritable and lifestyle factors which impact on these physiological systems to different degrees. This raises the question to what extent are the biological features currently attributed to ‘ageing’ per se, in reality driven by lifestyle factors? Right at the top of the list of potentially influential lifestyle factors is physical inactivity. Indeed, physiological manifestations of ageing such as declines in muscle mass, locomotory function and insulin resistance are also common features of physical inactivity in young people. This suggests that declines in physical activity levels (that evidently accompany ageing) may be a central driver of age-related health issues, or, looked at another way, that inactivity may be a greater determinant of health span than chronological ageing per se. This may also, to some extent, explain the long-recognised epidemiological (but lesser so experimentally derived) associations between inactivity, development of non-communicable diseases and reduced quality of life in ageing. Such facets relating to understanding ‘natural or intrinsic’ biological ageing processes in the context of contributory lifestyle factors such as physical in/activity nonetheless represent a major knowledge gap. Indeed, while in 400 BC Plato postulated that “lack of activity destroys the good condition of every human being, while movement and methodical physical exercise save and preserve it”, precisely how this links to biological ageing is poorly defined. A paper by Pollock et al. (2015) in this edition of The Journal of Physiology provides a valued contribution to this area of physical in/activity and ageing. The authors assessed relationships between chronological age and a range of traditional physiological parameters in 125 (84 males, 41 females) amateur, non-elite cyclists aged 55–79 years (see their Tables 1 and 2), whom it was proposed by the authors represented a model for the study of human ageing free from a number of lifestyle influences, in particular, physical inactivity. The authors’ main rationale was that ‘removing’ the confounding influence of

 C 2015 The Authors. The Journal of Physiology  C 2015 The Physiological Society

physical inactivity might promote clearer (individualised) association(s) between physical and metabolic parameters and chronological age. Specific inclusion criteria ensured that all volunteers were deemed to be healthy (i.e. not suffering from chronic diseases, not on medications, no tobacco use) and engagement in chronic, high level physical activity (all males could cycle 100 km in under 6.5 h, and females 60 km in under 5.5 h; subjects were required to demonstrate this twice in the 3 weeks prior to study inclusion). Each participant underwent detailed physiological profiling, including, for example, measures of genetic (targeted SNPs), cardiovascular, respiratory, neuro-muscular, metabolic, endocrine and cognitive functions, body composition and mental well-being. The authors were able to demonstrate a number of statistically significant associations between chronological age and physiological function, with rates of maximal oxygen consumption showing the strongest association with chronological age (r = −0.443 to −0.664; P < 0.001). Given that links between aerobic capacity and health/disease risk have been established, this association in particular is perhaps not too surprising. Nonetheless, despite undertaking a battery of physiological tests, no individualised associations were sufficiently robust to be able to reliably track with chronological age. It would appear therefore based on the data of Pollock et al. (2015) (and to some extent logic) that the relationship between chronological age and conventional physiological function is complex and heterogeneous. Moreover, the likelihood that removing inactivity would improve the predictive capacity between chronological age and gross measures of physiological function is perhaps debatable, particularly considering the study design did not control for sedentary behaviours or years of cycling. On this basis, future research should determine whether stronger associations exist between chronological age and more precise and sensitive measures of human metabolic and physiological function with defined levels of activity and inactivity. Notwithstanding this, the authors have undertaken an

DOI: 10.1113/jphysiol.2014.288373

492 important study, and the associations elucidated by Pollock et al. point to physical inactivity being a potential confounding factor in ageing research. Indeed, if true relationships between age and physiological function are to be elucidated, studies that control for habitual physical activity levels (and other likely confounding variables) are urgently needed. Moreover, these studies should be performed in humans, the best model of human ageing (Demetrius, 2005) if robust insight and biomarkers are to be established; indeed, we are in a technologically advanced and omics-driven

Perspectives era where insightful data can be derived from in vivo studies, directly in humans.

References Office for National Statistics (2012). Population ageing in the United Kingdom, its constituent countries and the European Union. Office for National Statistics, London. European Commission (2011). The 2012 ageing report: underlying assumptions and projection methodologies. European Economy 4, 1–310.

J Physiol 593.3

Pollock RD, Carter S, Velloso CP, Duggal NA, Lord JM, Lazarus NR & Harridge SDR (2015). An investigation into the relationship between age and physiological function in highly active older adults. J Physiol 593, 657–680. Demetrius L (2005). Of mice and men. When it comes to studying ageing and the means to slow it down, mice are not just small humans. EMBO Reports 6, S39–S44.

Additional information Competing interests

None declared.

 C 2015 The Authors. The Journal of Physiology  C 2015 The Physiological Society

Copyright of Journal of Physiology is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.

Age is just a number! Or is it?

Age is just a number! Or is it? - PDF Download Free
61KB Sizes 2 Downloads 8 Views