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15.10.2016 - Ausgabe: 5/2016

"Sitting endangers your health" On the health risks of the sedentary lifestyle

By Prof. Dr. phil. Gerhard Huber, Institute of Sport and Sport Science, University of Heidelberg

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"Is sitting a lethal activity?" was the title of an article that appeared in the New York Times on 14 April 2011. Its subject was the result of a re-analysis of data collected during a cancer prevention study; the purpose was to determine the correlation between relative time spent seated or in physical activity and the risk of mortality (Patel et al. 2010). In fact, in the case of those subjects who were sedentary for more than six hours per day (in comparison with those who were seated for shorter periods), it was established that:

 

there was a 40% higher risk of mortality in the case of women

there was a 20% higher risk of mortality in the case of men

there was a 94% higher risk of mortality in the case of women who were least   active overall

there was a 40 % higher risk of mortality in the case of men who were least       active overall

 

It has long been clear that physical activity plays a major role in maintaining health and well-being. There is also sufficient evidence that those who undertake at least moderate physical exercise for just 150 minutes (per day) are doing enough to reduce their risk of developing most of the forms of chronic disorders (Niebauer et al. 1997, Wen et al. 2011). Sadly, available epidemiological statistics show that all too few individuals manage to meet even this minimal requirement (Kruger et al. 2007). And there is growing proof that the antithesis of physical activity, namely sitting, is associated with considerable dangers to health and needs to be considered in the context of prevention strategies.

 

The sedentary lifestyle

Recent studies and overviews have demonstrated that is there a significant link between a sedentary lifestyle and the emergence of many health problems, such as obesity. There is still no consensus as to whether sitting itself represents a separate risk factor or is simply the most common form of physical non-activity. Both hypotheses can be corroborated but it is my intention here not to go into detail on this. The fact remains, however, that if an individual reduces the time they spend sitting, this results in most cases in an increase in their level of physical activity.

The prevalent lifestyle that has developed particularly in the industrialised countries of the west has brought with it dramatic changes to the periods we spend sitting down. We sit

while travelling to and from work

at work

while eating

at home in front of the TV

Sitting is an activity that is characterised by a particularly low level of energy consumption. It is only slightly greater than that when lying down and only 50% of that when standing.

 

Sitting as a universal activity

In addition to looking at the forms of physical activity in terms of levels of energy consumption, it is also possible to differentiate between them on the basis of the acronym 'FITT', whereby

F = frequency

I = intensity

T = time

T = type of activity.

 

Tremblay et al. (2010) have suggested that an analogous (and appropriately named) system - 'SITT' - should be used to classify forms of sedentary activity:

 

S = sedentary behaviour frequency

I = interruptions

T = time

T = type of sitting (e.g. in a car or an office etc.)

 

Increasingly conclusive studies concerning the epidemiology of sitting are being published (Dunstan et al. 2012). It can also be assumed that there was no period in the past in which human beings spent so much time seated as they do today. In a study undertaken by Healy et al. 2007 (cf. Owen et al. 2008), accelerometers were used to register the number of hours spent in sedentary activities over the course of a day. The results are shown in Fig. 1. Undoubtedly there is a high level of intraindividual variation but at the same time it is clear that many individuals are sedentary for the critical period of more than one third of their waking hours.

 

In their study population of more than 240,000 US citizens, Matthews et al. (2012) demonstrated that the length of time the subjects were sedentary - particularly when seated in front of the TV - correlated with an increase in mortality of up to 60%. A major Australian cohort study in which more than 600,000 subjects were monitored reports a linear correlation between increased risk of mortality and time spent seated (“All-cause mortality hazard ratios were 1.02 (95% CI, 0.95-1.09), 1.15 (1.06-1.25), and 1.40 (1.27-1.55) for 4 to less than 8, 8 to less than 11, and 11 or more h/d of sitting, respectively, compared with less than 4 h/d, adjusting for physical activity and other confounders” [van der Ploeg et al. 2012, p. 494]). Since then, various articles, reviews and appeals have appeared with titles such as "Don't Just Sit There: Stand Up and Move More, More Often” (Dunstan & Owen 2012).

The ways that sitting can impinge on our health are very similar to those of a generally sedentary lifestyle. Weller & Corey (1998) observed that the rate of cardiovascular mortality increased by a factor of 2.7 in association with longer periods spent seated.

An analysis of the data collated during the Women’s Health Initiative Observational Study (n= 71,018) shows that individuals who are seated for more than 10 hours per day and otherwise indulge in little physical activity have a significantly increased risk of developing cardiovascular disorders (Chomistek et al. 2013). Green et al. (2013) came to a similar conclusion and were also able to demonstrate a correlation between time seated and hip circumference. These results are further confirmed in a Chinese study in which nearly half a million subjects participated (Du et al. 2013).

In general, the consequences for health of a lifestyle that involves excessive sitting can be compared with those of physical inactivity. Along a timeline, it is possible to differentiate between the following types of effect:

Direct effects
Next to sleep, sitting is that activity associated with the lowest level of energy consumption (see above). The initial direct effect of excessive sitting involves the energy balance; because nutritional intake remains relatively unchanged, this inevitably results in an excess of energy in the body and this excess energy is deposited in the form of fat. Another direct effect is 'disuse syndrome', in other words, bodily organs are no longer employed in their appropriate physiological form and extent. Structures that are not used will atrophy.

Physiological effects
Currently available data indicate that one of the most important health-promoting outcomes associated with physical exercise is the inflammatory inhibition that results from muscular activity (cf. Pedersen et al. 2007, Brandt & Pedersen 2010). Moreover, sitting can result in the dysfunction of metabolic processes, such as that responsible for glucose transport to muscle cells (Kennedy et al. 1999) and in massive problems with vascular functions. In addition, excessive sitting generates the muscular dysbalances that are associated with numerous conditions - there is, for example, the high incidence of back pain. Bone metabolism is particularly sensitive to this form of inactivity as this is dependent on the continuous trophic stimulation provided by upright activity.

Pathological effects
With this in view, it is apparent that many of the conditions that are caused by inactivity can be promoted by sitting. These include cardiovascular disorders, type 2 diabetes (cf. here Healy et al. 2008) and cancer (“Our findings further suggest that light-intensity activity may have a protective effect, and that sedentary time may independently contribute to breast cancer risk” Lynch et al. 2011, 183). With regard to bone metabolism, the risk of osteoporosis can be increased, particularly in women after the menopause.

Premature death
Large scale epidemiological studies have now shown that physical activity can have a life-prolonging effect and can thus even have a positive influence on that most ultimate of all factors, mortality. Remarkable is the fact that this applies to all causes of death, even to those on which physical activity has no influence, such as accidents, poisoning, suicide and violence. The already cited study by Patel et al. (2010) impressively demonstrates the long term effects of too much time spent seated and that the risk of premature mortality increases significantly with sedentary behaviour frequency.

 

 

Please contact P@L for a list of references.

 

Photo: @highwaystarz - fotolia.com

 

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