Sedentary behaviour

The book review section of my Sunday paper has, as its book of the week, “The Brain at Rest” . The subtitle is “Why doing nothing can change your life”! The book’s message is clear – the benefits of a life of physical idleness are great for the brain and for psychological well-being. To gain these benefits we need long baths, daily naps, lying on the bed daydreaming , computer games etc. A very seductive idea.

The book fails to warn us about all the side effects of physical inactivity which has acquired the medical sounding title of “sedentary behaviour”.

Sedentary behaviour (SB)

Doing nothing, indulging in this sedentary way of life, is the antithesis of exercise and physical activity which sadly has its own health risks. The more you sit about (indulge in SB) the greater the risk to your health.

Sedentary behaviour is any time spent primarily sitting or lying down and which involves expenditure of 1.5 metabolic equivalents (METs) or less. Examples are sitting, watching television, playing video games, and using a computer. Too much sitting, however, is distinct from too little exercise. Just sitting about is dangerous in its own right even if you do take enough exercise. For adults who meet the minimal public health recommendations on physical activity on most days each week, the 9–10 hours of sitting that can occupy their remaining, ‘non-exercise’, time can still have a damaging effect on their health. A new physical-activity grouping known as ‘active couch potatoes’ has emerged: those who apparently take the recommended amount of exercise but spend excess time just sitting around.

The harmful effects of too much sitting

The risk of death increases for any sedentary time greater than 7 hours a day.  Both total sedentary time per day and length of sedentary bouts are predictors of premature death and the combination of the two triples the risk of premature mortality.  This has even received a label – ‘the sedentary death syndrome’.

The news is not all bad. Though regular exercise does not eliminate the perils induced by too much time in front of a screen, it does reduce the impact. A meta-analysis involving more than 1 million souls found that they needed to watch television for more than 5 hours per day to reduce the benefits of a regular exercise habit. About an hour’s exercise a day offsets the ill effects of sitting at work for 8 hours.

The more you sit about, the higher your risk of developing cardiovascular disease and diabetes – independent of the amount of exercise you take when not sitting about. The extent of the damage from sedentary behaviour has been quantified by a study conducted in Dallas, Texas, of the coronary calcium scores in heart patients. This score indicates the amount of calcium detectable in coronary arteries and is a good indicator of the presence of coronary narrowing, with its attendant risks of heart attacks and sudden death. For this group of over 2,000 patients, each hour of sedentary time per day on average was associated with a 14 per cent increase in coronary-artery calcification. TV viewing time has also been under the microscope. For every additional hour per day of watching the gogglebox there is an increase in the risk of cardiovascular disease of 3 per cent and an increase in BMI of 0.54. Other conditions that have been shown to be aggravated or even caused by too much sitting about include obesity and some cancers, while the death rate from all causes is increased.

Are we becoming less sedentary?

A couple of recently published articles led me back to this subject.

1. Is SB decreasing?A recent survey of activity among a representative sample in the USA found that average sedentary time decreased from 7.1 hours per day in 3013-14 to 5.9 hours per day in 2017-20 and has remained stable since. That sounds like excellent, if rather unlikely, news but may not be as good as it sounds. One commentator noted that the SB was estimated from self-reported activity by answering a questionnaire. The questionnaire included how long the subjects spent each day playing cards but not how long spent in bed scrolling through social media sites!I would add that data about such habits which rely on questionnaire responses are likely to be highly inaccurate.If you want to know the truth about how much people eat, how much they drink or how much they exercise you must measure it – it is no good asking the subjects being studied. It has been reckoned that people:
   *  eat about 50% more than they declare
   *  drink about 50% more alcohol than they say and
   * exercise about 50% less than they claim.
2. Can exercise reverse the damage incurred by SB?This study published in The Journal of the American College of Cardiology reported on nearly 90,000 men and women average age 62 whose activity levels and sedentary time were actually measured using an accelerometer (a sophisticated pedometer). Average sedentary time was 9.5 hours per day (that’s a bit convincing). They found that SB is associated with increased risk of heart failure and risk of death from cardiac disease. The”inflection” point – the point at which risk increased sharply – was 10.6 hours per day of SB. They found some, but only partial, protection from adhering to the DoH recommendation of  150 minutes or more of moderate to vigorous activity per week.None of this is very new information but it does remind us that sitting about is bad for our physical health even if it does improve mental health, as promoted by “The Brain at Rest”.