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In these  “stay at home” days many of us will have found ways to keep active and many may have actually increased their exercising. However most of us will have found ourselves doing much more sitting about.

Why is this important? Beware! Exercise or no exercise, sedentary time is harmful for us.

Sedentary behaviour

I wrote about this some months ago and am resuscitating the topic because of its topicality to our current situation. So forgive some repetition. Sedentary behaviour is any time spent primarily sitting or lying down and which involves expenditure of 1.5 metabolic equivalents (METs) or less ie very little indeed.  The commonest example nowadays is screen time, be it TV, laptop, most video games, mobile phone or surfing the net.

Excess sedentary behaviour can be found in people who take a lot of vigorous exercise. Even among adults who meet recommended physical activity levels and who sleep for eight hours per night, it is possible to spend the vast majority of the day (up to 15 hours) sitting down.The 2008 Health Survey for England (HSE) survey reported that around 40% of adults spend 6 hours or more per day sitting down at weekends and slightly fewer on weekdays. Since then the situation has deteriorated. A more recent assessment of sedentary behaviour comes from the HSE 2012. The self-reported average daily sitting time was 5.4 hours for men and 5.1 hours for women at weekends and 4.9 hours for men and 4.7 for women on weekdays. In each case about 3 hours per day was spent watching TV. The trend was for more sedentary behaviour among the young (16 to 24) with an average sedentary time of 7 hours/day, and the old (70 to 79) at 9 hours /day, the so-called U shaped curve. The figures from the US are similar. A national study of nearly 6,000 adults in 2015/6 found that 26% sat for more than eight hours per day.

The danger

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, there are still deleterious metabolic consequences of the 9 to 10 hours of sitting that can occupy their remaining “non-exercise” time.  A new physical activity population known as ‘active couch potatoes’ has emerged – those who apparently take the recommended amount of exercise but spend excess time just sitting around. The current virus emergency must surely be increasing the numbers.

The risk of premature death increases for any sedentary time greater than 7 hours/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 more you sit about the higher the risk of developing both heart disease and diabetes – independently 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 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. Each hour of sedentary time per day on average was associated with a 14% increase in coronary artery calcification.

Other conditions which have been shown to be aggravated or even caused by too much sitting about include obesity, some cancers and all cause mortality.

Sedentary behaviour brings a substantial cost to the national purse. A Belfast study of sedentary behaviour for the year 2016-2017 estimated that the cost to the NHS was £700m per annum with most of this due to the increased prevalence of heart disease, diabetes and several forms of cancer.

Does regular exercise help?

The news is not all bad. Though regular exercise does not eliminate the perils induced by too much sitting about, it does reduce the impact. A meta-analysis involving more than 1 million souls found that you needed to watch television for more than five hours /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 eight hours.

What to do

How best to reduce sedentary behaviour then? There is no shortage of ideas given by the authors of the Dallas Heart Study paper – take a walk at lunchtime, pace about when on the phone, take the stairs not the lift, use a pedometer as a prompt to keep moving. Fidgeting also helps and has been shown to reduce the mortality risk from too much sitting about – even if it does infuriate your spouse.

PS

I remain very concerned by the government’s approach to our recovery from the mess we find ourselves in. There has been much talk about the “exit strategy” but little in the way of detail. If the authorities are as efficient in this field as they have been in the provision of virus testing and in the supply of personal protective equipment we have a lot to worry about.

Here are my recommendations:
1. Start widespread Covid-19 antibody testing ASAP – aiming to test as many of the population as possible.
2. Investigate and confirm the true resistance to reinfection of those who have antibodies.
3. Release the antibody positive people back into normal commercial life – opening shops, restaurants, pubs etc – and allow the immune to go back to being consumers.