Does prolonged sitting really kill 70,000 people a y...

"Is sitting really the new smoking? Alarming new research claims 70,000 deaths a year are caused by our increasingly sedentary lives," reports the Mail Online.

This headline refers to a study that looked into the impact of sedentary behaviour on a range of conditions including type 2 diabetes and various cancers.

The main findings were that compared with being sedentary for less than 3 hours per day, being sedentary for more than 6 hours per day was associated with more than 69,000 deaths per year in the UK. However, the study was not able to prove that being sedentary directly caused this many deaths.

In total, the researchers estimated that the overall impact of sedentary behaviour cost the NHS around £700 million per year.

The study drew on data from various large studies, surveys and NHS cost data. However, the calculations were based on a number of assumptions and could not account for all possible risk factors for each condition.

Though it is likely that prolonged inactivity is bad for our health, we do not know from this study how much physical activity we need to offset the hours we spend sitting. A few extra minutes, or even an hour, spent standing is unlikely to have the same benefits as regular physical exercise.

Where did the story come from?

The study was carried out by researchers from Queen's University Belfast and Ulster University. One author was funded by a Department for the Economy (Northern Ireland) studentship.

The study was published in the peer-reviewed Journal of Epidemiology and Community Health.

In general the UK media have reported the story accurately, with most explaining that the conditions and deaths were linked to rather than directly caused by increased sedentary behaviour.

Many media sources included helpful commentary from independent experts, such as Dr Gavin Sandercock, from the University of Essex, who said that the effect of reducing sitting time "is pretty small in terms of health benefits … in contrast, getting people to be more physically active has much bigger effects".

What kind of research was this?

This was an economic impact study. It used data from previous cohort studies, UK health surveys and NHS budgets to estimate the impact of sedentary behaviour on a range of conditions.

As the calculations are based on a number of assumptions, this type of study can only provide an indication of how big the impact might be. It cannot prove that being sedentary caused each illness or cost to the NHS.

What did the research involve?

UK sedentary patterns were identified using Health Survey for England 2012 data. This showed that 30% of adults were sedentary for at least 6 hours per day during the week and this rose to 37% of adults at the weekend.

The researchers then searched for cohort studies that followed people over time to see who died from any cause or developed the following 5 conditions that have previously been linked to sedentary behaviour:

type 2 diabetes
cardiovascular disease
lung cancer
colon (bowel) cancer
endometrial (womb) cancer

These studies compared the lowest (0 to 3.8 hours per day) and highest (6 to 18 hours per day ) levels of sedentary behaviour and the risk of developing each condition. For type 2 diabetes this was measured in terms of the length of time spent watching television (approximately less than 1 hour compared to more than 5 hours).

Researchers combined the relative risks associated with sedentary behaviour in the UK and adjusted the results to take into account the level of sedentary behaviour reported at the start in each cohort study.

These risk figures were put into a formula to estimate the proportion of people who would not have developed the condition if they had been less sedentary, taking physical activity levels into account.

Then the researchers calculated the cost of these people developing each illness based on UK NHS healthcare budgets from Scotland, Wales and England, adjusting the figures to 2017. They took into account the fact that some people may have had more than one of these conditions.

What were the basic results?

The researchers estimated that 11.6% of deaths from any cause were associated with sedentary behaviour:

if people had not been sedentary, they calculated that 69,276 deaths could have been avoided in 2016

The proportion of the population whose illnesses were associated with sedentary behaviour were:

16.9% of people with type 2 diabetes (95% confidence interval (CI) 14 to 19.6)
5% of people with cardiovascular disease (95% CI 4.2 to 5.5)
7.5% of people with lung cancer (95% CI 3.9 to 11)
9% of people with colon cancer (95% CI 7.3 to 10.7)
8% of people with endometrial cancer (95% CI 6 to 10)

Overall, they calculated that sedentary behaviour cost the NHS £706 million in 2016/17. This figure takes into account that some people have more than one of the conditions.

How did the researchers interpret the results?

The researchers said the "total costs presented are likely to be a conservative estimate of the true burden of sedentary behaviour". They hope their "estimate can inform decision makers who are prioritising resources in healthcare and make a financial case for reducing sedentary behaviour in the UK".

Conclusion

This study has attempted to pool data to estimate the impact of sedentary behaviour on a range of conditions.

Strengths of the study include the use of data from large cohort studies plus NHS data.

However, the study also has some limitations, including:

sedentary behaviour levels were self-reported meaning they may not be entirely accurate. There are many risk factors for each condition that were not taken into account such as smoking, diet and excess alcohol intake
the categories of sedentary behaviour were quite broad – the higher level being between 6 and 18 hours. This would include a large section of the working population, for whom this level of sitting may be unavoidable, yet most of these people do not have the illnesses in question
physical activity levels were taken into account, but again these were self-reported

Due to these limitations the proportions of disease or deaths attributed to prolonged sitting – and associated health costs – should be considered as estimates.

Despite the limitations imposed by the underlying studies, this research supports health advice to reduce the amount of time spent sitting.

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