Researchers at Queen's have found that spending large amounts of time sitting or lounging around during the day is linked to around 70,000 deaths per year in the UK.
This amounts to more than £0.7bn per year in costs to the NHS for treating the health consequences.
A large proportion of the UK population have sedentary jobs and leisure activities, and official physical activity recommendations regarding sedentary behavior are vague.
Lead Investigator, Leonie Heron from the Centre of Public Health at Queen's University Belfast, said: "We know that spending large parts of the day sitting down increases the risk of a number of illnesses including cardiovascular disease and diabetes. This research has enabled us to put a figure on this, demonstrating the huge cost this has on the NHS and highlights the pressing need to address this issue to both reduce the financial cost and improve population health.
"Our research showed that sedentary behavior contributed to almost 70,000 lives lost in 2016. This could have been avoided if sedentary behavior was eliminated in the UK."
Researchers at Queen's University Belfast and Ulster University extrapolated data from previous studies to assess the financial impact of sedentary behavior on the NHS for the first time, published today (Tuesday 26 March) in the Journal of Epidemiology & Community Health.
Figures calculated by other researchers on the impact sedentary behavior has on the relative risks of five specific health conditions (type 2 diabetes, cardiovascular disease, colon cancer, endometrial cancer and lung cancer) and deaths from all causes were combined with figures on the percentage of adults who are sedentary on any given day of the week to estimate the overall impact sedentary behavior has at a UK population level (population attributable fraction).
Figures on sedentary behavior were taken from the Health Survey for England 2012, which reported that 30 per cent of adults in England spent at least six hours/day sedentary on weekdays and that this increased to 37 per cent of adults on weekends.
Actual overall NHS spending on each of the five conditions, uplifted for inflation, was used to estimate the financial impact sedentary behavior had on the NHS for each of the conditions in the UK in 2016-17.
For all five conditions combined, this amounted to £0.8bn in 2016-17.
As a proportion of patients will have more than one of the five conditions, for example around 30 per cent of people with type 2 diabetes will also have cardiovascular disease, the researchers revised their figures to adjust for double-counting caused by comorbidity. This reduced the overall cost of sedentary behavior to the NHS for these five health conditions to £0.7bn in 2016-17.
Next they took the figure calculated for the fraction of deaths from all causes that could be attributed to a sedentary lifestyle and multiplied it with the actual numbers of deaths that occurred in the UK in 2016.
The researchers say their results suggest that 11.6 per cent of all deaths were associated with sedentary behavior and that 69,276 deaths might have been avoided in 2016 if sedentary behavior was eliminated in the UK.
Ms Heron added: "This is a conservative estimate of the true burden of sedentary behavior because sedentary behavior is likely to be associated with other cancers, musculoskeletal disorders, and mental health disorders, not included in their analysis.
"Many individuals in the UK spend their leisure time in sedentary behavior, and the workplace represents a significant proportion of unavoidable daily sitting time for many people. Measures should be taken to reduce sedentary behavior with the aim of improving population health and reducing the financial burden to the health service."