Around 50,000 Brits die a year because they spend too much time sitting around, according to a new study.
And it's costing the health system there more than $1 billion a year.
"Adults in the UK have become increasingly sedentary as modern technology has changed everyday life," researchers from the Queen's University Belfast Centre for Public Health write in the study, published in the British Medical Journal.
Defining sedentary behaviour as spending six hours a day "sitting or lying [awake] while expending low amounts of energy", they found almost a third of adults are sedentary during the week and slightly more on weekends.
Looking at how much the National Health Service spends on conditions related to sedentary behaviour, they found if less time was spent on the couch, the UK could save at least NZ$1.35 billion a year - probably more, since some conditions with only tenuous links to laziness - such as mental health disorders - were excluded from the analysis.
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And as many as 11.6 percent of all deaths could be avoided too - almost 50,000 a year.
"Strong evidence suggests that high levels of sitting time lead to increased risk of cardiovascular disease, type 2 diabetes and all-cause mortality," the study concluded.
"Additionally, moderate evidence indicates an increased risk of colon, endometrial and lung cancer. These diseases all contribute considerably to morbidity and mortality in the UK. Thus, addressing the problem of sedentary behaviour could potentially reduce the burden of disease."
A 2015 study by the New Zealand College of Public Health Medicine found similar results here, blaming a lack of physical exercise for 12.7 of all deaths.
The brains behind the latest study said employers should take note too, with physical inactivity having negative effects on productivity.
"Many individuals in the UK spend their leisure time in sedentary behaviour, and the workplace represents a significant proportion of unavoidable daily sitting time for many people."
It's the first scientific look at the cost of sedentary behaviour to the UK health system.
A NZ Ministry of Health survey from 2014 found only half of adult Kiwis exercise the recommended amount. A 2016 study published in The Lancet found New Zealand has similar levels of inactivity to the UK.