Sitting for too long can shorten your lifespan and shrink your brain. Why is prolonged inactivity so bad for us?

Toronto Star

23-05-2025

Modern life demands a lot of sitting.
Maybe you sit for an hour-long drive to the office, where you saunter from sitting in cubicles to sitting in meetings. Perhaps you're a bus or truck driver, spending long hours strapped to your seat. If you're anything like me, you unwind from a long day of sitting by sitting in front of a screen for a few more hours.
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All that sitting builds up. And years of sedentary living can shave years off your lifespan — or even kill you.
'Humans were hunter-gatherers and moving all the time,' said Catherine Sabiston, a University of Toronto professor and the Canada Research Chair in physical activity and mental health. 'So now that we've become more sedentary, there are all these extra detriments to our physical and mental health.'
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In rare cases, sitting for too long can kill you
In May of 2011, 20-year-old Chris Staniford was on his way to a job interview when he suddenly collapsed dead outside the Sheffield, England job centre.
Staniford's family told reporters their child was an avid gamer, often spending up to 12 hours straight on Xbox Live. The night before he died, Staniford was reportedly up late gaming when he felt a pounding in his chest. He ignored it and went to sleep.
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During the autopsy, a coroner found a blood clot wedged deep inside Staniford's lungs. This clot, known as a deep vein thrombosis, had originally crystalized in his left calf; it was nurtured in the pooled blood of his resting leg, where the blood vessels were obstructed by hours of uninterrupted sitting.
One day, the clot broke free, migrated into Staniford's lungs and caused his death — a pulmonary embolism.
It's a rare but not unprecedented outcome of prolonged sitting, explained Jason Au, an assistant professor of kinesiology at the University of Waterloo whose lab is researching the subject.
'This is not a concern for most of the population who sit during the day,' he said, noting that people who sit for more than eight hours at a time without moving are only at mild risk. 'It is extremely unlikely that this will occur in an office setting.'
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Pulmonary embolism is a rare and extreme outcome of a sedentary lifestyle. Sitting for too long can cut our lives short in other ways.
What years of sitting does to your body
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Every time we move, our activated muscles are also stroking and squeezing nearby blood vessels, helping to push blood, as well as the oxygen and nutrients it carries, to the muscles and organs where it's needed.
When we sit — even if only for an hour — the resting muscles and obstructed blood vessels in our legs can allow blood to pool, Au said. Over time, it can reduce blood flow, shrink the size of our arteries and contribute to swelling in the legs.
Too much sitting has been linked to obesity, high blood pressure, worse blood-lipid profiles, metabolic issues like type two diabetes, and musculoskeletal issues like back pain and muscle fatigue. It's also associated with heart disease and cancer.
Researchers found people who spent more than eight hours a day sitting with no physical activity had about the same risk of dying as those who smoke or are obese. And the longer you spend inactive, the higher your risk of all-cause mortality, suggested a similar 2014 paper that surveyed older women.
'Whether someone gets metabolic disease or cardiovascular disease, the end result unfortunately is death,' Au said. 'These things don't happen overnight. This is an accumulation of lifestyle effects.'
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What a sedentary life does to your brain
Too much sitting can also waste away our brains and heighten our risk of dementia, said Dr. Donald Weaver, a neurologist and senior scientist at the University Health Network's Krembil Brain Institute.
'Everything you do feeds into your brain,' he said. 'As you walk, every step that you take, all of that is information that's stimulating your brain ... Sitting and doing nothing doesn't give you the physical stimulation that we now recognize as an essential component of brain health.'
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A recent study of older adults found the more someone sat, the more certain regions of their brain shrank and degraded — upping their risk of neurodegenerative diseases like Alzheimer's. This happened despite the large majority of participants meeting recommended weekly exercise guidelines.
That doesn't happen because you spent one night gaming. It's the result of decades of sedentary behaviour, Weaver explained: 'The foundation for you setting yourself up for dementia or depression starts early in life ... Lifestyle changes that are made in your 20s or 30s are going to have a long-standing impact on your brain health for the rest of your life.'
Sitting for too long can also raise our risk of depression and anxiety, hamper our emotional regulation and reduce our motivation, Sabiston said. The result is worse overall mental health.
'Generally speaking, if you live more sedentary, then it disrupts other lifestyle behaviours like sleep and physical activity as well,' she added.
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Can I undo the damage?
The average Canadian adult spends 9.8 hours of their waking lives sedentary, including 5.7 hours spent sitting and 3.2 hours staring at a screen recreationally, according to Statistics Canada.
That's too much inactivity — Canadian guidelines recommend no more than eight hours of sedentary behaviour. And the research is split on how much of this damage is reversible. Some studies suggest regular exercise can counteract poor health outcomes no matter how much we sit, while others note health affects regardless of exercise.
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The best way to counter inactivity is to break up our sitting time, the experts say. For example, after sitting for an hour, take two to three minutes to walk and stretch your legs, Sabiston said.
Outside of work, try to get at least 150 minutes of moderate aerobic activity each week and at least two sessions of muscle strengthening exercises, according to the Canadian 24 hour Movement Guidelines.
The sooner we incorporate regular physical activity into our lives and limit our time sitting, the better our future health outcomes, according to the experts. But even if we can't fully alleviate the health outcomes following decades of sedentary behaviour, getting more exercise can still benefit our health.
'It's never too late to get up and get active,' Weaver said. 'But the sooner you do it in your life, the better.'