Are you sitting comfortably?

When Dr Lee Smith is on the train to work, he does something a little odd: he stands up, while trying to ignore any strange looks from fellow passengers. He stays standing for about 15-20 minutes until he reaches Cambridge.

Standing, it seems, is the new sitting. And it can improve not only our physical health, but our mental health, too.

"There is a boom of interest in sedentary behaviours," explains Lee, who has made a bit of a name for himself in the field and is currently consulting for a large corporation to help improve the health of its workforce.

Sedentary behaviour is certainly one of the habits of our information age and spending too long sitting is associated with a number of problems: more body fat, type II diabetes, certain cancers (eg, prostate, breast and colo-rectal), and high levels of depression and low self-esteem.

As you might expect, this is a problem that is worse among those whose work is less manual – in high-income countries, among office workers, and among women more than men. But Lee's research suggests that older people and children are affected, too.

Lee's work focuses on promoting physical health and the role of exercise in surviving cancer. His work on sedentary behaviour hinges on three studies: one into sedentary behaviour and depression; one into TV watching and obesity; and a third called the 'Active Building' study which involved equipping 164 office workers with devices that measured their movements around their workspaces. He found that people who sit a lot in the week also sit a lot on weekends, almost to an identical degree. Habits can become dangerously ingrained.

"The thing most people are not aware of is that you can't entirely taking away the bad effects of sitting at a desk all day – or, indeed, of sitting on a sofa watching TV – by going to the gym. The damage is done and you can't completely erase it," says Lee, who takes his young son to play in the garden whenever he can, to help set good habits.

Research conducted by Lee's colleagues has shown that when we stand, we clear sugar from our blood more quickly than when we're sitting. After eating our blood sugar goes up and, if it stays high for too long, it can damage the lining of our blood vessels and increase the risk of heart disease and diabetes.

Lee's own study into television habits and obesity compared the viewing habits of more than 6,000 people. It concluded that children who watched a lot of television aged ten were 42% more likely to spend more than three hours in front of the screen as adults.

Meanwhile, Lee's study into sedentary behaviour and mental health looked at 42,000 men and women aged around 44 across many countries. It showed that people with depression spend 25 minutes more each day sitting than those without; with that margin increasing in the over-65s.

"Sitting a lot, even at work, encourages social isolation and limits our social networks, which is not good for us," says Lee. "What we are not sure about yet, is whether it is the depression driving the sedentary behaviour, or the sedentary behaviour driving the depression. It is probably both. Certainly, a lack of exercise can cause low mood because of the lack of endorphins, but this is only one factor. Not getting out means you socialise less which is also bad for mood."

So what can we do to counteract the effects of a sedentary lifestyle?

Standing desks are becoming increasingly popular, and Lee is carrying out a study into their uses and benefits. "Managers can worry that they will reduce their workers' productivity," explains Lee, "but we're comparing cognitive tasks undertaken while sitting and standing – and our preliminary findings suggest that there is no difference."

Lee also recommends some simple changes such as trying to break up every 20 minutes of sitting with two minutes of standing, playing active computer games instead of watching television, or going out for a walk or doing some gardening in the evening, rather than heading for the sofa.

And next time you're on a train, you could grab that standing spot by the door.

Sport and exercise research at ARU

Dr Lee Smith is Reader in Physical Activity and Public Health, and a member of our Cambridge Centre for Sport and Exercise Sciences. He's also leading our COVID-19 research group.