When a new group of interns recently arrived at Barclays in New York, they discovered a memo in their inboxes. It was from their supervisor at the bank, and headed: “Welcome to the jungle.” The message continued: “I recommend bringing a pillow to the office. It makes sleeping under your desk a lot more comfortable … The internship really is a nine-week commitment at the desk … An intern asked our staffer for a weekend off for a family reunion – he was told he could go. He was also asked to hand in his BlackBerry and pack up his desk.”

Although the (unauthorised) memo was meant as a joke, no one laughed when it was leaked to the media. Memories were still fresh of Moritz Erhardt, the 21-year-old London intern who died after working 72 hours in a row at Bank of America. It looked as if Barclays was also taking the “work ethic” to morbid extremes.

Following 30 years of neoliberal deregulation, the nine-to-five feels like a relic of a bygone era. Jobs are endlessly stressed and increasingly precarious. Overwork has become the norm in many companies – something expected and even admired. Everything we do outside the office – no matter how rewarding – is quietly denigrated. Relaxation, hobbies, raising children or reading a book are dismissed as laziness. That’s how powerful the mythology of work is.

Technology was supposed to liberate us from much of the daily slog, but has often made things worse: in 2002, fewer than 10% of employees checked their work email outside of office hours. Today, with the help of tablets and smartphones, it is 50%, often before we get out of bed.

Some observers have suggested that workers today are never “turned off”. Like our mobile phones, we only go on standby at the end of the day, as we crawl into bed exhausted. This unrelenting joylessness is especially evident where holidays are concerned. In the US, one of the richest economies in the world, employees are lucky to get two weeks off a year.

You might almost think this frenetic activity was directly linked to our biological preservation and that we would all starve without it. As if writing stupid emails all day in a cramped office was akin to hunting-and-gathering of a previous age … Thankfully, a sea change is taking place. The costs of overwork can no longer be ignored. Long-term stress, anxiety and prolonged inactivity have been exposed as potential killers.

Researchers at Columbia University Medical Center recently used activity trackers to monitor 8,000 workers over the age of 45. The findings were striking. The average period of inactivity during each waking day was 12.3 hours. Employees who were sedentary for more than 13 hours a day were twice as likely to die prematurely as those who were inactive for 11.5 hours. The authors concluded that sitting in an office for long periods has a similar effect to smoking and ought to come with a health warning.

When researchers at University College London looked at 85,000 workers, mainly middle-aged men and women, they found a correlation between overwork and cardiovascular problems, especially an irregular heart beat or atrial fibrillation, which increases the chances of a stroke five-fold.

Labour unions are increasingly raising concerns about excessive work, too, especially its impact on relationships and physical and mental health. Take the case of the IG Metall union in Germany. Last week, 15,000 workers (who manufacture car parts for firms such as Porsche) called a strike, demanding a 28-hour work week with unchanged pay and conditions. It’s not about indolence, they say, but self-protection: they don’t want to die before their time. Science is on their side: research from the Australian National University recently found that working anything over 39 hours a week is a risk to wellbeing.

Is there a healthy and acceptable level of work? According to US researcher Alex Soojung-Kim Pang, most modern employees are productive for about four hours a day: the rest is padding and huge amounts of worry. Pang argues that the workday could easily be scaled back without undermining standards of living or prosperity.

Other studies back up this observation. The Swedish government, for example, funded an experiment where retirement home nurses worked six-hour days and still received an eight-hour salary. The result? Less sick leave, less stress, and a jump in productivity.

All this is encouraging as far as it goes. But almost all of these studies focus on the problem from a numerical point of view – the amount of time spent working each day, year-in and year-out. We need to go further and begin to look at the conditions of paid employment. If a job is wretched and overly stressful, even a few hours of it can be an existential nightmare. Someone who relishes working on their car at the weekend, for example, might find the same thing intolerable in a large factory, even for a short period. All the freedom, creativity and craft are sucked out of the activity. It becomes an externally imposed chore rather than a moment of release.

Why is this important?

Because there is a danger that merely reducing working hours will not change much, when it comes to health, if jobs are intrinsically disenfranchising. In order to make jobs more conducive to our mental and physiological welfare, much less work is definitely essential. So too are jobs of a better kind, where hierarchies are less authoritarian and tasks are more varied and meaningful.

Capitalism doesn’t have a great track record for creating jobs such as these, unfortunately. More than a third of British workers think their jobs are meaningless, according to a survey by YouGov. And if morale is that low, it doesn’t matter how many gym vouchers, mindfulness programmes and baskets of organic fruit employers throw at them. Even the most committed employee will feel that something is fundamentally missing. A life.

Peter Fleming’s new book, The Death of Homo Economicus: Work, Debt and the Myth of Endless Accumulation, is published by Pluto Press (£14.99rrp). To order a copy for £12.74 with free UK p&p, go to guardianbookshop.com