The sixteen-year investigation, which drew on data from 194 countries, concluded that working 55 hours or more a week is associated with a 35 per cent higher risk of stroke and a 17 per cent higher risk of dying from ischemic heart disease, compared with a 35 to 40 hour working week.
Long working days are killing hundreds of thousands of people each year, the World Health Organisation say.
The first global study of the phenomenon, carried out by the WHO and the International Labour Organisation, has been published in the Environment International journal.
Maria Neira, director of the WHO’s Department of Environment, Climate Change and Health, said that working long hours is a “serious health hazard”.
“What we want to do with this information is promote more action, more protection of workers,” she added.
Often, the deaths associated with working long hours occur much later in life than the shifts worked. The study found that most victims – 72 per cent – were men who were middle-aged or older.
The worst affected areas, meanwhile, were Southeast Asia and the Western Pacific region, a WHO-defined area which includes China, Japan and Australia.
The United Nations health organisation fears that the situation could be worsening further still, particularly amid the Covid-19 pandemic.
“The pandemic is accelerating developments that could feed the trend towards increased working time,” they said, adding that at least one in nine people currently work long hours.
ONS analysis showed that those who worked from home in 2020 worked an average of four more hours a week than those that did not, and that home workers worked an average of six hours unpaid overtime each week.
A poll conducted partway through the year found that two-thirds of Brits believe the government should explore the introduction of a four-day working week.
More than half of Conservative voters were in favour of the policy’s consideration, which was floated by the Green Party and the Labour Party in 2019.
Capping hours is, moreover, beneficial for employers as well as for workers as it has been shown to improve productivity, according to WHO technical officer Frank Pega.
“It’s really a smart choice not to increase long working hours in an economic crisis,” he said.
The WHO has said that it will seek to improve its own policy in the light of the study. Staff including its chief Tedros Adhanom Ghebreyesus say they have worked long hours during the pandemic.