Nocturnal "night owls" are more at risk of dying than "morning larks" who turn in early and leap out of bed when the sun rises, according to new research in Britain.
Scientists who studied a population of nearly half a million Britons found that over a six-year period, night owls, who stay up late but struggle to drag themselves out of bed in the morning, had a 10% greater risk of death than early birds.
The difference held true even after adjusting for expected health problems in night owls, such as metabolic dysfunction and heart disease.
Society should wake up to the real difficulties faced by night owls, said the researchers. They called on employers to be more flexible towards staff who suffer when forced to clock in early.
Dr Kristen Knutson, a member of the team from Northwestern University in Chicago, said: "Night owls trying to live in a morning lark world may have health consequences for their bodies.
"They shouldn't be forced to get up for an 8am shift. Make work shifts match people's chronotypes. Some people may be better suited to night shifts."
The study, published in the journal Chronobiology International, found higher rates of diabetes, mental disorders and neurological conditions among night owls.
The researchers drew on data from the UK Biobank, a storehouse of medical and genetic information provided by 500,000 people aged 40 to 69 from across the UK.
British co-author Professor Malcolm von Schantz, from the University of Surrey, said: "This is a public health issue that can no longer be ignored.
"We should discuss allowing evening types to start and finish work later, where practical. And we need more research about how we can help evening types cope with the higher effort of keeping their body clock in synchrony with sun time."
Larks are better able to adjust their body clocks to the light and dark rhythms of the rising and setting sun, said the researchers.
Owls may have a body clock that fails to match their external environment, said Dr Knutson.
Being a night owl was associated with psychological stress, eating at the wrong time, lack of exercise, lack of sleep, and drug or alcohol use.
Genetics and the environment played roughly equal roles in determining whether you are a night or morning person, said the scientists.
One way night owls could help themselves was to ensure they are exposed to light early in the morning, but not at night, according to Dr Knutson.
They should try to be disciplined about bed-times and get jobs done early in the day rather than leaving them until late, she said.
Dr Knutson added: "You're not doomed. Part of it you don't have any control over, and part of it you might."