In September 2015 the sleep researcher Paul Kelley, then an honorary clinical research fellow at the University of Oxford's Sleep and Circadian Neuroscience Institute, told the British Science Festival that most adults would be better off starting work at around 10 a.m. His argument was that early starts clash with the body clock and leave much of society chronically short of sleep. The short answer to whether "nature wants us to start at 10" is more nuanced: body clocks really do differ, and many people are sleep-deprived, but there is no single start time that suits everyone.
What Kelley actually proposed
Kelley's talk was reported widely under headlines calling a 9-to-5 day "torture". His underlying point was more specific. He said that people's internal 24-hour rhythms cannot simply be retrained to suit a timetable, and that schedules built around early mornings leave many people working while their bodies still expect to be asleep. In his words, as reported by The Guardian and others: "We cannot change our 24-hour rhythms."
He linked the problem most strongly to young people. According to Kelley, the 14 to 24 age group is more sleep-deprived than any other part of society, and British teenagers lose around ten hours of sleep a week because of early lessons. His suggested timetable was age-based:
- children aged 8 to 10: start around 8:30 a.m.;
- 16-year-olds: start around 10 a.m.;
- 18-year-olds and university students: lessons from about 11 a.m.;
- adults in general: work starting around 10 a.m.
He also pointed out that staff, not only pupils, are usually sleep-deprived, which is why he extended the idea to the working day.
How the body clock works
Almost every cell in the body follows a roughly 24-hour cycle known as the circadian rhythm. A master clock in the brain coordinates it, and it is kept in step mainly by light. Light reaching the eyes in the morning signals daytime and helps trigger the release of cortisol, which prepares us to wake. In the evening the hormone melatonin rises, promoting sleep, and it peaks in the early hours. Bright light late at night, including from phones and tablets, can suppress melatonin and make it harder to drop off.
The timing of this clock is not the same for everyone. Researchers describe each person's natural preference as their chronotype. Most people sit somewhere between strong "larks" and strong "owls", and normal differences can shift a person's ideal sleep window by two to three hours. Chronotype is partly inherited, with more than 20 genetic variants linked to it, and partly shaped by light, meals, social life, work and school.
Why age changes everything
The strongest part of Kelley's case is about age. Young children tend to sleep and wake early. During adolescence the body clock shifts later, so it is natural for many teenagers to feel alert late in the evening and groggy at 7 a.m. That is biology, not laziness. In later life the pattern swings back: older adults usually sleep a little less, wake earlier and may find it harder to stay asleep.
This is why the debate about later starts has mostly focused on schools. A 16-year-old dragged out of bed for an 8 a.m. lesson may be waking at what, for their body, feels like the middle of the night. Kelley had previously been head teacher of Monkseaton High School in North Tyneside, which experimented with a 10 a.m. start, and he was involved in a later UK research project, Teensleep, that set out to recruit 100 schools to test later start times.
Does a 10 a.m. start make sense for workers?
The case for adults is weaker but still interesting. In the United States, Pew Research Center found that in early 2015 millennials, then aged 18 to 34, had become the largest generation in the labour force, at about 53.5 million people, more than one in three workers. Many in that age range are still at the later end of the chronotype curve, so an early start may suit them less well than it suits older colleagues.
On the other hand, a fixed 10 a.m. start would not suit everyone. Larks would lose productive morning hours, parents would still face school schedules, and many jobs, from healthcare to transport, have to run around the clock anyway. What the research really supports is flexibility: letting people align their working hours more closely with their own sleep needs where the job allows it.
Some employers already do this through flexitime or core hours, where everyone overlaps in the middle of the day but can choose when to start and finish. Remote and hybrid work, which spread widely after 2020, has made this easier in many office jobs.
What short sleep does to health
Whatever time you start work, getting too little sleep matters. Insufficient sleep has been linked in research to low mood and depression, higher risk of obesity, poorer concentration and, in teenagers, more risk-taking such as substance use. Tired people also make more mistakes and are more likely to have accidents, especially when driving.
Most health organisations recommend that adults get at least seven hours of sleep a night, with teenagers needing more. If you regularly struggle to sleep, wake unrefreshed, or feel exhausted despite enough time in bed, talk to a doctor, as conditions such as sleep apnoea and insomnia are common and treatable.
Practical ways to work with your body clock
- Get morning daylight. Spending time outside soon after waking is one of the most effective ways to nudge your clock earlier.
- Dim the evening. Lower lights and limit screens in the last hour before bed so melatonin can rise.
- Keep a regular wake time. Large differences between weekday and weekend wake-up times act like a weekly mini jet lag.
- Ask about flexible hours. If you are a natural owl, even a 30 to 60 minute later start can make a difference. Many employers will consider it if productivity stays the same.
- Protect sleep for teenagers. Parents can support later bedtimes being matched with realistic wake times, and limit late-night devices rather than fighting biology.
Kelley's 10 a.m. idea is best understood as a provocation rather than a law of nature. Its real message is that timetables should be designed with human biology in mind, not the other way round.
Sources: ScienceAlert, 9 September 2015: Work shouldn't start until 10am, says sleep expert; Pew Research Center, 11 May 2015: Millennials surpass Gen Xers as the largest generation in the U.S. labor force; NHLBI: Your sleep/wake cycle; Wikipedia: Chronotype. Story first reported by HuffPost and shared via Expanded Consciousness.
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