Sleep is critical for physical and mental health, and our quality of life. While 3% of the population are genetically programmed to function with less than six hours sleep regularly, the rest of us need around 7.5 hours a night. But what determines whether we like to go to bed early or late?
What happens when we sleep?
Within a 7.5-hour-long sleep, the average person will complete five 90-minute sleep cycles.
The first few cycles concentrate on cleaning and maintaining our body, heart and brain. Our brain then files the information taken in during the day to consolidate our knowledge and learning.
Later, our REM (rapid eye movement) cycles allow the brain to play – creatively combining unconnected information and ideas (called abstraction), and targeting memory, plasticity and building new brain (neurogenesis).
Larks and owls
Our internal body clock is set via a combination of biology (nature), light exposure and social scheduling (nurture).
Biologically, people sit on a bell-curve of “morningness and eveningness”. Around 10% of the population are morning larks, and 20% true night owls.
Light stimulates the hormone melatonin in the morning and shuts it off at night, leading to changes in energy levels, hunger, stress response, body temperature and the stress hormone cortisol.
While some of our preferences for going to bed early or late is programmed, our actions can also influence our patterns.
Larks consistently report higher levels of happiness, healthiness, productivity and well-being, with less stress and depression levels than owls.
One theory is larks have a greater feeling of choice and control over their mornings as they wake up before they have to rush off to the accepted work or school start times. Instead they can relax, eat, work (without interruption) or exercise.
Exercise is a common differentiator in that larks generally get more of it. But interestingly, the more owls exercise, the less differentiation in levels of stress, depression and well-being between the two types.
Some German research has also found structural differences in the brain of the night owl. Late sleepers were more likely to have abnormalities in the white matter of their brain, which is associated with depression.
However, larks don’t get it all their way. Although owls consistently report lower well-being, higher stress and lower physical activity, studies routinely describe owls as smarter, more outgoing, good humoured and more creative than larks.
At societal level, some countries even shape such things as cross-border projects to fit an observation that people from countries that prioritise punctuality over sleep are more efficient, whereas those with relaxed timekeeping, which better suits owls, are more creative.