If we took away the walls, the ceilings, the street lights, the screens and allowed our senses to guide us, we might rise with the sun and sleep when it sets. Artificial lighting and blackout blinds allow us to choose our waking hours – but is it good for us to stay up late under the glow of electric bulbs then sleep in late? On Sunday 26 March the clocks spring forward as we switch to British summer time. Here’s why we should make the most of the extra daylight.
Why is morning light so important?
The body’s 24-hour cycle – its circadian rhythm – is guided by light. “We developed under the open sky,” says Dr Christine Blume, a sleep scientist at the Centre for Chronobiology of the University of Basel. “So, our biological clock is especially sensitive to daylight.”
This function, sometimes referred to as the circadian pacemaker, is located in the suprachiasmatic nucleus (SCN) in the brain’s control centre, the hypothalamus.
The most important environmental time cue – or Zeitgeber – reaching the SCN is ambient light. “We get information about the time in the environment through our eyes,” says Blume.
Non-image-forming light-sensitive cells in the eye, says Blume, are what primarily connect our internal biological clock to the environment. “[They are] especially sensitive to short wavelengths, which we sometimes call blue,” she says.
Blue light has a very short, high-energy wavelength. This is what we see most of in the morning and throughout the middle of the day.
Morning light, says Blume, induces a “phase advance”. It sets the internal biological clock, speeding it up a little – helping you to become tired earlier in the evening.
In fact, morning light is so important that there is good evidence that it’s a potent antidepressant – sometimes as effective as pharmaceutical antidepressants.
Serotonin, often referred to as the body’s natural antidepressant, is produced when sunlight enters your eyes. The most commonly prescribed antidepressant medications are designed to increase serotonin levels in the brain. However, these medications can come with numerous side-effects, ranging from anxiety to diarrhoea to sexual dysfunction.
Using daylight to treat depression, on the other hand, doesn’t have such side-effects. Morning light therapy has been shown to be beneficial in the treatment of seasonal affective disorder (Sad), perinatal depression, bipolar depression, eating disorders and attention deficit hyperactivity disorder (ADHD).
Studies have also shown that exposure to morning light significantly improves alertness and mood. It can reduce chronic pain, boost energy levels and mental performance, and result in better sleep.
In the evening, when the sun nears the horizon, the blue light waves are scattered in the atmosphere – and longer, redder light waves reach the surface of the Earth. It is at this time that the master biological clock initiates the production of melatonin, a hormone that promotes sleep.
So, our circadian rhythm aligns our sleep and wakefulness with day and night – creating a healthy cycle of restorative rest that enables increased daytime activity.
How daylight can help you sleep
Getting enough natural light during the day is critical for quality sleep at night – and sleep is essential if you want to function in the day. When you sleep, your brain forges new thought connections and memories are consolidated. Without sleep, your ability to concentrate, learn and remember is impaired.
Sleep deprivation affects the processing of emotional memory, too, resulting in a tendency to select and remember negative memories after inadequate sleep. A lack of sleep is associated with mental disorders such asbipolar disorder, anxiety and depression.
Your immune system is also reliant on sleep. While you sleep, it produces protective, infection-fighting antibodies and cytokines. Sleep deprivation prevents it from building up these defences, so your body may not be able to fend off invaders, and recovery from illness can take longer.
A disrupted circadian rhythm is associated with a range of health problems including cancer, cardiovascular dysfunction, reproductive problems and neurodegenerative diseases such as dementia.
Appetite, hormones, immune function: daylight helps regulate them all and more
This daily cycle regulates not just our sleep and wake patterns – but also digestion, hormonal activity and other vital body functions.
“We have one biological master clock, which I like to think about as a conductor of an orchestra,” says Blume. “And we have other clocks, for example in the liver, heart and skin – basically in every single cell in the body.”
These trillions of tiny clocks are our natural timing devices, regulating physiological functions throughout the body over the course of about 24 hours.
So, if you mess up your master clock, you mess up all the other daily functions too.
Take appetite, for example. Have you ever noticed you feel hungry when you’re tired? There is mounting evidence linking a lack of sleep to weight gain and obesity.
Hormone production is dependent on sleep. Two of these hormones are leptin, which tells your brain that you’re full, and ghrelin, the “hunger hormone”. A lack of sleep has been found to decrease levels of leptin and increase ghrelin, prompting you to eat more than you really need to.
I’m a night owl, should I force myself to rise with the sun?
“People often think they are either larks or owls but most of us are somewhere in between,” says Blume. True owls, explains Blume, are those who suffer from “delayed sleep phase syndrome”.
“They can’t go to sleep before 2am or even later and, for them, waking at 8am feels like getting up at 5am for the rest of us.”
Most of us merely have an owlish tendency. We’d rather go to bed late and get up at 8am instead of 6.30 – but it’s fairly easy to retrain our circadian rhythm by restricting light in the evening and going to bed earlier.
“Nature came up with something that allows us to synchronise with the outside world,” says Blume. “Our bodies and the world communicate. Your chronotype is an interaction between genetics and light exposure, so behaviour. You can adjust to some extent.”
But I can lie in at the weekend, right?
The problem comes at weekends when we have the freedom to sleep when we want. Often we shift our circadian rhythm towards later times – which can lead to bleary-eyed Monday mornings.
“We call this mismatch between societal and internal biological rhythms ‘social jet lag’,” says Blume.
Blume recommends making sure you get lots of natural light in the morning and avoid artificial light in the evening to advance the biological clock, effectively resetting it to a more socially acceptable timetable.
And, says Blume, getting outdoors is key. On a bright summer day, you can easily have 100,000 lux (the measure of light level intensity). That’s around 200 times standard lighting you might experience indoors.
“Even on an overcast day, the light is much brighter outside than in,” says Blume. “We often underestimate the brightness of daylight.”
Being outdoors brings other benefits too. Vitamin D – the “sunshine vitamin” – is produced when sunlight hits the skin. This vitamin helps the body absorb and retain calcium and phosphorus – important for building bone. It has also been found to reduce cancer cell growth, help control infections and reduce inflammation.
Plus, as little as 10 minutes in a natural setting has been shown to increase feelings of happiness, reduce stress and improve focus. And spending time outdoors may reduce loneliness, improve immune function – even protect your eyesight.
So, when the clocks spring forward, should we get up and out – and look after our biological clocks?
“This is something free and natural,” says Blume. “I always recommend natural daylight.”
Go for that walk or run or cycle first thing in the morning and avoid the blue lights of screens in the evening – you’ll sleep better at night and feel better for it.
