Been spending a bit too much time indoors? You’re not the only one. Many of us now spend up to 90 per cent of our lives indoors and our retinas are bombarded with artificial light late into the evening.
That means compared with our ancestors, we’re exposed to less light during the day and more light at night. This disruption to the light-dark cycle we evolved with is having a profound effect on our circadian rhythms, shifting sleep patterns and affecting our health way more than we might realise.
Light levels help to regulate alertness and mood. We also rely on sunlight to convert cholesterol in the skin into vitamin D, which helps build strong bones, and plays a beneficial role in our immune system. Some headlines even suggest that sunlight could and help protect us from the coronavirus. But does the science back that up? And what do we miss when we’re confined indoors?
Hey, it’s me…the sun. Haven’t seen you for a while. Been spending too much time indoors? Let’s get reacquainted.
Before the invention of houses, street lights and Netflix, our ancestors spent most of their days outside, and their nights were illuminated by nothing brighter than firelight.
Now we spend 90 per cent of our lives indoors, and our retinas are bombarded with artificial light late into the evening. This affects our sleep, our biology and our health way more than we might realise.
The good news is that a little daylight goes a long way. But what does sunlight do for us, and what do we miss when we’re stuck indoors?
Our bodies are guided by circadian rhythms, 24-hour cycles in our biology and behaviour that make us feel alert during the day and sleepy at night.
These rhythms are regulated by a special set of cells at the back of the eye, behind the rods and cones that enable our brains to construct images. They are called intrinsically photosensitive retinal ganglion cells, or ipRGCs for short.
ipRGCs are particularly sensitive to light in the blue part of the spectrum, including bright daylight, and the light from our screens. They send signals to areas of the brain that control alertness. Just one hour of low-intensity blue light can increase reaction speeds as much as drinking two cups of coffee. That’s great if your aim is to be awake, but not so good just before bedtime.
So if you’re watching this in bed… stop it! Hit like and subscribe and come back tomorrow morning.
Exposure to sunlight in the mornings helps to keep your circadian rhythms working properly, and it has been linked to better sleep quality and lower depression scores. The same ipRGCs that feed into the brain’s master clock also connect to the thalamus, a brain area related to mood.
And there’s another important reason to be getting plenty of sunshine: vitamin D. When sunlight hits your skin, it converts cholesterol into vitamin D, which helps build strong bones, and plays a beneficial role in our immune system.
Hospital patients have been shown to recover faster when they have more access to daylight, and researchers think it may increase the number of immune cells that rally to an injury.
There’s also some evidence of a link between levels of vitamin D and some viral infections, including the flu and covid-19. But this isn’t clear cut.
One small study found that people in hospital with covid-19 were much less likely to need intensive care if they were given high doses of vitamin D. On the other hand, another study compared vitamin D levels in people who tested positive for the coronavirus with those who didn’t, and found no difference.
We’ll learn more from randomised, controlled clinical trials that are currently under way, but for now the evidence that vitamin D supplements can prevent severe illness is pretty weak.
But the importance of vitamin D for our bones isn’t in doubt and many of us simply aren’t getting enough. This is especially pronounced in the winter months, when there isn’t enough sunlight to produce the vitamin in our skin, particularly for people in higher latitudes and those with dark skin tones. And so, if only to support strong bones, most people in countries like the UK should take a standard vitamin D supplement every day through the winter months.
Clearly, sunlight is very important for us, and even small increases in your exposure can improve sleep, mood and recovery from illness. And there are some easy things we can all do to get more of it.
- Do some exercise outdoors every day, even if it’s just going for a walk.
- Wake up at a regular time and open the curtains as soon as you get up.
- Change where you sit so you’re closer to a window. Even a small distance can have a dramatic effect on light levels.
- Use dimmer light in the evenings. You can even buy colour-changing bulbs so you can benefit from blue-light during the day and warm-coloured light in the evenings.
- Listen to your body and go to bed when you start feeling sleepy.
- Use blackout blinds to block the light from street lamps.
- Cut down on your screen time before bed.
It sounds obvious but just go outside as much as you can.
There is still much to learn about how light and darkness affect our biology. Yet as a basic principle, we should all be striving to brighten our days and darken our nights. We evolved on a planet with a 24-hour cycle of day and night. It is time to reconnect with those extremes.