Living by the Sun

For all of human history, our days were shaped by the sun. We woke with the dawn, spent our days outdoors in bright natural light, and wound down by the glow of a fire. In little more than a century, electric light has changed all that. Today, most of us spend around 90% of our time indoors, in light that is too dim by day and too bright by night. Our bodies have noticed.

Light is information

We think of light as something that helps us see. But light is also a signal that tells every cell in the body what time it is.

In 2002, scientists confirmed that the eye contains special light-sensing cells that have nothing to do with sight. They contain a pigment called melanopsin, which is most sensitive to blue light, the kind that fills a bright morning sky. These cells send messages straight to the body's master clock, a small cluster of nerve cells in the brain called the suprachiasmatic nucleus.¹

This master clock keeps time for clocks in almost every organ: the liver, gut, heart, muscles and fat cells. Together they decide when we feel alert or sleepy, when hormones rise and fall, when we digest best, and when the body repairs itself.² Light is the main signal that keeps them all in step. (See The Hormone Web.)

Light is a signal that tells every cell in the body what time it is.

Too dim by day, too bright by night

The body clock needs a strong contrast: bright days and dark nights. Modern life blurs the two.

• Our days are too dark. Even a cloudy winter morning outdoors can be ten times brighter than a well-lit office, and a sunny day a hundred times brighter. Indoors, the clock never gets a clear "daytime" signal.
• Our nights are too bright. Ordinary room lighting in the evening delays the release of melatonin, the hormone that prepares us for sleep, and shortens how long it lasts.³ Reading on a backlit screen at bedtime delays melatonin further, and leaves people sleepier and slower the next morning.⁴

A study from Colorado shows what happens when we live by the sun. Volunteers spent a week camping with no artificial light at all, only daylight and firelight. Their body clocks shifted around two hours earlier, so that their melatonin rose at sunset and they woke naturally near sunrise. "Night owls" and "larks" came into step with one another.⁵

What light does for health

When light patterns are out of balance, the effects reach far beyond sleep:

• Mood. In a UK Biobank study of more than 85,000 people who wore light sensors, those with more daylight had a lower risk of depression, while those exposed to more light at night had a higher risk.⁶ Bright light therapy is an established treatment for seasonal affective disorder (SAD), and has been studied for other kinds of depression too.⁷ (See Where Body Care Meets Mind.)
• Blood sugar and metabolism. In the same UK Biobank group, people with the most light at night had a higher risk of developing type 2 diabetes over the following years.⁸ When the body clock is confused, the body handles sugar less well.
• Hormones. Morning light helps set a healthy rise in cortisol, our "get up and go" hormone, which then falls in the evening. (See The Cortisol Clock.)
• Sleep. Bright days and dark evenings let melatonin rise on time, for deeper and more refreshing sleep. (See The Art of Sleep.)
• Children's eyes. Short-sightedness has risen sharply worldwide. In a trial in China, adding just 40 minutes of outdoor time to the school day reduced the number of children who became short-sighted.⁹

Sunlight on the skin

Light doesn't only work through the eyes. When sunlight touches the skin, it sets off several helpful processes. (See Skin Deep.)

Vitamin D. The skin makes vitamin D from the sun's UVB rays. It supports strong bones, muscles and a balanced immune system.¹⁰ In the UK, the sun is too low between October and March for the skin to make enough, so naturopathic nutritionists, in line with NHS advice, recommend that everyone considers a daily vitamin D supplement of 10 micrograms (400 IU) in autumn and winter, and all year round for people who rarely get outdoors or have darker skin.¹¹

Blood pressure. Sunlight releases nitric oxide stored in the skin, which relaxes blood vessels. In one study, half an hour of UVA light lowered blood pressure in healthy volunteers.¹²

A balanced view of the sun. Too much sun, and especially sunburn, raises the risk of skin cancer. But too little may carry risks of its own. A Swedish study following nearly 30,000 women for 20 years found that those who avoided the sun had a higher risk of death from all causes than those who spent more time in it.¹³ The researchers stressed that this kind of study can't prove cause and effect, but it suggests the healthiest path lies in sensible, regular sun rather than complete avoidance.

Red light and the morning sun

Early morning and evening sunlight are rich in red and near-infrared light, which reaches deeper into the body than blue light. Research suggests these wavelengths can support the mitochondria, the tiny power stations inside our cells. In a study at University College London, people over 40 who looked into a deep red light for three minutes in the morning improved their colour vision, which normally declines with age.¹⁴

Red light therapy panels are now widely sold. The research is early but interesting, especially for skin, healing and eye health. A free alternative is to step outside at sunrise or sunset, when the light is naturally rich in red. (Never look directly at the sun.)

Living by the sun: simple steps

• Get outside in the morning. Spend 10 to 30 minutes outdoors within an hour or two of waking, without sunglasses if your eyes are comfortable. Longer on cloudy days. A morning walk is ideal.
• Brighten your days. Work near a window, take breaks outside, and eat lunch outdoors when you can.
• Dim your evenings. After sunset, use lamps rather than bright overhead lights, and choose warm, amber bulbs. Candlelight is lovely.
• Mind your screens. Turn on night mode, lower the brightness, and try to put screens away an hour before bed. If you need to use screens in the evening, blue-light blocking glasses can help (see below).
• Make your bedroom dark. Use blackout blinds or an eye mask, and cover small standby lights.
• Enjoy the sun sensibly. Short, regular spells of sun on bare skin, especially arms and legs, without burning. Cover up or move into the shade well before your skin turns pink.
• Follow the seasons. In winter, it's natural to sleep a little longer and slow down. Make the most of daylight hours, and consider a light therapy lamp on dark mornings if your mood dips.

At Rootwise, we see light as one of the most overlooked medicines of all. It costs nothing, it's available every day, and it brings every system in the body back into rhythm. Before reaching for a remedy for tiredness, low mood or poor sleep, it's worth asking: how much daylight am I really getting?