Over tens of thousands of years our bodies evolved an exquisitely reliable metronome, a biological clock tuned to one of the most basic certainties that unites all life on this planet: that night follows day follows night. But then we started to mess with it.
Many of us now live in a world of 24-hour possibilities. Whether it’s to work or party, or simply squeeze more hours out of the day, with artificial lighting humans have reclaimed the night. And what is becoming increasingly clear is that this love affair with light is having a profound effect on our emotional, physical and mental well-being.
Only in the last decade or so has science begun to grasp just how light affects the body. While these discoveries are a warning to us all, they also provide an opportunity. Understanding the deep-rooted relationship between light and health, and the way modern technology interferes with it, might enable us to apply the same technology to make us all feel a little bit brighter.
The internal body clock is regulated by a group of around 20,000 neurons, which form the suprachiasmatic nucleus, or SCN, a small region of the brain located in the hypothalamus. The SCN controls the body, like a silent metronome, in response to nerve impulses from the eye, which are triggered by daylight. The SCN orchestrates the release of hormones like cortisol to make us more alert, and changes in body temperature to finely tune our physiology and psychology to meet the needs of the progressing day.
Heart disease and diabetes
“Light at night time is a recent event in human evolution, so biologically we are still in an early stage as to the effects of night-time light on humans,” says Cheng Chi Lee, who studies circadian rhythms at the University of Texas Medical School. Studies have found that working night shifts is linked to a higher risk of various health problems including some forms of cancer, heart disease and type-2 diabetes. Women who do shift work or work as flight attendants continually crossing time zones have been shown to have a 50 per cent increase in the risk of breast cancer.
It is not entirely clear what causes all these effects on health. Part of the problem is disrupted sleep, which is known to be important for recovery and repair of the body, memory consolidation and possibly even detoxification of the brain. Another issue is that these people tend to eat more at night, when the body is maladapted to deal with food. This causes spikes in insulin, which may explain the link to diabetes. You don’t even need to work the night shift to see the effects. One study, in which volunteers read from either an iPad or a book each night before bed for two weeks, found that the iPad delayed production of melatonin – the hormone that tells our body it is night – by an hour and a half on average. After reading from the iPad, participants also had less REM sleep, which is important for memory consolation, and felt more tired the next day.
BLIND SIGHT One recent discovery is that the eye has, in addition to rods and cones (the receptors that sense colour and light), a third type of receptor that detects light not for vision but as a cue to train the circadian rhythm. This idea was put forward by Charles Czeisler, a sleep researcher at Harvard Medical School, in 1995 after he conducted research on blind people, showing that shining light into their eyes at night shifted their body clock even though they couldn’t perceive the beam.
These people were blind because they had lost their rods and cones. But no such effect is seen on patients who have had their eyes removed, because in doing so they had also lost these crucial light-sensing, retinal ganglion cells. These people are unable to synchronise their biological clock to a 24-hour day, so it shifts gradually over time, resulting in a condition called non-24-hour sleep-wake disorder. This causes them to experience periods of extreme sleepiness during the day and insomnia at night. “It is as if they are jet-lagged all the time,” says Czeisler’s colleague Charles Weitz, who studies mammalian circadian clocks.
Light affects emotions, too. Most of us have experienced feeling brighter on a sunny day, and more than 12 million people across northern Europe are thought to suffer from Seasonal Affective Disorder – episodes of depression during the winter months – when their exposure to daylight plummets. But light seems to affect all of us in subtler ways. In one experiment, Gilles Vandewalle and colleagues at the University of Liège, Belgium, scanned the brains of volunteers as they listened to meaningless words spoken in either a neutral or angry voice while they were exposed to blue or green light. Brain areas that process emotion showed a stronger response to the angry voice compared to the neutral one, but the response was even stronger in the presence of blue light, to which our photoreceptors are more sensitive. Other research by the team found that exposure to orange light can help boost alertness and memory.
Several companies are already cashing-in on these ideas, with smart LED bulbs that can change colour in your home as the day progresses or be controlled by an app depending on your mood. Others are coming up with personal devices aimed at helping people gain better control of their internal clocks. Wearable devices such as Re:Timer or Ayo glasses use LED lights which emit in the green and blue spectrum to which our eyes are particularly sensitive, to help counter the effects of jet lag, provide an energy boost, or even help people become more of an early bird or night owl.
But what if we could use clever lighting to help lift peoples’ mood not just at home but in social settings? That’s the idea behind the De-escalate project launched at the end of last year by the Intelligent Lighting Institute at the Eindhoven University of Technology (TU/e). To understand the effects of light on behaviour, they tested how warm or cool lighting affected interactions at an on-campus canteen. They found that people chatted more, were more polite, and laughed more in warm lighting.
Street lights and beer sales
An even more ambitious goal is to use light to reduce aggressive behaviour. The TU/e researchers have turned a busy bar street in the city into a living laboratory. Every weekend over the next two years the street lighting will change in colour and intensity, using specially designed LED lamps. The team will collect a range of data, including the number of visitors, sound levels, beer sales and social media activity, and then compare them with police records. Every year the street sees several hundred incidents ranging from vandalism to assault, so the idea is to test whether light might play a role in creating a less aggressive environment.
Workplaces could benefit, too. Marilyne Andersen, dean of the School of Architecture at EPFL, is working on ways to design buildings that take into account the discoveries about the importance of light on health. That’s easier said than done. For a start, the effects are not instantaneous – unlike, say, too much glare shining in your eyes. “The effect will be based on what the light exposure was in the last four hours, but also the day before, the sleep-wake cycle of the person, the spectrum and pattern of the lights,” she explains. “All these have very different effects.” To address the issue, Andersen’s team is building a mathematical model which any architect could use to compare how different design options affect the health of people using the space
Such technologies are already starting to shape our relationship with light for the better. But there’s also a time-tested way to feel the benefits. Whenever you can, get an early night, switch off, and enjoy the dark. Who knows, you might come to appreciate your body in a whole new light.
By Catherine de Lange @catdl