It’s time to see the LIGHT on the blight that harms us all
It could cause diabetes, weight gain and even cancer. Alarming new research into light pollution reveals why ...
VIEWED from space, the Earth at night is a beautiful sight: the lights of our towns, cities and road networks forming a dazzling web of gold and silver. Artificial light has been credited with reducing crime and boosting industrial growth, as well as letting us work and play for longer. Yet could it also be wreaking havoc on our health?
Some experts — and a growing body of research — suggest it is, with our overly-bright, artificially lit lives contributing to modern epidemics such as diabetes, obesity and even cancer. And this isn’t just about our own habits — using glowing mobile phones late at night, for instance — light pollution from street lamps, car lights and shopfronts lit up around the clock could also have a harmful effect.
‘Electric light allows us to override the natural light- dark cycle,’ says Professor Steven Lockley, a neuroscientist at Brigham and Women’s Hospital in Boston, Massachusetts, who studies the effects of light on our bodies. ‘It means we can do things like work or socialise when it’s dark, but our biology suffers because really, any light after dusk is unnatural.’
‘I am persuaded that circadian disruption from electric lighting is contributing to breast cancer, and not only that, but to obesity, diabetes, and depression,’ adds Professor Richard Stevens, a cancer epidemiologist at the University of Connecticut, who studies the links between artificial light and health. NOT JUST A PROBLEM FOR BIG CITIES Light pollution is excessive or inappropriate artificial light at night. It comes from many sources: from lightbulbs, TV screens, tablets and smartphones in the home — and from street lights, cars and floodlighting outdoors.
If artificial lighting continues to expand at its current rate, scientists predict that twice as much of our planet’s surface will be illuminated by 2050, compared to six years ago. A study published in Science Advances in 2016 found that 83 per cent of the world’s population, and some 99 per cent of people living in Europe and North America, now live under light-polluted skies — in other words, this isn’t only a problem for those who live in big cities.
Although some areas of the UK, such as Northumberland, Snowdonia, Exmoor and north-west Scotland still have extremely dark night skies, our cities, and a chunk of England stretching from London up to Liverpool and across to Leeds, are so bright that many of the stars are invisible to us.
The obvious problem with light pollution and too much artificial light in our homes is that it can stop us sleeping. According to a study published in the journal Sleep in 2016, people living in areas with higher levels of light pollution (as recorded using satellites) went to bed later, slept less, and experienced poorer-quality sleep.
Modern street lamps may be a particular problem. In 2016, the American Medical Association (AMA) voiced concerns about the increased prevalence of LED street lights, which, although they appear white, give off a lot of light in the blue part of the spectrum — which is the type most disruptive to our body clocks.
‘It is estimated that white LED lamps have five times greater impact on circadian sleep rhythms than conventional street lamps,’ the AMA said. Professor Stevens shares these concerns. ‘There is a global effort to roll out these very bright LED lights without adequate vetting of how it might affect human health and ecology,’ he says. The AMA advised that street lights should ideally be dimmable, be installed with shields around them to reduce the amount of light reflected upwards into people’s bedrooms, and use bulbs that produce a warmer white light, rather than the standard, cold blue-white light.
Light pollution isn’t only a problem because of its potential to affect our sleep. Animal studies have repeatedly suggested that exposure to even dim light at night, such as you might experience from bright street lights outside your bedroom window even when your own lights are off, can disrupt the activity of genes that drive our body clocks. The result is a flatten-ing in our daily biological rhythms that control everything from metabolism to mental alertness and the immune system.
In short, our bodies are confused and stop working as they are designed to, opening the door for all kinds of diseases to take hold.
IS YOUR BEDROOM MAKING YOU FAT?
WHILE research into levels of light pollution and corresponding rates of disease is still in its infancy, experts know that repeatedly confusing the body clock can raise the risk of diseases such as type 2 diabetes, depression and cancer.
This is based on large studies involving night shift-workers — who are regularly exposed to bright light at night — and who have been shown to have higher rates of these conditions, as well as obesity.
If light pollution similarly disrupts the body clock — and emerging research suggests it can — it could also raise the risk of these conditions. ‘ Associations have been reported for high disease burden in places with greater satellite- derived light levels at night,’ says Professor Lockley. For instance, a 2016 study in the International Journal of Obesity, which combined satellite images of night-time illumination with obesity rates, found that people in more brightly-lit areas tended to be heavier, even after taking into account factors such as wealth, which might influence obesity.
Another study, published in the Journal of Clinical Endocrinology and Metabolism the same year, found that elderly people in Japan who were exposed to higher intensities of light at night tended to have larger waists. When the same group was followed up 21 months later, the individuals who
were exposed at night to light equivalent i l tt to what ht you might i ht get t from street lights if you don’t have thick curtains in your bedroom, or from a nightlight, were more likely to have grown fatter.
Studies in mice have also suggested that exposure to low levels of light overnight — again, equivalent to a street light coming through thin bedroom curtains — is associated with greater weight gain compared to spending the night in darkness, even if the same number of calories is consumed.
And it’s not just obesity: a study published p blished i in C Current e t Biolo Biology in 2016, found that mice exposed to constant light — equivalent of a dimly lit room — at night experienced a reduction in bone density, increased muscle weakness, and tissue inflammation, which is associated with accelerated ageing.
WHY TOO MUCH LIGHT IS BAD
Our biology is designed to work according to set periods of light and darkness (day and night). In each of our cells there ticks what is called a ‘circadian’ clock, made up of a cluster of molecules, which drives daily fluctuations in our hormones, temperature and behaviour, preparing us for regular events such as getting up or going to sleep.
Sunlight helps to keep these clocks synchronised, both with the time of day and with each other, by activating cells at the back of our eyes which connect to the brain’s master clock. The problem pro is that these cells also respond resp to artificial light — and this has a knock-on effects on all kinds kind of cells in our body.
‘If we repeatedly tell the brain it’s daytime when it’s really night, all our circadian rhythms are going goin to get out of sync,’ says Professor fess Lockley.
Our Ou body is better at processing glucose gluc (sugar from food) during the daytime, for instance, because of coordinated c efforts by the pancreas, pan liver, muscle and fat cells, cell all of which receive signals from the master clock.
If the t insulin-secreting pancreas is no n longer in sync with the liver, or with w clocks in the fat cells and muscles, mus then our body’s ability to burn energy from food efficiently effic will become impaired, resulting resu in diseases such as type tytype 2 diabetes or obesity.
‘We ‘W think that this is one of the mechanisms mmec by which the risk of chronic chhro diseases such as diabetes is increased,’ Professor Lockley explains. ex Alterations in cellular clocks cl may also lead to abnormal cell ce growth and altered levels of circulating ci hormones that drive the th growth of certain cancers, including in breast cancer. WHAT ABOUT WOOD FIRES? PrIOr to the invention of gas and electric lighting, our only so source of artificial light was fire an and candlelight — and these do n not have the same effect on our b body clocks.
The brightness of light is measured in a unit called Lux. The amount hitting the back of the h eye on a moonlit night is ap approximately 0.3 Lux; a metre aw away from a flaming candelabra is m more like 0.6 Lux. A room with el electric lighting exposes you to ar around 100-300 Lux and a street la lamp leaking through bedroom cu curtains may be around 3 Lux.
Yet it is difficult to put a precise number on how much (or how little) l light you can be exposed to before it starts to have a negative impact m on health. This is because th the wavelength of the light, which af affects its colour, also matters — a as does how close it is to our eyes.
Our body clocks are most responsive to — and therefore most easily disrupted by — light in the blue part of the spectrum, of which daylight provides a hefty dose, but which is also in LED and fluorescent bulbs.
Firelight, by contrast, contains little short wavelength blue light, and lots of longer wavelength red light, which the circadian system is less responsive to.
The time of day also has an impact on our response to different types of light.
However, ‘ I’m confident in saying this,’ says Professor Stevens. ‘Wood fires and candles do not disrupt circadian physiology. I’m not going to go back into a cave with a wood fire for light, but we are way overlighting our environment.’
To work out the effect a light source may be having on our body clocks, scientists often measure levels of the hormone, melatonin, which is released in the evening in response to a signal from the master clock — and which is suppressed in bright light.
‘Melatonin is like a biological signal of night, telling our various organs and tissues it’s night-time,’ says Professor robert Lucas, a chronobiologist at the university of Manchester, who studies how light affects the body.
If melatonin is suppressed, it
suggests that the biological clock is being affected, too.
the bad news is that light levels equivalent to those in an artificially lit home (around 135 Lux) are bright enough to suppress melatonin, according to a study published in the Journal of Pineal Research in 2012.
HOW THE EXPERTS PROTECT THEMSELVES
ALtHOUgH night-time light exposure has the potential to disrupt your internal clocks, Professor Lucas cautions against trying to live in complete darkness after sunset.
‘it is likely to be more dangerous to keep the lights off and risk falling down the stairs,’ he says.
However, most circadian biologists have dimmer switches on the lights at home and try to dim them after sunset, as well as avoiding using electronic devices in the run-up to bedtime.
‘We can’t put an exact number on it, but light during the evenings should be dim and longer wavelength, so towards the red end of the spectrum,’ says Professor Stevens.
‘if you’re buying lightbulbs, choose ones that emit a warmer, yellowish light, rather than cool blue-white light.’
technology and gadgets may also help — from ‘smart lightbulbs’, which can be dimmed and colour-adjusted using an app on your phone, to glasses that block blue light (see box on previous page).
However, such measures won’t protect you against the menace of outdoor light pollution from street lamps at night. For this you need to use blackout blinds or curtains.
there may yet another way to make yourself less vulnerable to light pollution: ‘the effects of light in the evening highly depend on the light you were exposed to in the morning,’ says Dieter Kunz, a psychiatrist and sleep researcher at St. Hedwig Hospital in Berlin.
in a study published in neuropsychobiology last year, he found that exposing people to bright light for several hours in the morning negated the impact of blue light exposure in the run-up to bed, as well as boosting mental alertness throughout the day.
Daylight is far brighter than indoor light: even on an overcast winter’s day, the amount of light hitting our eyes is around 2,000 Lux, while on a cloudless day in summer it could be 100,000 Lux, compared to 100-300 Lux in an artificially lit room.
this means that spending more time outdoors — ideally as soon after waking as possible, when our brain’s master clock is more responsive to light — may boost our health by strengthening the amplitude of the circadian rhythm.
We evolved on a rotating planet, when the day was day and the night was night: it’s time to re-embrace those extremes.