Goodbye to the dark, dark night
When the first New York street bathed in the glow of electric light in 1879, it heralded a dramatic change in how our lives were structured. Taking control of the night allowed increased working hours, recreation and security.[1]
It’s almost impossible for modern humans to imagine a world without the blaze of artificial light. The Milky Way has become invisible to almost two-thirds of Europeans and 80% of Americans.[2]
Is there (pardon the pun) a dark side to our love affair with light? What are the health effects on humans (not to mention animals and plants) of artificial light at night (ALAN)?
An evolutionary perspective on night light
Before the boundaries of day and night becoming obscured, around 140 years ago, humans exposure to light at night was low. A full moon on a clear night provides 0.1-0.3 lux and a candle 1 lux (lux is a measurement of illumination). A modern living room at night is 100-300 lux.[2]
From an evolutionary perspective, it's a big leap in a short time. Has our physiology had enough time to adapt?
Light as pollution
Electric light is the fastest growing form of pollution, with an average rise of 3-5% each decade. It not only affects humans, it's also changing the way plants and animals live and reproduce.[3]
A circadian rhythm out of time
Various rhythms control our biological process. The best studied of these is the circadian rhythm. Left to their own devices, our body clocks would run to a slightly longer than 24-hour cycle.[4] Exposure to daylight keeps them in sync.
Our circadian rhythm works like this: Photons of light hit the retina in the eye and stimulates a nerve that carries a message the suprachiasmatic nucleus (SCN) in the brain. The SCN is like a conductor; it orchestrates the signals regulating your core body temperate, sleep/wake cycle and hormone production.[5]
The circadian rhythm is under attack from the modern world. The issue is two-fold. Too little light during the day and too much at night. There is no longer such a sharp contrast between night and day effectively has weakening and distorting (in the case of shift-work) our circadian signals.[6]
Colour temperature and wavelengths
It’s not just the level of illumination which is problematic. The colour temperature of the light is also significant. Although fluorescent, compact fluorescent and LED lights are energy efficient, they emit light in the blue spectrum which suppresses melatonin release.[2]
Effects of artificial light on sleep
Disruption of the circadian clock is most immediately noticeable on sleep. The result of repeated poor sleep quality insidiously starts to impact on blood sugar, hormones and reproductive function. This then flows on to issues with appetite, metabolic changes, reduced memory, focus and cognition, fertility, and increased cancer and heart disease risk.[7]
Melatonin
Melatonin is a hormone produced by the body to promote sleep. It’s released by darkness and inhibited by light. Melatonin essentially works by “switching off” physiological processes which keep you alert.[8]
It’s probably pretty obvious that bright, blazing light will chase melatonin away. But, what most people would consider dim lighting is also no friend to melatonin.
Research shows melatonin suppression is impacted by levels of light of greater than 5 lux. An average e-reader provides 30-50 lux and a night light about 40 lux.[2]
Sleep impacts of reduced melatonin caused by artificial light [1,6,8,9]
- Shallow sleep – less time spent in deep, slow-wave sleep
- Reduced growth hormone – increased ageing, interfering with fertility
- Metabolic dysregulation, sugar cravings, weight gain and increased risk of developing type 2 diabetes
- Increased night-time arousals or early morning awakenings resulting in fatigue and poor concentration the following day
- Delayed sleep onset results in “melatonin” hangover the next morning where you feel groggy
- Rapid eye movement (REM) sleep is decreased
- Increased anxiety
- Loss of dream consolidation (dreams help us cope better with psychological challenges)
- Increased risk of snoring and sleep-disordered breathing
Cortisol and artificial light at night
Conversely, melatonin’s opposing hormone cortisol is also impacted by artificial light, causing it to remain higher than it should. This dysregulates the hypothalamic-pituitary (HPA) axis and causes the following:[9]
- Problems going to sleep and staying asleep due to the suppressing effect on melatonin
- Increased risk of mood disorders (high cortisol is linked to certain types of depression and anxiety)
Other health issues associated with artificial light
Breast cancer
It has been observed that female shift-workers have an increased risk of breast cancer. One of the hypothesis as to why this might occur relates to the melatonin suppressing effect on oestrogen: Breast cancer risk is increased in women with higher lifetime exposure to oestrogen.[6]
High blood pressure
Melatonin causes an overnight drop in blood pressure. This decrease effectively gives your cardiovascular system a daily "rest". If this doesn't occur, it may contribute to hypertension.[9]
Obesity
Animal studies show indications of genetic changes causing altered appetite and feeding patterns.[1]
Impacts on plants and animals
The broader impacts of ALAN are now also being studied on wildlife and plants. Artificial light has been observed to prevent trees from adjusting to seasonal variations and alters the breeding cycles of animals. Human survival is interlinked with plants and animals, and these seemingly subtle shifts may have more significant consequences that are not yet apparent.[9]
What to do about it?
Night lighting is here to stay. It forms an essential part of modern lifestyles. We can’t all head off to the bush and live by candlelight. Most of us wouldn’t want to. The challenge is to find the balance. How we can get the benefits and limit the downsides of artificial light?
A role for government and public health
The big picture is that light pollution requires a high level approach. There are already urban planners and architects looking to address this issue by using street lights that direct light downwards, where it is needed, rather than up into the sky and using sensor-controlled night lights. Hospitals are also recognising the effects of light in ICU on patient recovery.
Individual actions
As an individual, you may have varying levels of control of your nighttime environment depending on if you are a homeowner or renter.
Things to consider for home buyers, builders or owners
- Types of light fixtures and fittings and installing dimmers
- Locating sleeping areas away from ambient street lights
- Timers/sensors on outdoor/security lighting
- Window coverings in bedrooms, such as blackout curtains or blinds
Things everyone can consider
During the night:
- Switch off bright overhead lights and use warm coloured, low-level lamp light at least 90 minutes before bed
- At least one hour before bed, stop using computer, tablets and smart phones
In the bedroom:
- Create the darkest possible environment
- Use curtains and blinds if installed
- Avoid using your phone as an alarm clock. Choose an old fashioned clock with a non-illuminated dial. If you keep your phone next to your bed position, it face down so that any notifications that light up the screen will not be as visible
- Go analogue with your night-time reading. Swap the tablets and e-reader for a paper book
- Remove, switch off or cover any standby lights on electronic equipment
- Use a sleep mask. These are useful if you have minimal control over your environment. They do take a little getting used to but once you do you’ll notice a difference in the quality of your sleep
During the day:
- Make time to get outdoors.
- Try and get a total of at least 60 minutes a day of exposure to daylight to keep your circadian rhythm in good shape. (This doesn’t mean you need to stand in the direct sunlight)
Conclusion
The old saying “as different as night and day” may not be so applicable in a modern world, but by knowing the potential health effects and making a few changes, we can enjoy the benefits of ALAN and limit the impact on our sleep and health.
References
- Chepesiuk R. Missing the dark: health effects of light pollution. Environews 2009;117(1):20-27. [Full text]
- Bedrosian TA, Nelson RJ. Timing of light exposure affects mood and brain circuits. Nat Publ Gr 2017;7(1): e1017. [Full text]
- Tähkämö L, Partonen T, Pesonen A. Systematic review of light exposure impact on human circadian rhythm. Chronobiol Int 2019;36(2):151-170. [Full text]
- Stevens RG, Zhu Y, Stevens RG. Electric light, particularly at night, disrupts human circadian rhythmicity: is that a problem? Philos Trans R Soc Lond B Biol Sci 2015;370(20140120). [Full text]
- LeGates T, Fernandez D, Hattar S. Light as a central modulator of circadain rhythms, sleep and affect. Nat Rev Neurosci 2015;15(7):443-454. [Full text]
- Cho Y, Ryu S, Lee BR, et al. Effects of artificial light at night on human health : A literature review of observational and experimental studies applied to exposure assessment. Chronobiol Int 2015;32(9):1294-1310. [Abstract]
- Cho C, Yoon H, Kang S. Impact of exposure to dim light at night on sleep in female and comparison with male subjects. Korean Neuropsychiatr Assoc 2018;15(5):520-530. [Full text]
- Haim A, Zubidat AE, Haim A. Artificial light at night: melatonin as a mediator between the environment and epigenome. Philos Trans R Soc Lond B Biol Sci 2015;370(1667):1-7 [Full text]
- Smolensky MH, Sackett-lundeen LL, Portaluppi F, et al. Nocturnal light pollution and underexposure to daytime sunlight: Complementary mechanisms of circadian disruption and related diseases. Chronobiol Int 2015;32(8):1029-1048. [Abstract]
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