Our hunter–gatherer ancestors didn’t have LED lights, iPads or street lights ablaze all night. Instead, they were dependent on the sun, the moon and fire for light. Consistent light cycles ensured that circadian rhythms, moods and hormones were in check.
But today, it’s a different story. We’re exposed to bright lights well past sunset, and during the day, we often don’t get enough real sunlight. Light can increase our productivity, but too much light has consequences. Artificial light at the wrong times creates a mismatch between your genes and the environment, with potentially dire health outcomes.
Reducing your exposure to light pollution can protect you from those negative health outcomes and help you sleep more soundly and feel more energized. Find out how to reduce light pollution and why it’s an important part of an ancestral health-based lifestyle.
Light Pollution: Too Much of a Good Thing
Humans have evolved alongside 24-hour day/night cycles, and our bodily functions have synced up with these cycles in what we call circadian rhythms. Most endocrine hormones exhibit a recognizable daily rhythm, including:1,2,3,4
These hormones regulate daily patterns of bodily processes like digestion, metabolism, and sleep.5,6,7 For example, cortisol should be highest in the morning to keep us alert and gradually decrease throughout the day, while melatonin should be highest at night to encourage sleep and low during the day. In fact, exposure to bright 480-nm light in the morning helps determine when the pineal glands will start releasing melatonin at night.8
Light, at the appropriate times and intensities, is the most potent regulator of our circadian rhythms. When bright light hits our eyes, photosensitive cells communicate with a region in the hypothalamus called the suprachiasmatic nucleus (SCN), which is thought of as the body’s “central clock.”9
The SCN regulates clock genes found in cells throughout our bodies. However, growing evidence shows that light can also regulate mood, learning and other functions without affecting circadian rhythm.10,11
12 Health Consequences of Light Pollution
Light pollution is a major problem in the developed world. At 10 p.m., our hunter–gatherer ancestors may have been settling down for the night under the moon, which emits a mere 0.1 to 0.4 lux of light.12,13
Compare that to home indoor lights at about 100 to 300 lux, or the bright lights in a store that can reach 1,000 lux.14 All night long, street lights and store lights create light pollution that prevents more than 99% of people in the U.S. and Europe from experiencing natural light.15
Light pollution messes with the body’s circadian rhythms, which can disrupt hormones and sleep. Light pollution can also affect mood and cognition without noticeable changes to the circadian rhythm. Whether indirectly or directly, these changes can cause myriad health problems.
1. Inflammation — Exposure to light at night, whether from shift work or binge-watching Netflix, increases inflammatory cytokines and decreases proper melatonin levels at night.16,17 Chronic inflammation contributes to the development of almost every chronic disease that plagues modern societies today.
2. Immune Suppression — Adequate sleep is vital for robust immune function, and facets of the immune system are under circadian control.18 Light exposure at night and disruptions in circadian rhythm both alter the body’s immune responses, making it more susceptible to infection.19,20,21
3. Hypothalamus-Pituitary-Adrenal (HPA) Axis Disruption — The HPA axis controls the stress response. When cortisol and other hormones are out of whack from too much light, circadian disruption and not enough sleep, overall cortisol levels rise and the HPA axis is impaired.22,23,24
4. Gut Problems — Because digestion is under circadian control, any disruption to this rhythm can promote the growth of inflammatory gut bacteria, decrease beneficial microbes, and upregulate intestinal permeability and lipopolysaccharide transport into the systemic circulation.25,26 This also helps explain why people who are jet-lagged experience diarrhea or constipation.
5. Thyroid Issues — Thyroid hormones have circadian rhythms, too. Sleep deprivation from ill-timed light is associated with abnormal thyroid function.27,28,29
6. Obesity — Night owls and people with sleep deprivation tend to eat more and gain more weight.30,31 Exposure to light at night, jet lag and shift work are all associated with an increased risk of obesity.32,33
7. Diabetes — Obesity itself is a risk factor for developing diabetes. Circadian misalignment and sleep deprivation have both been linked to increased insulin resistance and impaired glucose tolerance.34,35,36,37
8. Fertility and Menstrual Problems — From premenstrual syndrome to fertility, circadian disruptions can influence a woman’s reproductive health. Shift work and lack of sleep correlate with increased cortisol levels, decreased melatonin levels at night, and disrupted HPA axis, which can all wreak havoc on female fertility.38,39 Sleep disturbances may negatively influence male fertility, as well.40
9. Cardiovascular Disease — Evidence shows that disrupted circadian rhythms and sleep disorders are linked to cardiovascular disease risk.41,42 In one interesting study, “light-at-night” exposure in 700 subjects correlated with the level of progression of carotid atherosclerotic vascular disease.43
10. Depression and Mood Disorders — A clear connection between dark winter months and seasonal depression has already been demonstrated.44 Light exposure at the wrong times, in any month, can influence mood and depression risk. Poor quality sleep, which can result from abnormal light cycles and circadian disruption, is a risk factor for depression.45,46
In mice, light exposure at night altered gene expression in brain regions involved in emotional regulation, including the hippocampus.47 In a human trial, those exposed to just 5 lux of light at night had an increased risk of developing depression over 24 months of follow-up, compared to those who had less than 5 lux of light at night.48
11. Cognition and Memory Deficits — Were you ever told to get a good night’s sleep before a test? Sleep loss and jet lag are clearly associated with poor learning capacity and neurocognitive performance.49,50 Aberrant light exposure, which can lead to circadian misalignment and sleep disruption, resulted in memory and learning deficits, including reduced hippocampal neurogenesis in rodents.51,52,53
12. Cancer — Bright light at night suppresses melatonin and may increase the risk of certain cancers including breast and prostate cancer.54,55,56,57,58 Sleep deprivation, which can be caused by aberrant light exposure, is also linked to cancers.59 In fact, shift work, where workers’ sleep schedules don’t coincide with natural light cycles, is considered a probable carcinogen by the International Agency for Research on Cancer.60
Ecological Consequences of Light Pollution
The effects of light pollution extend beyond human behavior and disease. Animals and plants also have evolved along with predictable light patterns, and messing with light timing has ecological impacts. Melatonin, which is suppressed by bright light at night, directly influences the seasonal breeding of animals.61
Light pollution disrupts animal reproduction, species biodiversity, plant flowering and much, much more.62 Light pollution affects many plants and animals, including:63
How to Reduce Light Pollution at Home
You don’t have to abandon all electronic activity to mitigate the harmful effects of light pollution at home. Focus on increasing exposure to bright, natural light in the morning and reducing exposure to it in the evening. You will sleep more soundly and feel more energized when your body’s rhythms are synced up with the sun. Here are some helpful tips to get started.
Go Outside, Early
On average, people spend 93% of their time indoors or in a car — it’s no wonder our circadian rhythms are out of whack!64 Once you get out of bed in the morning, open all window shades to let in the morning light. Ideally, spend 20 to 30 minutes outside in the early morning. If that’s impossible, a 10,000 lux full-spectrum light box may suffice if you spend a good 30 minutes nearby. If you commute to work, try to drive without sunglasses to increase your light exposure.
Avoid Bright Lights Later in the Day
There are many ways to facilitate this:
- Replace LED light bulbs with incandescent bulbs. Yes, LEDs win in efficiency, but their environmental friendliness only goes so far. LEDs emit light wavelengths that are really, really good at suppressing melatonin, which you don’t want happening later in the day.
- Wear amber-colored blue light-blocking glasses in the afternoon and evening, especially if you’re using electronics. These glasses are highly effective at improving sleep and mood.65,66,67
- Install a program like f.lux that modifies a device’s display screen to be warmer in the evening and lighter during the day.
Sleep in the Dark
Darken your bedroom at night — the darker, the better. Even dim light at night can disrupt circadian rhythm.68,69 Nix the night light, install blackout curtains and remove that bright blue digital clock. Your mood, sleep and health will thank you!
How to Reduce Light Pollution at the Community Level
Light pollution negatively affects mood, sleep, ecosystems, and public health. Most of the developed world isn’t able to view the Milky Way at night. Some businesses, like hospitals, might not be able to shut down completely at night, but communities and cities can take steps to reduce light pollution.
In fact, at least 17 of the 50 United States already have laws limiting light pollution.70 Some laws require street lights to point downward, while others require low-wattage lighting at night, and even others limit the lights allowed at night. In England, almost a quarter of communities turn off street lights between midnight and 4 a.m. or 5 a.m.71 And, although it may seem counterintuitive, less light at night doesn’t seem to increase crime.72,73
For information on how to take action in your community, check out the International Dark Sky Places. This great resource provides educational materials about light pollution, and also gives tips and examples for how to talk to neighbors, communities and even legislators.