Light Pollution's Impact: Human Health At Risk

Light pollution, caused by the excessive or inappropriate use of outdoor artificial light, is detrimental to human health. The artificial light from sources such as streetlights, cars, offices, and buildings, affects the natural body rhythms of humans, disrupting the production of melatonin, a hormone that induces sleep and boosts the immune system. Research suggests that light pollution increases the risk of obesity, depression, sleep disorders, diabetes, breast cancer, and more. The American Medical Association has expressed concern about the exposure to blue light from outdoor lighting, recommending shielding light fixtures and using lower-temperature lights.

Circadian rhythm disruption

Circadian rhythm, or the sleep-wake cycle, is a biological clock that is governed by the natural day/night cycle. This cycle is largely influenced by photoreceptors in the eye that are more sensitive to blue wavelengths of light. Circadian rhythm is essential for dictating critical information on daily and seasonal behaviour patterns such as hibernation, eating, and breeding.

The amount of light entering the eye is key in helping our brain distinguish times for wakefulness and times for sleep. The suprachiasmatic nucleus (SCN) is the part of our hypothalamus that is responsible for sending time-based signals to regulate the body. The SCN is highly sensitive to light exposure, as light provides an external cue for internal clock regulation.

Exposure to artificial light disrupts our internal clock regulation. Upon light exposure, the SCN starts a signalling pathway that leads to a reduction in melatonin, the hormone responsible for regulating our sleep-wake cycle. Melatonin reduction results in daytime sleepiness and sleep disturbances. It may also modify our immunity and stress response. The amount of downregulation is dependent on the intensity and wavelength of light entering the eye. However, new research has found that even low light intensities from urban skyglow can cause melatonin downregulation.

Increased artificial light exposure has been linked to circadian rhythm sleep-wake disorders, where the circadian rhythm is misaligned with the natural light-dark cycle. Lack of melatonin and the disruption of healthy sleeping patterns are increasingly being linked to malignant cancers. Sleep pattern disruption is thought to interfere with cancer suppression genes, leading to an increased risk of breast, prostate, gastric, and lung cancers.

The impact of indoor light pollution is also significant. We now have more devices than ever that emit various types of light. Our smartphones and laptops stream out blue light, while our indoor lamps and overhead lights flood our spaces with white light. There is increasing evidence that indoor light exposure, particularly at night, can contribute to circadian rhythm disorders that have long-term health impacts. Rats exposed to continuous lighting were found to have reduced skeletal muscle function and bone deterioration. Indoor lighting disrupts the SCN's pathways in the same way as outdoor lighting.

Sleep deprivation

Light pollution can have a significant impact on human health, particularly when it comes to sleep deprivation. As artificial light disrupts our natural circadian rhythms, it can lead to various adverse effects on our health and well-being.

Circadian Rhythm Disruption

The human body follows a 24-hour circadian rhythm, also known as the sleep-wake cycle, which is influenced by the natural light/dark cycle of day and night. This cycle is governed by our biological clock, with light acting as an external cue for our internal clock regulation. However, with the proliferation of artificial light at night, this natural cycle is being disrupted.

The hypothalamus, specifically the suprachiasmatic nucleus (SCN), is highly sensitive to light exposure and plays a crucial role in regulating our sleep-wake cycles. Upon exposure to artificial light, the SCN initiates a signaling pathway that leads to a reduction in melatonin production. Melatonin is a hormone responsible for regulating our sleep, and its reduction results in daytime sleepiness and sleep disturbances.

Impact on Sleep

Research has shown a strong correlation between light pollution and sleep deprivation. A study published in the Journal of Clinical Sleep Medicine found that older adults exposed to high levels of artificial light at night experienced more sleepless nights and relied more on sleep medication. They also tended to take these drugs for longer and in higher doses than those not exposed to nighttime light.

Health Risks

Additionally, sleep pattern disruption is thought to interfere with cancer-suppressing genes, leading to a higher risk of breast, prostate, gastric, and lung cancers. The reduction in melatonin levels due to artificial light exposure at night may also play a role in the development of these cancers.

Minimizing Light Pollution

To mitigate the negative impacts of light pollution on sleep and overall health, it is essential to minimize our exposure to artificial light, especially at night. This can be achieved by using warm-colored bulbs or LED lights, turning off unnecessary indoor and outdoor lighting, and protecting our eyes from blue light with specialized glasses or screen protectors.

By taking these steps, we can not only improve the quality of our sleep but also reduce the risk of developing various health issues associated with light pollution and sleep deprivation.

Blue light and screen time

Blue light is part of the visible light spectrum and has the shortest wavelength and highest energy. Sunlight is the biggest source of blue light, but artificial sources include fluorescent light, LED TVs, computer monitors, smartphones, and tablet screens.

Blue light has several health benefits. It boosts alertness, helps memory and brain function, elevates mood, and regulates the body's natural sleep-wake cycle (circadian rhythm). Sunlight is also important for the growth and development of children's eyes and vision.

However, there are concerns about the long-term effects of blue light exposure from digital devices, particularly when it comes to excessive screen time and viewing screens up close. Blue light exposure from screens is small compared to sun exposure, but our eyes are not good at blocking it, and constant exposure over time could damage retinal cells and cause vision problems such as age-related macular degeneration. It can also contribute to cataracts, eye cancer, and growths on the clear covering over the white part of the eye. According to a study by the National Eye Institute, children are more at risk than adults because their eyes absorb more blue light from digital devices.

Blue light exposure before bedtime can also disrupt sleep patterns by suppressing the production of melatonin, a hormone that influences the circadian rhythm. Interruption of the circadian system has been linked to the development of type 2 diabetes, heart disease, cancer, sleep disorders, and cognitive dysfunctions.

To reduce the negative effects of blue light, measures such as blue-light filters for devices, following the 20-20-20 rule for eye breaks, controlling lighting and glare, and using blue light-blocking glasses can be implemented.

Melatonin deficiency

Melatonin is a hormone that is naturally produced by the body in response to darkness. It is involved in many of our body functions, including regulating the daily cycles of our systemic activities.

Light pollution can suppress melatonin production in humans and animals. Artificial light at night can, therefore, disrupt the body's natural melatonin rhythm, which has a range of negative health consequences.

The sensitivity threshold for humans is 6 lux, while street lighting is typically higher. The illuminance levels at night on a starry night are 0.001 lux, and on a full-moon night, it reaches a maximum of 0.3 lux. The skyglow of a city, a form of light pollution, can reach illuminance levels of up to 0.1 lux, and outdoor lighting can be on the order of 150 lux.

The impact of light pollution on melatonin production has been linked to several health problems, including an increased risk of certain cancers, such as breast cancer. Studies have found a positive correlation between night illumination levels and breast cancer incidence, with women living in brightly lit areas at night having a 73% higher risk of developing breast cancer than those in darker areas.

Light pollution can also impact mental health, with disrupted melatonin production linked to an increased risk of depression and other mood disorders. Additionally, it can contribute to sleep disorders, as melatonin plays a crucial role in regulating sleep-wake cycles.

Furthermore, melatonin has antioxidant properties, boosts the immune system, lowers cholesterol, and helps the functioning of the thyroid, pancreas, ovaries, testes, and adrenal glands.

Not all artificial light has the same impact on melatonin production. Blue light, which is emitted by many LEDs and electronic devices, has been found to have a more significant effect on suppressing melatonin than light with longer wavelengths.

To mitigate the negative effects of light pollution on melatonin production, it is recommended to reduce exposure to blue light at night, use dimmers and lower-CCT light bulbs, and utilize color temperature apps that adapt electronic screen colors to the time of day.

Obesity and diabetes

Light pollution has been linked to a range of adverse health effects, including obesity and diabetes.

Circadian Rhythm and Melatonin

Light pollution disrupts the natural day/night cycle, which humans have evolved to rely on. This disruption can affect the production of melatonin, a hormone that is needed to keep us healthy. Melatonin has antioxidant properties, induces sleep, boosts the immune system, lowers cholesterol, and supports the functioning of the thyroid, pancreas, ovaries, testes, and adrenal glands.

The disruption of the natural day/night cycle can also lead to weight gain and obesity. This, in turn, can increase the risk of developing diabetes.

A study of nearly 100,000 Chinese adults found that people who lived in areas with high light pollution at night were about 28% more likely to develop diabetes than those in the least polluted areas. The authors of the study estimated that more than 9 million cases of diabetes in Chinese adults aged 18 and older may be due to outdoor light pollution at night.

Another study found that people who worked night shifts had an elevated risk of developing diabetes. This was particularly true for those who had worked night shifts for 30 or more years.

Preventative Measures

To reduce exposure to light pollution, it is recommended to use light-blocking window shades, sleep masks, and bulbs that emit reddish light. Blue light, in particular, should be avoided as it is the most stimulating type of light. It is also beneficial to get exposure to daylight during the day.

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