•  Artificial light — how it differs from natural sunlight and how our indoor environments, deficient in sunlight, can contribute to significant diseases, especially metabolic diseases and type 2 diabetes.

I would like to start with a quote from Dr. Martin Moore-Ede, a respected researcher in circadian rhythms. He emphasizes that for approximately 10,000 generations, the contrast between bright daylight and nocturnal darkness synchronized the human internal clock with the Earth's rotation, but in the last hundred years, this natural cycle has been disrupted by artificial light. 

Today, we spend about 90% of our time indoors, under artificial light, which is much weaker during the day than natural light and considerably stronger at night than moonlight. This shift is confirmed by a 2001 study that showed, on average, Americans spend 87% of their time indoors and another 6% in vehicles. 

Historically, humans lived under intense sunlight during the day and under night skies illuminated primarily by the moon and stars, and by firelight. Today, we live surrounded by compact fluorescent lamps and white LEDs that illuminate our environment at night, an environment that should be respected for the benefits it brings. 

The key question is: what are the implications of artificial light for obesity and diabetes?

 Let's start with an overview of natural sunlight: 

Sunlight is more than a source of light; it is a vital source of energy. Measured near sunset, sunlight shows a broad emission of visible and invisible light. The sun is a thermal light source, emitting enough energy to be perceived as "heat" even from Earth's distance. An important aspect is that sunlight has a constant emission, unlike many artificial indoor light sources. 

Throughout the day, the properties of sunlight change. As the sun rises and sets, the wavelength and color temperature change. In the morning and towards evening, visible light is accompanied by longer wavelength red and infrared light. When the sun rises in the sky, shorter wavelength photons (UVA and, eventually, UVB) penetrate the atmosphere, and in nature, blue light is always balanced by red and infrared light. 

Despite its reputation, ultraviolet light represents only a small portion of the solar spectrum. In contrast, invisible infrared light occupies a significant portion and is an essential "nutrient." Although most solar energy is in the visible spectrum, a larger percentage of photons are in the invisible infrared region. 

Why is the composition of sunlight important? 

Solar radiation, and not artificial light, has been the optimal condition for all life forms on Earth for the last 3.4 billion years. From bacteria to plants and animals, natural light has been an indispensable constant in the evolutionary process. 

Looking back at the history of artificial light: humans are believed to have domesticated fire approximately one million to 780,000 years ago. 

Before that, natural light (sun and moon) dominated. In 1879, Edison's invention of the incandescent light bulb marked a turning point, accelerating the adoption of artificial light. By 1939, the first fluorescent tube was introduced at the New York World's Fair, and in 1996, the first white LED bulb was launched. This invention was recognized with the Nobel Prize in Physics in 2007. 

Recent legislative changes in the US have practically led to a ban on incandescent bulbs, which raises significant concerns. These bulbs, known for emitting visible and invisible light, have a broad emission spectrum that includes infrared, essential for health. 

Halogen bulbs, a variant of incandescent bulbs, also emit infrared light but have been categorized as "inefficient." 

Yet, in stark contrast, modern cool white LED lighting, considered the most economical, has the narrowest and most unbalanced emission spectrum, being the most harmful to the human body. 

It is dominated by an intense blue and green peak, with red and infrared light almost absent. Compact fluorescent bulbs exhibit an even more artificial spectrum. These modern technologies also have a "flicker" effect (i.e., they flicker rapidly), which can trigger migraines and other health problems. These light sources offer only a fraction of the natural solar spectrum. 

The real problem is that most people spend 90% of their time indoors under LED bulbs (very few still use other types of bulbs), deprived of over 90% of the solar spectrum necessary for optimal physiological functioning. This disconnect is reflected in a study on melatonin supplement use: between 1999 and 2017, more and more adults started consuming melatonin for insomnia and poor sleep quality, a clear indication of the negative impact of lack of exposure to natural light. 

PMID: 35103775. 

Light interacts with the eyes and skin in different ways. Short wavelengths are superficially absorbed, while long ones, such as infrared, penetrate deep into tissues. 

A transformative idea, in both conventional and alternative medicine, is to consider the sun's wavelengths as individual nutrients. We have evolutionarily adapted to utilize these "light nutrients," and now we have abandoned them, and their absence seriously affects health. These categories include: 

• UV: for vitamin D production, proopiomelanocortin stimulation, and nitric oxide release. 

• Visible light: especially blue and green, which affect circadian signals. 

• Long wavelengths: red and near-infrared, which interact with cellular water and stimulate mitochondria. 

Circadian rhythms and the importance of red/infrared light 

Modern artificial light is essentially just an excess of visible blue and a deficiency of red/infrared – a form of light toxicity. 

Screens, often only a few centimeters from our eyes, emit blue light in the evening, disrupting the pineal gland's natural melatonin production. This disruption affects sleep initiation, depth, and cellular repair processes. 

Melanopsin: the blue light-sensitive protein 

First discovered in the African clawed frog, melanopsin helps regulate light adaptation. In humans, melanopsin is found in the retina, skin, blood vessels, fat cells, and brain regions. It sends time signals to the body. Given this sensitivity, 18 hours of daily exposure to blue light is a major source of internal clock dysregulation. 

Our internal clocks need constant synchronization with ambient light. This mechanism involves molecular feedback loops in every cell – a fundamental process in regulating biological time. 

These mechanisms are essential for metabolic health: they control insulin sensitivity, food absorption, and energy expenditure. The master clock prepares the digestive system and regulates insulin secretion by the pancreas. 

• Artificial light and diabetes 

A study shows that exposure to bright light overnight – without consuming food – increased blood glucose and insulin levels. Thus, artificial light can induce glucose intolerance. Other research shows that light affects clock genes in the brain and liver, leading to fat accumulation. 

Mechanism 

Nocturnal lighting disrupts circadian rhythms via the visual-neuroendocrine pathway: blue light activates melanopsin in ipRGCs (intrinsically photosensitive retinal ganglion cells), which signals directly to the suprachiasmatic nucleus (SCN) in the hypothalamus, the body's "central clock"—thus inhibiting melatonin and disrupting overnight hormonal cycles. 

Studies in rodents show that light exposure (just 1 hour at night) decreases pancreatic β-cell sensitivity and disrupts insulin secretion; through neuronal connections (SCN → pancreas/adrenal), light stimulates hepatic glucose production and suppresses insulin release. 

A prospective study in the UK Biobank, with ~18,700 diabetes cases over 13 years, identified that intense exposure to blue light (from screens, LEDs) is associated with an increased risk of type 2 diabetes (HR 1.17, 95% CI 1.12–1.23), even in people with intense physical activity or healthy sleep. 

PMID: 38157962. 

Another Australian study in The Lancet Regional Health – Europe, on 85,000 participants, shows that nocturnal light (between 00:30–06:00) is one of the strongest predictors of diabetes, by altering circadian rhythm and glucose metabolism, and can increase your risk of type 2 diabetes by up to 67%. 

https://doi.org/10.1016/j.lanepe.2024.100943 

What does this have to do with fatty liver? 

Exposure to light at night reduces glucose sensitivity, decreases insulin secretion, and weakens the amplitude of oscillating proteins. A large-scale study found that older adults exposed to light at night had a higher prevalence of obesity, diabetes, and hypertension—even after adjusting for age, race, sex, season, sleep, and activity. In other words, if someone sleeps with the light on or is exposed to "light pollution" in the evening, they risk developing insulin resistance, abdominal fat, resistant hypertension, and, ultimately, diabetes. 

When circadian rhythms are disrupted by nocturnal light and untimely meals, hormonal rhythms and metabolism are profoundly affected. Chronic circadian changes lead to inflammation and fibrosis of adipose tissue. 

In a mouse study, those subjected to a simulated shift work schedule developed fibrotic and insulin-resistant fatty tissue, although their diet was identical to that of the control group. This clearly shows that circadian dysfunction induces leptin resistance and links nocturnal artificial light to metabolic diseases. 

Let's discuss the importance of red and infrared light. These are now considered essential nutrients, and many of us are deficient in them. 

A remarkable study illustrated the effect of red light on blood glucose. Participants were exposed to 670 nm red light applied to their back for 15 minutes before a glucose tolerance test. Those exposed to this light had significantly lower blood glucose levels—up to 27%—while all other variables remained constant. This randomized controlled study found that red light increased carbon dioxide production, indicating enhanced mitochondrial activity that allowed glucose to be metabolized more efficiently. 

PMID: 38378043. 

One of the most important scientific articles in the last five years addresses melatonin and the optical properties of the human body. This revolutionary research has not received due attention, although its implications in understanding the relationship between light and metabolic health are profound. 

Scott Zimmerman, an optical engineer without medical training, made essential discoveries about the role of infrared light in the human body. Through optical modeling of light absorption and dispersion, Zimmerman showed that this type of light penetrates deep into the body, playing a crucial role in melatonin production—not in the pineal gland, but in the mitochondria. 

Melatonin is commonly known for its sleep-inducing effects. However, it also functions as a powerful antioxidant. Just as people consume vitamin C or superfoods for their antioxidant effects, melatonin acts as a natural shield against oxidative stress and cancer. This antioxidant has been present in prokaryotic life for over 3 billion years and is produced in mitochondria when exposed to infrared light. 

The influence of infrared light surpasses any traditional understanding in chronobiology. This light penetrates deep into the body, including through the skull, due to low optical absorption and the isotropic scattering effect. The result is the production of mitochondrial melatonin in quantities tens of times greater than that produced in the pineal gland. 

The human body evolved to use infrared light, just as it perceives blue light. These photons are distributed throughout the body, especially through the cerebrospinal fluid, which acts as a light guide around the brain and spinal cord. Thus, light can reflect off the surface of the cortex and penetrate deep into the brain. 

Zimmerman's approach, inspired by the aerospace industry, highlighted that the optical structure of the human body resembles designs intended to efficiently reflect or absorb artificial light. 

This suggests that infrared light is so vital to health that our body is designed to absorb it efficiently. 

Although these photons are not absorbed as easily as blue or UV light, they reflect repeatedly within the body until they are finally absorbed. This process promotes mitochondrial melatonin production and, possibly, water structuring in the body—a topic that requires further research. 

In the field of obstetrics and women's health, a fascinating discovery has emerged about the interaction between the fetus and infrared light. In addition to cerebrospinal fluid, amniotic fluid acts as a medium with maximum transmission in the near-infrared spectrum. It functions as a dielectric integrating sphere, ensuring uniform absorption of photons by the fetus. 

This observation highlights nature's ingenuity and the importance of infrared light. By enveloping the baby in this conducive environment, nature suggests how essential exposure to sunlight is, contrary to modern advice to totally avoid the sun. The implications for maternal and fetal health are profound. 

It is, therefore, essential for women, especially pregnant ones, to spend time in natural light. No prolonged direct exposure is needed; simply being outdoors brings benefits. 

This is because red and infrared light is directly absorbed by cytochromes in the mitochondrial electron transport chain, acting as a mitochondrial "lubricant" that enhances energy production efficiency. 

Imagine these cytochromes as the pistons of a cellular engine. Without constant exposure to red and infrared light, mitochondria function like a tractor without an oil change—slowly, inefficiently, prone to breakdowns. 

In addition, the body produces intracellular melatonin, which acts as a cooling agent during the energy process. Energy production generates reactive oxygen species (ROS), which can damage mitochondrial DNA. Such damage hinders energetic synthesis, leading to chronic diseases. 

As stated by Dr. Doug Wallace, geneticist and evolutionary biologist who pioneered the use of human mitochondrial DNA as a molecular marker in 1975: "up to 95% of chronic diseases are caused by bioenergetic deficiencies." 

When mitochondria function inefficiently, energy production fails, leading to conditions such as diabetes, neurodegenerative diseases, and cancer. The lack of efficient energy production, a kind of cellular "blackout," can eventually lead to serious diseases like diabetes and cancer, depending on the affected organ and genetic predisposition. 

Red and infrared light, often overlooked, are essential for mitochondrial health. The scientific field of photobiomodulation studies the therapeutic application of these wavelengths. While some critics view red light therapy as pseudoscience, a simple search on PubMed reveals hundreds of studies on its beneficial effects on Alzheimer's, muscle recovery, or athletic performance, and hundreds more studies show a link between blue light and depression. 

This is not pseudoscience; it is photobiology. We face two major problems: (1) blue light toxicity from artificial nighttime lighting and (2) lack of exposure to natural light, especially the full spectrum of the sun, including red and infrared light. 

It is already known that lack of sunlight leads to vitamin D deficiencies and an increased incidence of chronic diseases. However, the problem is not limited to vitamin D. Lack of solar exposure also means lack of UVA and infrared light, essential for non-vitamin D metabolic pathways. 

The recipe for "diabetic light"? Disruption of circadian rhythms by artificial blue light, lack of red and infrared light, and indoor living, disconnected from the solar spectrum, for years. This reality has been shaped and perpetuated by government decisions limiting access to healthy light sources. 

The solution is simple: brighter days and darker nights. Spend more time outdoors during the day, and avoid artificial lighting at night. Following natural circadian routines can support metabolic and cellular functions. 

Living in an area different from one's ancestral origin (e.g., someone with equatorial roots moved to Tasmania) can lead to biological imbalances. It's like trying to grow coconuts in Norway—an absurdity. The human body, like plants, responds specifically to light. 

Minimal light exposure at night is essential. Total darkness is ideal. If nocturnal activity is necessary, opt for candles or low-positioned red LEDs. Although not ideal, they are much better than bright overhead LEDs. 

The human eye is extremely sensitive to blue light due to the high concentration of melanopsin proteins. If you cannot completely avoid artificial light, use blue light filtering glasses. 

In addition, reintroducing infrared light into the home through incandescent bulbs operated at low voltage brings real benefits, as demonstrated by Professor Robert Fosbury, an astronomer. 

Decisions regarding public lighting are often made by individuals without a complete understanding of the biological effects of light. For optimal health, we must remember that we are blue light sensors and infrared light collectors. 

Increasing time spent outdoors, reintroducing biological lighting, and exploring photobiomodulation are essential steps. Health problems are not just about diet, but also about the quality and timing of light exposure. Understanding this highlights the central role of light and circadian rhythms in our biological health. 

It's time to move beyond the classic paradigm, limited to nutrition and exercise, and understand health through the lens of personal ecology: light quality, sleep, rhythm, grounding, natural temperatures, and cyclic reconnection with nature. Studies show that when patients start to see improvements in energy, sleep, mood, and body weight just by making simple changes in light exposure, they become more receptive to other changes such as diet, exercise, and quitting harmful habits. 

If stopping artificial light exposure in the evening and using natural light as a nutrient is so simple, free, and so well-studied for its effects, there is absolutely no reason not to implement it.