Light Therapy Benefits: Dr. Roger Seheult on Sun Exposure

Feb 25, 2025

Sunlight Benefits for Mitochondria and Melatonin

Sunlight’s impact on human health extends far beyond its visible effects through our eyes. While morning light exposure remains crucial for circadian rhythm regulation and mood, emerging research reveals a deeper story about how light interacts with our biology. Only 38% of the sun’s energy falls within the visible spectrum. A substantial 52% exists in the infrared range, with the remainder in ultraviolet. We’re familiar with UV-B’s role in vitamin D production, but the infrared portion of sunlight holds equally fascinating properties. A groundbreaking 2019 paper in Melatonin Research by Zimmerman and Ryder demonstrated that infrared light can penetrate deep into human tissue, up to 8 centimeters through scattering. Think of it like low-frequency bass sounds that easily pass through car walls – the longer wavelengths of infrared light allow for deeper tissue penetration. Fosbury’s infrared photography experiments at the European Space Agency provide striking visual evidence of this penetration. When photographing a hand under infrared light, the entire hand illuminates without showing bones, suggesting the light either penetrates through or navigates around dense tissue. This penetrative ability becomes particularly significant when considering mitochondrial function. These cellular powerhouses don’t just produce energy – they generate melatonin in concentrations orders of magnitude higher than the pineal gland. This local melatonin production plays a crucial role in managing oxidative stress, which is fundamental to cellular health. The implications are profound when we consider that mitochondrial dysfunction underlies many chronic diseases, including diabetes, hypertension, heart disease, and dementia. After age 40, mitochondrial ATP production typically drops by 70% – imagine your house operating on 30% of its normal power supply.

PREMIUM CREATINE

Momentous Creatine

Boost muscle performance & cognitive function with ultra-pure Creapure® creatine monohydrate.

Pure Creapure® from Germany

Supports Muscle Strength & Power

Enhances Cognitive Function

90 Servings | Zero Fillers

SHOP MOMENTOUS CREATINE →

Understanding sunlight’s interaction with our biology beyond just its effects through our eyes opens new perspectives on health optimization. The infrared component of sunlight may be a key player in maintaining mitochondrial function and, by extension, overall cellular health. You can experience this penetrative power yourself: On a sunny day, wear multiple layers of clothing and try to sense the sun’s position with your eyes closed. The warmth you feel is infrared radiation penetrating your clothes and skin, reaching deep into your tissues.

Melatonin Production and Cellular Function

The dual nature of melatonin in our bodies presents a fascinating paradigm that extends far beyond its commonly known role in sleep regulation. While most are familiar with melatonin as the hormone of darkness secreted by the pineal gland, its cellular function reveals a more complex and vital mechanism. Within our cells, particularly in the mitochondria, melatonin serves as one of the body’s most powerful antioxidants. Unlike its pineal counterpart, this cellular melatonin isn’t secreted into the bloodstream but operates locally, protecting against oxidative stress caused by reactive oxygen species (ROS). Seheult explains that mitochondria require a constant “cooling system” to manage oxidative stress, much like a car needs a cooling system for heat. During daylight hours, this system is powered by sunlight, particularly through long-wavelength light including red and near-infrared frequencies. These wavelengths penetrate clothing and skin, triggering melatonin production within cellular mitochondria at levels up to 20 times higher than what’s found in blood. The process involves the mitochondrial electron transport chain, where fuels like carbohydrates, proteins, and fats are burned to produce energy. This creates highly charged electrons that must be carefully managed. Oxygen serves as the final electron acceptor in this chain, but the process can generate harmful free radicals that need neutralization. At night, the system shifts. The pineal gland releases melatonin into the bloodstream, which diffuses into cells and mitochondria, maintaining antioxidant protection during darkness. Huberman notes this might explain why sleep is so restorative, as it coincides with elevated melatonin levels and reduced core body temperature. While modern technology offers various red light devices, the sun remains the premier source of these beneficial wavelengths. Even on cloudy days, some of this light penetrates the atmosphere, though cloud cover does reduce infrared transmission due to water vapor absorption. The message is clear: natural sunlight exposure, particularly during daylight hours, plays a crucial role in cellular health through this melatonin-mediated mechanism.

Green Spaces and Red Light Benefits

The profound impact of natural infrared light on human health extends far beyond what most people realize. When we explore the cellular mechanisms, particularly within our mitochondria, we discover something remarkable: infrared radiation stimulates melatonin production within cells, creating a cascade of beneficial effects. What makes this particularly fascinating is how nature has optimized this process. Chlorophyll-containing plants – trees, grass, and other green vegetation – act as powerful reflectors of infrared light. When you’re surrounded by green spaces, you’re not just getting direct infrared exposure from the sun; you’re receiving two to four times more infrared light through reflection from the surrounding vegetation. This reflection phenomenon explains why standing under a tree on a hot summer day feels significantly cooler than standing in direct sunlight. While sun-exposed objects become scorching hot, leaves remain cool because they’re reflecting rather than absorbing infrared radiation. The health implications are substantial. Research has consistently shown that people living in green spaces experience reduced rates of diabetes, hypertension, and overall mortality. But correlation doesn’t always equal causation, and scientists have worked to isolate the specific benefits of green spaces from other lifestyle factors. A groundbreaking study in Louisville, Kentucky, provided compelling evidence. Researchers measured inflammation levels (using hsCRP as a marker) in residents across a four-square-mile area. They then planted over 8,000 mature trees throughout the region. After 2-3 years, with no other demographic or lifestyle changes in the population, they found a 13% reduction in inflammation levels – comparable to the benefits of exercising three times per week. This inflammation reduction is particularly significant because elevated CRP levels are associated with numerous serious conditions, including eye diseases, heart attacks, and various inflammatory disorders. The study demonstrates that simply increasing green space in an urban environment can have measurable physiological benefits for residents. The mechanism appears to be linked to the interaction between infrared light and cellular function. When red and near-infrared light penetrates deeply into our tissues, it enhances mitochondrial efficiency through multiple pathways, including effects on cytochrome c oxidase and nitric oxide production. This becomes increasingly important as we age, potentially offering a natural countermeasure to the mitochondrial decline that characterizes cellular aging.

Red Light Benefits for Vision and Metabolism

The power of red light and sunlight exposure on human health extends far beyond what most people realize. Recent scientific evidence reveals profound effects on vision, metabolism, and overall mortality. Research from University College London demonstrates that just three minutes of morning exposure to 670-nanometer red light can improve color sensitivity by 17% in older adults, with benefits lasting for days. This effect likely stems from the retina’s uniquely high concentration of mitochondria – our cellular powerhouses – which require immense energy to process visual information rapidly. Jeffrey’s subsequent research showed even more striking results. In a controlled study, subjects exposed to red light while consuming glucose displayed lower blood sugar peaks and higher carbon dioxide exhalation, indicating enhanced metabolrial function and energy utilization. But the benefits of light exposure extend beyond controlled laboratory settings. A large-scale study by Oxford and the University of Leyden examined 10,000 subjects, revealing that increased sunlight exposure over just seven days predicted improved insulin sensitivity and reduced triglycerides. Perhaps most compelling is the Swedish study of 30,000 women tracked over 20 years. Those with high sun exposure showed significantly lower all-cause mortality, cardiovascular mortality, and even cancer mortality compared to sun-avoiders. The magnitude of this effect was so substantial that sun-seeking smokers had similar mortality rates to sun-avoiding non-smokers. These findings were later replicated in a massive UK Biobank study of 400,000 people, which used UVA radiation as a proxy for overall sunlight exposure. The results were consistent across both genders, prompting even dermatologists to reconsider their traditionally cautious stance on sun exposure. Seheult suggests these findings point to a broader epidemic of mitochondrial dysfunction, potentially underlying many modern health conditions including diabetes, hypertension, and dementia. The solution may be surprisingly simple: strategic exposure to specific wavelengths of light, particularly red light and natural sunlight. We’re witnessing a paradigm shift in our understanding of light’s role in human health. While previous generations focused primarily on light’s harmful effects, emerging research suggests judicious exposure to both natural sunlight and specific wavelengths like red light may be crucial for optimal metabolic function and longevity.

Sunlight Exposure Benefits and Cancer Risks

Recent scientific evidence challenges our traditional understanding of sunlight exposure and cancer risk. According to derma oncologist Solimani, while excessive UV exposure can accelerate skin aging and increase the likelihood of certain skin cancers, there is no evidence linking sunlight exposure to deadly melanomas. These aggressive skin cancers appear to be more influenced by genetic factors than environmental ones. This revelation aligns with mounting research demonstrating the broad health benefits of regular sunlight exposure. The key lies in intelligent exposure management rather than complete avoidance. Modern technology has made this easier than ever, with numerous free applications available to track UV index throughout the day. These tools allow us to optimize our sun exposure while minimizing risk. For those concerned about UV damage, clothing provides an effective barrier. A single layer of fabric offers substantial UV protection while still allowing beneficial infrared light to penetrate. Seheult suggests that fair-skinned individuals can wear protective clothing like broad-rimmed hats and long-sleeve shirts while still benefiting from outdoor exposure, particularly in green spaces. The interaction between infrared light and natural environments, especially areas with abundant vegetation, appears to offer additional health benefits. Research from Louisville, Kentucky has demonstrated measurable positive outcomes simply from increasing tree coverage in urban areas. This nuanced approach to sun exposure represents a shift from the oversimplified “avoid sun at all costs” message that has dominated public health discourse. Instead, we should focus on intelligent exposure: seeking regular sunlight while using appropriate protective measures during peak UV hours. The evidence suggests that complete sun avoidance may be causing more harm than good. By understanding the different components of sunlight – UV, visible, and infrared – we can make more informed decisions about our sun exposure, potentially improving our overall health while still protecting against skin damage.

Sunlight Impact on Flu Season and Latitude

The relationship between sunlight exposure and viral infections, particularly influenza, reveals a fascinating pattern that has been extensively studied. Harvard Kennedy School’s research during the 2009 H1N1 pandemic provided crucial insights, as Seheult explains. This unique pandemic peaked during summer, effectively decoupling the virus from traditional winter-associated variables like indoor gatherings, temperature, and humidity. By analyzing solar radiation data across different locations, researchers conclusively determined that sunlight serves as a powerful protective factor against influenza. This finding gains further support from a 2021 COVID-19 study examining the autumn surge in Europe. While temperature and humidity showed no correlation with infection rates, latitude emerged as a perfect predictor of surge timing. The pattern began in Finland and systematically moved southward, reaching Greece last, directly mapping the reduction in daylight hours as winter approached. This latitude effect manifests globally in influenza patterns. The United States experiences peak influenza mortality one to three weeks after the winter solstice, while Australia sees its peak in late June to early July. Singapore, situated near the equator, displays random influenza peaks without seasonal patterns. Historically, medical practitioners understood the healing power of sunlight. Hospitals commonly featured sun decks where patients would be placed for recovery. This practice, though seemingly old-fashioned, aligns with modern scientific understanding of sunlight’s protective effects against viral infections. These findings suggest that our ancestors’ intuitive understanding of sunlight’s therapeutic properties was well-founded. Modern research has simply provided the data to support what medical practitioners observed over a century ago. The correlation between latitude, sunlight exposure, and viral infection rates offers compelling evidence for the role of natural light in human health and immune function.

Sunlight Requirements and Exposure Times

The modern shift away from sunlight exposure represents a classic case of scientific reductionism gone awry. While research has demonstrated that ultraviolet light can cause cancer, this narrow focus ignores a crucial detail: throughout human evolution, UV exposure has always been packaged with infrared light. Nature, in its wisdom, never delivers blue or ultraviolet light without the presence of infrared light—except when it comes from artificial sources. Recent studies have revealed a remarkable insight: just 15 minutes of daily sunlight exposure can produce significant physiological benefits. Research conducted in Brazil demonstrated that this modest amount of daily exposure helped COVID patients leave the hospital faster. The effectiveness appears consistent across various species, from humans to bees and insects, suggesting a fundamental biological mechanism at work. The sun delivers approximately 100 milliwatts per square centimeter of light energy by the time it reaches Earth’s surface, with infrared light accounting for about 20 milliwatts. Seheult notes that after 15-20 minutes of exposure, there are diminishing returns on the benefits. This natural dosage proves far more potent than artificial alternatives, which typically deliver just 2.9 milliwatts per square centimeter. Timing of exposure shows flexibility—the benefits appear consistent regardless of when you receive sunlight during daylight hours. However, those with skin sensitivity should exercise caution during peak UV hours when the sun is highest. The challenge intensifies during winter months when natural light becomes scarce. Modern lifestyle patterns have created an unprecedented disconnect from natural light. EPA data reveals that Americans spend 93% of their time indoors—86% inside buildings and 6-7% in vehicles. This represents a dramatic shift from previous generations when outdoor activity was routine, especially for children. The solution needs to be practical within our modern constraints. Taking a lunch break outside, even if it’s during peak UV hours, provides a viable opportunity for necessary light exposure. While not ideal, some exposure during high-UV periods proves better than none at all, particularly for those constrained by typical work schedules. The winter months present a particular challenge. Many people find themselves caught in a light-deprived cycle: leaving for work before sunrise, spending daylight hours indoors, and returning home after sunset. This pattern may contribute to seasonal health challenges, including the winter influenza surge.

Light Therapy Benefits in Winter vs Summer

Sunlight exposure isn’t just about vitamin D or mood enhancement—it’s a fundamental aspect of human health that we’ve increasingly divorced ourselves from in modern life. The evidence is compelling: our relationship with natural light plays a crucial role in metabolic health, disease prevention, and overall well-being. Recent research on infrared light therapy reveals a fascinating pattern. When subjects were exposed to infrared lamps (850nm wavelength) for four hours daily over eight weeks, the results showed a marked difference between summer and winter applications. The therapy proved ineffective during summer months, likely due to adequate natural sunlight exposure. However, winter applications demonstrated statistically significant benefits. This seasonal pattern extends beyond controlled studies. Examining mortality rates across the United States reveals a striking correlation: deaths from various causes—including cardiac disease, kidney disease, and Alzheimer’s—peak approximately one to three weeks after the winter solstice and reach their lowest point shortly after the summer solstice. It’s crucial to note that when implementing light therapy, more isn’t necessarily better. The body exhibits what’s known as a biphasic response to infrared light—excessive exposure can be detrimental rather than beneficial. The key is to match artificial light exposure to natural sunlight levels. Consider this sobering statistic: we spend 93% of our time indoors, sheltered from the infrared light our bodies evolved to require. Modern LED lighting, while efficient, filters out these beneficial wavelengths. This widespread light deprivation may be more significant than we realize—Seheult estimates that proper sunlight exposure alone could potentially reduce obesity-related metrics by up to 30%, independent of dietary changes or exercise. The solution may be simpler than we think. Rather than pursuing complex interventions, the most accessible health improvement might be right outside our window. Just 15 minutes of daily sunlight exposure, particularly during winter months, could yield substantial metabolic benefits. This isn’t just about getting vitamin D—it’s about engaging with a fundamental biological need that modern life has obscured. The implications are particularly relevant for those living in northern regions like Boston, New York, England, or Sweden, where natural sunlight is limited. For these populations, strategic light therapy during winter months could serve as a vital tool for maintaining metabolic health and preventing chronic disease.

Benefits of Natural Light and Sun Exposure

Light is not just about illumination—it’s about survival. The relationship between humans and sunlight is as old as our species, yet modern life has disrupted this vital connection in ways we’re only beginning to understand. Research shows that our ancestors’ wisdom about sunlight wasn’t merely folklore. In the early 1900s, scientists won a Nobel Prize for using phototherapy to treat lupus. During the tuberculosis era, sanitariums were strategically built at high altitudes to maximize patients’ exposure to ultraviolet light. Florence Nightingale, the founder of modern nursing, observed that fresh air and direct sunlight were the two most powerful factors in soldier recovery during the Crimean War. But here’s what most people get wrong about sunlight: they assume that if it’s not a perfectly clear day, there’s no benefit to being outside. This couldn’t be further from the truth. Even on overcast days, the number of photons reaching Earth’s surface is exponentially higher than at night. Unless you’re living in a cave, you have access to beneficial light year-round. A recent study examining light exposure patterns revealed a concerning trend: “dark days and bright nights.” While we understand the dangers of artificial light exposure at night, we’re only beginning to grasp the severe health implications of insufficient daytime light exposure. The data showed that mortality rates were significantly affected by light exposure timing—with early morning light exposure providing substantial benefits. The modern hospital system, despite its technological advances, has largely abandoned the therapeutic use of natural light. Seheult shares a remarkable case of a 15-year-old leukemia patient with a severe fungal infection. After being moved outside for five hours daily—against all medical expectations—the patient’s condition dramatically improved. While this is an anecdotal case, it echoes what controlled studies have consistently shown about the therapeutic potential of natural light. The challenge isn’t understanding the benefits of sunlight—we have ample evidence for that. The real challenge is restructuring our modern lives to incorporate more natural light exposure. This isn’t about following the latest biohacking trend; it’s about reclaiming a fundamental aspect of human health that we’ve neglected. Start by tracking your outdoor time for one week. Be honest about how much time you spend outside without sunglasses. Most people are shocked to discover they barely see natural light at all. Your health is literally in the dark. The solution doesn’t require elaborate equipment or expensive treatments. It simply requires a commitment to step outside, especially in the morning hours. Even on cloudy days. Even when it’s cold. Even when it’s raining. Because the alternative—continuing our current pattern of light deprivation—is far more costly to our health than we realize.

Light Therapy Benefits in Hospitals and at Home

Light therapy is one of the most underutilized yet powerful tools in modern healthcare. The evidence supporting its effectiveness is overwhelming, yet many institutions continue to overlook its potential. Consider this: patients in hospital rooms with windows discharge faster than those without. This isn’t merely correlation – controlled studies have demonstrated that targeted light exposure can reduce hospital stays by up to four days. When you consider the astronomical costs of hospitalization, this simple intervention becomes even more remarkable. Huberman describes a personal protocol that combines 10,000 lux white light with red and near-infrared light exposure. While this setup attempts to simulate natural sunlight, it’s important to note that there’s no true replacement for actual sun exposure. The key is getting natural light in your eyes daily, regardless of weather conditions. The implications for healthcare facilities are significant. A study from Brazil demonstrated that just 15 minutes of daily light therapy through an LED jacket improved oxygen saturation, breathing capacity, heart rate, respiratory rate, and even lymphocyte counts in patients. The control group stayed in the hospital for approximately 12 days, while the intervention group was discharged after only 8 days. Seheult suggests that incorporating structured sunlight exposure into hospital protocols could be transformative. He envisions dedicated outdoor units where patients receive 20-30 minutes of supervised sun exposure – similar to how patients are routinely transported for other medical procedures. The phenomenon of ICU psychosis further underscores the importance of proper light exposure. Previously healthy individuals can develop temporary psychosis due to disrupted circadian rhythms caused by constant artificial lighting and sleep interruptions. This condition typically resolves once patients return home and resume normal light-dark cycles. For healthy individuals, the prescription is simple: 15 minutes of daily sunlight exposure. If natural sunlight isn’t accessible, consider artificial light alternatives. However, the key message remains clear – proper light exposure isn’t just about comfort or well-being; it’s a fundamental aspect of human health that our medical institutions need to take more seriously. The data supporting light therapy’s benefits continues to mount, yet implementation lags behind. As Huberman notes, we’re sitting under an avalanche of evidence telling us exactly what we need to do. The question isn’t whether light therapy works – it’s why we aren’t using it more extensively in our healthcare systems.

Sleep Darkness and Light Exposure at Night

The impact of darkness on sleep quality cannot be overstated. Research published in the Proceedings of the National Academy of Sciences revealed that even dim light exposure during sleep significantly affects morning blood glucose levels. The study compared children sleeping in completely dark rooms versus those with a mere 100 lux light source—equivalent to a night light. What’s particularly striking is the extraordinary sensitivity of our visual system to light at night. Huberman emphasizes that according to research from Harvard Medical School, just 15 seconds of artificial light exposure can significantly suppress melatonin production. Even more remarkable, the human eye’s rod cells can detect a single photon of light, and these signals can disrupt our circadian rhythm. For those living in environments with excessive light pollution, practical solutions exist. Seheult recommends using aluminum foil on windows for complete darkness, especially beneficial for night shift workers. Eye masks, particularly those made of silk or faux silk, provide an effective barrier. However, simply closing your eyes isn’t sufficient—photons can penetrate the eyelids, potentially disrupting melatonin production. When navigating at night, using a flashlight pointed away from your eyes is acceptable. The key distinction lies in direct versus indirect light exposure. While looking at a dimmed phone screen can be detrimental, using it as a flashlight to illuminate your path poses minimal risk to your circadian rhythm. Alternative solutions include using red light sources or switching your phone to red light mode. The relationship between light exposure and metabolic health is profound. Seheult references the case of the head of chronobiology at the National Institutes of Mental Health, who lost 80 pounds by optimizing his light exposure patterns and sleep schedule. This transformation occurred simply by aligning his daily rhythms with natural light cycles, despite living in Baltimore’s challenging climate. Timing of food intake also plays a crucial role. The evidence suggests we should limit eating to daylight hours, with dinner ideally consumed around 6:00-6:30 PM. Sleep quality improves significantly when you haven’t eaten for several hours before bed, though extreme hunger can also disrupt sleep. Remember that while these physiological principles are important, they shouldn’t become sources of anxiety. As Seheult notes, the goal is to implement these practices consistently while maintaining flexibility. We’re human, after all, and perfection isn’t the objective—progress is.

Modern Indoor Life vs Natural Light Patterns

Modern life has created a peculiar paradox: we’re constantly trying to bring the outdoors inside. We exercise in gyms instead of doing physical labor outdoors. We supplement sunlight with artificial lighting. We spend most of our time within four walls, disconnected from the natural environment that shaped our biology for millennia. The reductionist approach to science, while valuable, often misses the complex interplay of natural elements. Seheult points to a stark example: researchers once noticed that lung cancer patients with diets rich in vitamins E and A showed better outcomes. When they attempted to replicate these benefits through isolated, high-dose supplementation, the results were so poor they had to stop the study early. Our relationship with light epitomizes this disconnect. Throughout human evolution, we experienced blue light alongside red light and the full biological spectrum. Today’s LED lights, while energy-efficient, emit a narrow range of visible light, often lacking red light entirely. Commercial fluorescent lighting in stores and offices is severely tilted toward short wavelengths. Consider this: a bright candle or roaring fireplace only emits between 1-10 lux of light. Yet, a small LED from a hotel thermostat can emit 100-400 lux. These seemingly dim artificial lights disrupt our glucose regulation, as demonstrated in peer-reviewed studies. The positioning of light matters too. Our photoreceptors are located in the lower portion of our retina, making overhead lighting particularly disruptive to our circadian rhythms. The Scandinavians understood this intuitively, preferring table-level lighting in the evening rather than ceiling lights. Modern architecture compounds these issues. Low-E glass windows, designed for energy efficiency, filter out infrared light. Combined with LED bulbs replacing incandescent lighting, we’ve created indoor environments that are fundamentally at odds with our biological needs. The aquarium hobby offers surprising insights into the importance of proper lighting. Expert aquarists understand that fish and plants cannot thrive under pure blue light – they require full-spectrum lighting that mimics natural conditions. Yet humans continue to subject themselves to unnatural lighting patterns that would be considered harmful in any serious aquarium setup. Our current lifestyle inverts natural light patterns: dim days indoors followed by bright, short-wavelength light exposure at night. This disruption likely plays a major role in our metabolic health crisis, potentially ranking among the top two factors alongside diet and exercise. The solution isn’t about building expensive atriums or spending all day outside. Instead, it’s about taking small steps toward brighter days and darker nights. We need to reassess our relationship with artificial light and recognize its impact on our cellular function. As Huberman suggests, proper mitochondrial function – and by extension, our overall health – is downstream of our relationship with light.

Read Andrew Huberman

Discussion about this post