The Sun Is Not Your Enemy
What a Critical Care Doctor Wants You to Know About Light, Longevity, and Disease
Think about the last time you were truly outside — not just walking from a building to a car, but genuinely exposed to open sky, surrounded by green, with the sun reaching your skin. For most people living in the modern world, that experience is increasingly rare. And according to a growing body of medical science, that absence may be quietly driving some of the most prevalent and deadly diseases of our time.
Dr. Roger Seheult, a board-certified intensivist who specializes in pulmonary and critical care medicine, has spent his career at the intersection of life and death. As the physician you see when you are critically ill in an intensive care unit — the one making split-second decisions about ventilators, vasopressors, and medication interventions — he has developed a rare clarity about what actually kills people, and what can be done far earlier to prevent it. What he shares cuts against much of what mainstream health messaging has told us for decades.
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Before diving into sunlight, it helps to understand how Dr. Seheult frames human health. He uses the image of a chain — each link representing an organ system: heart, lungs, liver, kidneys, brain, and so on. Over a lifetime, those links begin to erode. At some point, one link becomes noticeably weaker than the others, and that is where disease concentrates.
Modern medicine, he explains, is largely designed to leverage the stronger links to protect the weakest one. This is why medications have side effects — because strengthening one link often comes at the expense of others. That trade-off is sometimes necessary in an emergency, but it is not a strategy for living well.
The real goal, then, is to keep all the links strong simultaneously, and to do that from as early an age as possible. This is the philosophy behind what he calls the eight pillars of health — organized into the mnemonic NEWSTART: Nutrition, Exercise, Water, Sunlight, Temperance, Air, Rest, and Trust.
The Big Lie About Sunlight
Of all eight pillars, Dr. Seheult says sunlight is where the most overlooked and most urgent science is happening right now. And it starts with correcting a pervasive misconception.
Sunlight is not one thing. It is a broad spectrum of radiation, ranging from ultraviolet B (UVB) at the short-wavelength end to infrared light at the long-wavelength end. UVB is what produces vitamin D in the skin. But vitamin D accounts for only a fraction of sunlight's effect on the human body. The far more consequential — and largely invisible — part of the spectrum is infrared radiation.
Long-wavelength red and infrared light penetrates deeply through biological tissue and has the ability to improve mitochondrial function and ATP production — with effects that extend systemically, even to tissues not directly exposed to the light. To understand why this matters so profoundly, we need to talk about the mitochondria.
The Powerhouse Problem
You may remember from school that mitochondria are the powerhouses of the cell — the organelles that produce energy. What is less commonly known is what happens to them as we age:
Imagine running your household on 30% of its normal electrical supply. Certain appliances would simply stop working. Others would function poorly and erratically. This is what happens across the body's organ systems as mitochondrial function declines. In the liver, the result is increased fat accumulation. In the heart, congestion. In the brain — dementia.
The root cause underlying a staggering number of chronic diseases is not simply aging itself, but the progressive failure of mitochondria to produce adequate cellular energy. The mechanism behind this failure is oxidative stress — a buildup of reactive oxygen species that essentially overheat the mitochondria from the inside. Like an engine without a cooling system, the mitochondria eventually become inefficient and begin to break down.
Now here is the crucial part: the mitochondria have their own built-in cooling system. And it is activated, in large part, by sunlight.
Infrared Light, Melatonin, and the Cellular Cooling System
In 2019, light engineer Scott Zimmerman and melatonin researcher Dr. Russell Reiter published a paper proposing that infrared radiation from the sun penetrates the body — up to approximately 8 centimetres — and directly interacts with mitochondria. What does it do when it gets there?
It stimulates and upregulates the production of melatonin inside the cell itself. This is not the melatonin most people are familiar with — the hormone released by the pineal gland in the brain that signals sleep onset. This is mitochondrial melatonin, produced locally within cells, functioning as a powerful antioxidant. It neutralizes oxidative stress. It keeps the cellular engine cool.
A randomized controlled trial showed that COVID-19 patients treated with 940nm infrared light recovered more quickly, being discharged four days earlier than controls — a statistically significant finding even in a study of just 30 patients.
Another study from Glen Jeffery's laboratory at University College London showed that exposing individuals to 670nm red light led to a 27% reduction in glucose spikes following meals, suggesting that mitochondrial enhancement via light exposure yields systemic metabolic benefits.
What makes this particularly striking is that the effect appears to be systemic. You do not need to expose every part of the body to achieve results. The mitochondria appear to communicate with each other — a local stimulus can produce a whole-body response.
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🔍 Search FlightsVitamin D Was a Marker, Not the Mechanism
During the COVID-19 pandemic, a consistent pattern emerged in hospital data: patients with high vitamin D levels tended to survive; patients with low vitamin D levels tended to die. Physicians began supplementing patients with vitamin D tablets in response. The supplements, however, had little measurable effect on outcomes.
Dr. Seheult's interpretation: vitamin D was a proxy — a signal of who was spending time outdoors and who was not. Supplementing the vitamin without the light was like replacing the dashboard warning light without fixing the engine.
Studies across the United States, England, and Italy showed that regions with more sunlight had lower COVID-19 mortality — and crucially, this association held independent of vitamin D levels. Something else in sunlight was doing the protective work.
The Seasonal Pattern of Death
When you map mortality rates across a calendar year — cardiac deaths, respiratory deaths, kidney deaths, infectious disease deaths — a single, clear pattern emerges: the greatest number of deaths occur within approximately one month of the shortest day of the year.
This pattern reverses in the southern hemisphere, where winter falls in June and July, and where the peak mortality window shifts accordingly. The correlation is not with temperature, not with holiday gatherings, not with humidity. It is with the length of the day — a proxy for the amount of sunlight.
What You Can Do
The practical implications are surprisingly accessible:
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Get outside for 15–20 minutes daily This is the duration at which research identifies a biological switch being activated in the mitochondria. After approximately 15–20 minutes, further stimulation provides no additional benefit. Consistency matters more than duration.
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Morning and evening are ideal times When the sun is lower on the horizon, the atmosphere filters out more UV radiation while allowing infrared light to pass through. You get the mitochondrial benefit with less UV exposure risk.
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Cloudy days still count Clouds absorb infrared light, but being outside in diffuse daylight still delivers more infrared radiation than being indoors. Do not let overcast weather become a reason to stay inside.
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Trees amplify the benefit Forests and green spaces are highly reflective of infrared light. In one remarkable study, 8,000 trees were planted in a 4-square-mile urban area — and two years later, inflammatory markers in residents had dropped by 13–20% with no other interventions.
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Your indoor lighting matters Modern LED bulbs emit a narrow blue-dominant spectrum without the infrared component that has always accompanied light in human history. Consider full-spectrum alternatives where possible.
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Artificial red light devices can help when sunlight is inaccessible Red light panels and devices emitting in the 670–940 nanometer range have demonstrated real mitochondrial benefits in controlled trials — a meaningful supplement for people in high-latitude winters or long indoor shifts.
Bright Days, Dark Nights
One of the most underappreciated aspects of light and health is not just the absence of sunlight during the day, but the presence of artificial light at night. The two problems are mirror images of each other.
Your body uses light as its primary signal for regulating the circadian rhythm — the internal clock that governs when hormones are released, when repair processes occur, when sleep is initiated. Artificial light at night — particularly from screens — suppresses pineal melatonin production and confuses the circadian system into thinking the day is still ongoing.
The result is delayed sleep onset, disrupted sleep architecture, and a cascade of downstream hormonal and metabolic effects that accumulate over time. The prescription: bright light during the day, genuine darkness at night. Blue-light-blocking glasses help, but are imperfect. The most effective intervention remains turning off screens and lights as bedtime approaches, and sleeping in genuine darkness.
The Broader Framework: NEWSTART
Sunlight, for all its importance, is one component of a larger framework. Each pillar reinforces and amplifies the others:
Exercise improves mitochondrial function and reduces stroke and depression. Water — particularly hot water through sauna — has been shown in Finnish longitudinal research to reduce cardiovascular mortality with a clear dose-response curve. Clean air, especially air enriched with phytoncides from trees and forests, enhances natural killer cell activity and immune response. Rest allows the body to repair. Adequate nutrition and temperance — avoiding toxins that damage organ systems — protect every link in the chain simultaneously.
The Scurvy of the 21st Century
There is a useful historical analogy here. Imagine being aboard a sailing vessel 300 years ago and watching shipmates die of scurvy — while someone approaches and says that simply eating a small yellow fruit a few times a week would prevent it entirely. It would seem almost incredible.
That is where we are now with sunlight. The intervention is free, available to most people, requires only 15 minutes a day, and addresses the mitochondrial root of some of the most expensive and prevalent chronic diseases in the world. It has no meaningful side effects when practiced sensibly.
And yet modern humans now spend approximately 93% of their time indoors — a figure consistent across industrialized nations. We have built climate-controlled shelters, designed windows to block infrared light, outlawed full-spectrum bulbs in favor of energy-efficient alternatives, and created entertainment systems powerful enough to keep entire families sedated indoors indefinitely.
And then we wonder why rates of dementia, diabetes, cardiovascular disease, and depression continue to climb. The answer, at least in part, may be simpler than we have allowed ourselves to believe: go outside.
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