Sunlight, Infrared & Mitochondria: The Underestimated Healing Power of Light

Clinical anecdote — not study-grade evidence: In the MedCram talk underlying this piece, Dr. Roger Seheult opens with the case of a 15-year-old boy: weakened by leukemia treatment, he develops a severe flesh-eating fungal infection (mucormycosis) in the lung. One lung is removed; the infection jumps to the other. Prognosis: terminal. His last wish: he wants to go outside, to fresh air. His bed is wheeled outdoors — and the unthinkable happens. Inflammatory markers drop, oxygen demand falls, the boy survives. Single cases are not proof of therapy, but they raise the question: which evolutionarily built-in healing mechanisms have we unlearned in our climate-controlled, artificially lit indoor world?

Dr. Roger Seheult, board-certified in internal medicine, pulmonology, and critical care (widely known through the MedCram education channel), has built his career on that question. His observations from the COVID-19 ICU suggest: the key to robust health often isn't expensive medicine, but evolutionarily ancient stimuli — light, heat, cold, movement, plant compounds.

An evolutionary dilemma: why we need the sun, yet it burns us

It looks like a design flaw of nature: the sun is essential to our survival — yet after a short time in the blazing midday sun, a painful sunburn looms. Did millions of years of evolution fail here?

The short answer: no. It isn't our biology that's poorly adapted — it's our way of life that contradicts our evolutionary heritage. According to environmental surveys, modern humans spend roughly 92–93% of their time indoors. Our deconditioned skin is then abruptly exposed, on a summer holiday, to the most intense radiation of the year — a classic evolutionary mismatch: a Stone-Age-calibrated body in an indoor world it was never built for. Sunburn is not the failure of adaptation but the bill for having unlearned the gradual, year-round acclimatization to light.

For hundreds of thousands of years, humans were exposed to the sun daily, in measured doses, year-round. The skin built seasonal protection (tanning, a slightly thickened horny layer), the sleep-wake rhythm was firmly coupled to the sun's position, and the full light spectrum — not just the UV-B for vitamin D — was a permanent biological input. Today we replace daylight with blue-heavy LED light behind glass, which filters out precisely the red and infrared fractions that act deep in tissue — and cram the missing dose into a few hours at the height of summer. Medical experts now call this chronic light deficiency the "scurvy of the 21st century": a deficiency we don't feel acutely because it builds over decades.

So the resolution of the dilemma is not "more" or "less" sun, but regular instead of episodic — the daily, moderate dose we're built for, rather than the rare overdose that burns.

The 8 pillars of health — the NEW START framework

Seheult works with a long-established lifestyle framework from the Seventh-day Adventist health movement (popularized via Hans Diehl and the CHIP program). It's old, but empirically remarkably robust:

Two of these — Sunlight and Water — carry the biochemically most interesting mechanisms that are systematically under-supplied in modern life.

Sunlight: The engine of our mitochondria

For a long time, the primary health benefit of sunlight was thought to be vitamin D synthesis via UV-B radiation. That's not wrong, but incomplete. The solar spectrum is much broader:

That's the central surprise of recent years: roughly half of sunlight is infrared — invisible to the eye, but deeply active in tissue.

Subcellular melatonin as the cellular "coolant"

With increasing age or chronic disease, mitochondrial efficiency drops by an estimated 30–70%. The result is oxidative stress — a kind of "overheating" of the cellular engine.

Here lies the most exciting finding of recent years (Reiter et al. 2020): Near-infrared light stimulates mitochondria to produce melatonin locally inside the cell. This subcellular melatonin acts as a highly potent antioxidant right at the site of oxidative stress.

Important distinction: This is not the familiar "sleep hormone" released by the pineal gland in the evening to make you tired. Subcellular melatonin is a separate, autocrine form acting directly at the mitochondrion and unrelated to the sleep-wake cycle. Details on the classical, nightly melatonin live in Sleep science: chronotypes & melatonin myths.

Seheult reports from the COVID-19 ICU: patients with metabolic comorbidities (already "overheating" mitochondria) became severely ill. When these patients got 15–20 minutes of sunlight daily, oxygen saturation often improved measurably. Anecdotal — but mechanistically plausible.

Fact-check: penetration depth of infrared through clothing

In lectures Seheult sometimes cites that infrared light penetrates up to 8 cm into the body. Biophysically, that's optimistic:

Why the systemic effect is still real: Light doesn't need to radiate 8 cm directly into internal organs. It's enough that well-perfused skin layers are reached. There it stimulates mitochondria in blood cells and vascular endothelium — and blood circulates through the whole body. So the biochemical effects distribute systemically.

That near-infrared passes through regular clothing (depending on weave and color) is physically correct — you feel it as the pleasant deep warmth of the sun even when bundled up.

Sun beyond vitamin D: the full spectrum of effects

Vitamin D is often just a biomarker that someone was outdoors at all — not the sole effect of the sun. Light acts on our biology through several independent channels:

Sun and the psyche: the serotonin lever

When light hits skin and retina, serotonin turnover in the brain rises — the messenger closely tied to well-being and drive. That's the biochemical reason most people feel noticeably better on sunny days. Conversely, months of light deficiency (dark winters, rainy regions) can trigger seasonal affective disorder (SAD). Here light therapy is well studied: a 10,000-lux daylight lamp for 20–30 minutes in the morning is antidepressant in controlled SAD trials — and simultaneously sets the circadian rhythm. The nocturnal counterpart, the sleep hormone melatonin, is covered in detail in Sleep science: chronotypes & melatonin myths.

Fact-check — "UV through glass" against bacteria: In the heliotherapy era of tuberculosis sanatoria (before antibiotics) the sun was seen as a disinfectant, and the claim persists that UV inactivates pathogens like tetanus, typhoid, or TB "even through glass." Let's differentiate: strongly germicidal is mainly UV-C, used in technical sterilization — but ordinary window glass largely blocks UV-B and UV-C (only UV-A passes). The real benefit lies in environmental hygiene (sun disinfects surfaces, laundry, air) and in the indirect immune effect — not in sunbathing "burning out" an infection inside the body. The old sanatorium successes were real but rested on a bundle of light, fresh air, rest, and nutrition, not on a glass-UV miracle.

Evidence: Sun — risk vs. benefit

This is the most interesting question, long unilaterally communicated by dermatology. The answer isn't "more sun is always good," but: moderate, regular exposure without sunburn is net strongly health-promoting. Detail:

The risk side (real, but differentiated)

The benefit side (long under-communicated)

What newer large studies show

Three more recent works sharpen the picture — and support the benefit side:

• UK Biobank (Weller group, 2024): In the largest analysis to date (over 370,000 participants, median 12.7 years), people with the most active sun exposure had a lower mortality risk — roughly −14% all-cause (HR 0.86) and −19% cardiovascular (HR 0.81). Important context: the net effect stayed positive even though melanoma incidence can rise with more sun — the mortality balance favors moderate, regular exposure, not sunburns.
• 670 nm red light & the aging eye (Shinhmar/Jeffery, UCL 2020): Just three minutes of deep-red light in the morning reactivated mitochondria in the retina and measurably improved color-contrast perception — especially in people over 40. A striking example that the red and infrared fractions of light act independently on our cellular power plants.
• Infrared in COVID-19 (Pereira et al., Brazil 2022): In a small randomized pilot trial (n=30), hospitalized COVID patients received 15 minutes of 940 nm infrared daily via an LED vest. Hospital stay shortened by about a third (statistically significant). Given the tiny sample this is a signal, not proof — but mechanistically consistent with the mitochondrial thesis.

Synthesis — the honest 2026 position: The old dermatological "always avoid sun" doctrine is outdated. Modern data show that chronic sun deficiency is an independent mortality factor — and stronger than melanoma risk under reasonable exposure. The right middle:

• 15–20 min midday sun on a large skin area (arms + legs), skin-type-adjusted (Type I–II ~10 min, Type V–VI 30–40 min)
• Never sunburn — the one hard limit
• Sun protection for prolonged exposure (hat, shade, then sunscreen) — physical protection beats chemistry
• In winter / on deficiency supplement vitamin D (see Vitamin D3 + K2)

Fever as a weapon: hydrotherapy and the innate immune system

Beyond the adaptive immune system (antibodies after vaccination/infection), humans have an innate immune system — the rapid-response force. One of its key weapons: interferon, a protein that blocks viral replication.

Interferon production is temperature-dependent

When the body develops fever, core temperature rises from ~37°C to 38.5–39°C. Studies on lymphocytes and systematic reviews (Evans 2015, Nature Reviews Immunology) show: at these temperatures interferon production is significantly elevated — depending on subtype and study, by a factor of 3 to 10.

Consequence: Suppressing fever purely symptomatically with paracetamol or ibuprofen, without medical necessity, robs the body of its strongest antiviral response. For vulnerable groups (small children, pregnant, comorbidities) different rules apply — but for a healthy adult with moderate fever, "endure and sleep through" is often the immunobiologically better choice.

Hydrotherapy — creating the warmth artificially

The demargination effect is mechanistically clean: at rest, some white blood cells "stick" passively to vessel walls. Cold stimulus → vessels contract → these cells get flushed into the bloodstream and actively patrol again.

Phytoncides: The pharmacy of the forest

Japanese research on forest bathing (Shinrin-Yoku) has opened a further, light-spectrum-independent healing domain. Trees release phytoncides — volatile essential compounds (especially α-pinene, limonene, camphene) that protect them against insects and fungi.

What happens in humans (Li 2010, Environmental Health & Preventive Medicine):

• NK cells (natural killer cells) rise by ~50% after a 2-day forest stay
• Effect lasts up to 7 days after return
• CRP (chronic inflammation marker) measurably drops
• Cortisol daily profile normalizes

Practically: one longer forest walk per week delivers immunological effects lasting weeks. Urban green helps too, but forest > park > grey city.

Practical application: The light-warmth-nature weekly routine

Bringing the eight NEW START pillars into an actionable week:

This routine is free (except sauna membership) and better-evidenced than most expensive supplements. See What is longevity? for the overall context, and Exercise & longevity for the strength-training pillar.

Conclusion

We are at the core the scurvy patients of the 21st century — only we're not lacking vitamin C, but real sunlight, thermal stimuli, plant air, and movement in natural settings. About 90% of our lifetime, per EPA estimates, is spent indoors — isolated from precisely those stimuli for which our biology was optimized over hundreds of thousands of years.

The way back doesn't require quitting modern life — just deliberate mini-adaptations:

• 15 min of unprotected daylight on skin, daily
• Contrast showers as mini-hydrotherapy
• Screen detox in the evening, so the pineal gland can work
• One hour of forest per week
• Vitamin D in winter once the level drops
• Social + spiritual connection as a resilience reservoir

That sounds unspectacular. But: the unspectacular is precisely what makes the difference across decades in longevity research. While the pharma industry works on the next wonder molecule, the biggest lever still lies in the sun, the cold water, the forest path — and in the consistency we bring there every single day.