Overview
Indoor sedentary lifestyles have left most people seriously deficient in sunlight. The full spectrum does several distinct things at once: ultraviolet on the skin produces vitamin D from cholesterol, visible and red light penetrates through the body and reactivates the cytochrome oxidase enzyme that powers mitochondria, and bright light through the eyes drives the production of pregnenolone, progesterone, and testosterone. Darkness is itself a stressor: cortisol begins rising within fifteen minutes of the lights going off, and mitochondrial enzymes start failing after twelve to fifteen hours of darkness. The single real concern with the sun is sunburn, and sunburn is largely a polyunsaturated-fat-amplified response. People who keep their PUFA load down, their saturated fats up, and their vitamin D in the protective range can spend hours in intense sun without burning. The sun phobia and sunscreen culture has driven up rates of rickets and vitamin D deficiency conditions, and many sunscreens are directly carcinogenic in skin contact.
Key Points
-
Sunlight drives the production of progesterone, testosterone, and pregnenolone through the eyes. Long days raise these defensive steroids and short days lower them. Birds in Times Square mate year-round under the bright lights, animals with delayed implantation become pregnant around March 21st when daylight crosses the night length, and humans respond to the same signal.
-
Red light penetrates the body and restores the cytochrome oxidase enzyme that powers mitochondria. Twelve to fifteen hours of darkness damages this enzyme in rabbit experiments, with some mitochondria swelling and rupturing, which is part of why mortality rises at the end of winter. Sunlight, incandescent light, or laser red light all reactivate the copper at the heart of this enzyme. Frogs given a lethal dose of gamma rays survived unharmed if exposed to bright red light within the first hour.
-
Avoiding sunburn is the only real concern with sunlight, and PUFA in the skin is what makes it burn. In rabbit experiments, animals on a polyunsaturated diet developed quickly wrinkled, sun-damaged skin while animals on a saturated fat diet weren't hurt by the same exposure. The double bonds in PUFA act as antennas for ultraviolet light and then spread the damage as inflammatory mediators throughout the body. Without significant PUFA in the skin, the sun is largely a pure benefit.
-
Sunburn is a systemic poisoning, not just a local irritation. Even though the burn is absorbed within a few millimeters of skin, the inflammatory mediators that ooze from damaged skin into the bloodstream can cause general sickness, fever and effects in distant organs. The same principle applies to any local burn or to ionizing radiation: damage circulates and an X-ray of one body part produces estrogenic effects in the brain and ovaries.
-
Melanoma is largely not caused by sun exposure. Most melanomas occur in areas with less sun exposure: the back, the inside of the thighs, the bottoms of the feet. Melanoma rates have risen roughly 500% since 1940, paralleling the rise in dietary polyunsaturated fats, and have an inverse relationship with altitude. Ray has seen advanced metastatic melanoma regress on a diet shift plus coffee, aspirin, vitamin D, milk, and orange juice.
-
Most sunscreens are directly carcinogenic, and the phobia about ultraviolet has done real harm. Some sunscreens are carcinogenic in direct skin contact. The strict sun-avoidance message has driven rickets back into Northern England and pushed vitamin D deficiency conditions into the broader population. Cleaner alternatives are avoiding sunburn through diet, using coconut oil topically because saturated fat doesn't amplify UV the way PUFA does, applying topical aspirin or caffeine as free-radical scavengers, and supplementing vitamin D directly.
-
Vitamin D itself acts as a radiation-resistance factor in the skin. Once the 25-hydroxy form is in the protective range, melanin production ramps up before burning happens; tanning improves and burning decreases. Ray was super-sensitive to sun for most of his life and could get a red nose driving in a closed car through bright landscape, but after he raised his vitamin D he could spend hours at 7,000 to 8,000 foot altitude in Mexico without redness.
-
Darkness for more than the time it takes to sleep is itself harmful. Cortisol begins rising within fifteen minutes of lights off, and the cytochrome oxidase enzyme starts to fail after about eight hours of total darkness. People in northern winters, indoor workers and people working night shifts are essentially in chronic mild stress from this exposure. The remedy is bright light during waking hours on as much skin as possible.
-
Avoiding sunlight is worse than smoking two packs of cigarettes a day. A study on this comparison showed that the systemic damage from sun avoidance, including vitamin D deficiency, mitochondrial dysfunction, low testosterone, lowered metabolic rate, and elevated serotonin and cortisol, exceeds the damage of heavy smoking. People are scared away from the sun by fear of skin cancer and wrinkles, but the actual data on sun and disease incidence flips that fear on its head.
-
The sun produces 30,000 to 40,000 IU of vitamin D before saturation, far above any oral supplementation dose. UV-B in sunlight synthesises vitamin D in the skin, but the body has a feedback ceiling around 30,000 to 40,000 IU daily to prevent hypercalcemia. Beyond this, synthesis slows dramatically. This means sun-derived vitamin D is self-regulating, unlike high-dose oral supplementation which can drive soft-tissue calcification. The sun provides the right ratio of vitamin D synthesis (UV-B) and metabolic stimulation (red and infrared) that no artificial source matches.
-
95% of melatonin is produced subcellularly in mitochondria in response to near-infrared light, not at night by the pineal gland. The pineal gland synthesises about 5% of total melatonin in response to darkness. The remaining 95% is generated inside mitochondria in response to near-infrared exposure during the day. This means daytime sun exposure is essential for melatonin production, not just nighttime darkness. Healthy people with good thyroid function metabolise serotonin into melatonin efficiently because the conversion depends on ATP.
Notable Quotes
"If you avoid sunburn, the sun is going to be a pure benefit."
[Ray Peat — KMUD: Cancer Treatment]
"Many hours a day of white light, incandescent light, or sunlight, has many effects balancing the hormones, increasing your defensive hormones such as progesterone and testosterone."
[Ray Peat — KMUD: Heart Part 1]
"We shouldn't be in total darkness for longer than it takes to sleep."
[Ray Peat — KMUD: Cancer Treatment]
"Those little fluorescent things are going to cause an epidemic of cancer."
[Ray Peat — KMUD: Cancer Treatment]
"Avoiding sunlight is worse than smoking two packs of cigarettes a day. Think about that. Worse. Not similar."
[Georgi Dinkov — Restoring Glucose Utilization]
Important Things To Consider
Noon in summer can be too intense once any PUFA is present in the skin. Intermittent sunlight exposure spread over twelve to fifteen hours, with the brunt taken in morning and afternoon, is more useful than a single midday session for someone whose PUFA isn't already low.
High latitudes require more exposure to make vitamin D. At moderate latitudes between 10 AM and 2 PM in summer, fifteen to twenty minutes is enough. Outside that window or at higher latitudes, an hour or two is more realistic. Through winter at high latitudes, supplementation becomes essentially mandatory because UVB is too weak to convert cholesterol in the skin.
Aging skin produces about half the vitamin D from the same sunlight. Cholesterol synthesis declines with age in the skin, adrenals, gonads, and liver, so a 70-year-old needs about twice as much sun for the same vitamin D output as a young person. Statins block the cholesterol pathway upstream, compounding the deficit, and dark skin requires longer exposure than fair skin even at the same age.
Compact fluorescent (CFL) and standard fluorescent bulbs emit microwave and radio-frequency radiation. Ray considered them harmful to the nervous system. Disposal also creates a mercury problem. Incandescent bulbs are still the best general-purpose option, with LEDs as a possible alternative.
For winter, a 130-volt incandescent reflector bulb is the simple practical solution. Run on standard 120V household current, it produces an orange-shifted spectrum that is low in blue and rich in red and orange. 250-watt reflector bulbs, sometimes labeled "infrared", can keep skin and the work area warm for hours. Two or three of them aimed at where you sit is enough to keep a room biologically active and warm.
Tanning beds are not equivalent to sunlight. A tanning bed gives UV without the deep red light that systemically protects against it. With real sunlight, the red light penetrating throughout the body protects against the systemic bystander effects of any local burn. Tanning beds remove that protection and leave only the damaging fraction.
Bright light shining on closed eyes during sleep activates the hormonal system and depletes vitamin A. Ray noticed that sleeping with a bright reading lamp aimed at his face produced acne by morning, because the light reaching the retina activated steroid production and consumed the vitamin A used in making pregnenolone.
Aspirin taken about an hour before sun exposure prevents sunburn. Aspirin is a fast-acting lipid peroxidation preventer, faster than vitamin E. For people with high PUFA stores, an aspirin about an hour before exposure limits the sunburn reaction.
Vitamin E stored in fat tissue protects subcutaneous PUFA from UV peroxidation. Because vitamin E concentrates in fatty tissue and the liver, sufficient long-term vitamin E intake means there is enough antioxidant present in subcutaneous fat to neutralise UV-driven peroxidation. Vitamin E intake is inversely correlated with all three major types of skin cancer.
Sunrise and sunset hours have less UV-B if you want to limit burn risk while still getting red and infrared exposure. The infrared and red wavelengths still come through during these times, so the metabolic and mitochondrial benefits remain available without the UV peak that causes burning in fair-skinned or PUFA-loaded individuals. This is a useful starting point for people building up sun tolerance.