The episode features Dr. Glenn Jeffrey, professor of neuroscience at University College London, discussing how specific wavelengths of light can improve health through mitochondrial function.

Dr. Jeffrey explains his research on red, near-infrared, and infrared light's effects on vision, blood sugar regulation, metabolism, and cellular aging, including mechanisms by which light penetrates tissue and supports mitochondria.

The conversation covers the public health implications of modern LED lighting, which lacks long wavelengths present in sunlight and incandescent bulbs, potentially contributing to metabolic dysfunction and accelerated aging.

Host Andrew Huberman, professor of neurobiology and ophthalmology at Stanford, guides the discussion through practical applications including optimal timing for light exposure, device recommendations, and simple zero-cost interventions for improving indoor lighting environments.

Light Spectrum Basics and Evolutionary Context

Visible light spans 400-700 nanometers, but sunlight extends from 300 nanometers (ultraviolet) to nearly 3,000 nanometers (infrared), creating a continuous spectrum far beyond human vision.

"Short wavelength lights, the ones just below blue, they're very, very high frequency, they carry quite a kick" causing sunburn because energy concentrates at the skin surface rather than penetrating - Glenn

The human lens and cornea block ultraviolet wavelengths, which is why we don't see them, but excessive UV exposure over time causes cataracts described as the lens being "cooked" with visible browning.

Cataract surgery involves replacing the clouded lens with a clear plastic lens containing UV blockers, causing patients to initially perceive everything as "very bright" and "sparkly" before the brain re-adapts within two days.

Color perception works through reflection and absorption: blue ocean water absorbs long wavelengths and reflects short wavelengths back, while red objects do the opposite, reflecting long wavelengths.

Sunlight Exposure and All-Cause Mortality

Research by Richard Weller from Edinburgh shows all-cause mortality is lower in people with substantial sunlight exposure, with cardiovascular disease and cancers as flagship conditions, not the expected skin-related issues.

"The only thing you've got to avoid is sun burn" for DNA mutations, while Aborigines in Australia don't get skin cancer despite high sun exposure, suggesting evolutionary adaptation - Glenn on Weller's research

Skin cancer patients show relatively low vitamin D levels rather than the expected high levels if skin cancer were directly caused by sunlight, challenging conventional assumptions about sun exposure risks.

The most deadly melanomas are not associated with sun exposure and often occur on body parts with minimal sunlight contact, such as between toes, as illustrated by Bob Marley's case.

Studies from Sweden and University of East Anglia involving "very big numbers" show solid correlations between sunlight exposure and reduced all-cause mortality, though more research is needed to understand mechanisms.

How Long Wavelength Light Affects Mitochondria

Tina Karew in Russia first proposed that mitochondria absorb long wavelengths of light, though she was "very largely ignored" initially and Jeffrey would "love to buy her a glass of champagne" for starting the field.

Mitochondria don't directly absorb long wavelength light; instead, the nanowater surrounding them absorbs it, reducing viscosity and increasing the spin rate of ATP-producing motors that generate body weight in ATP daily.

"The motor starts to go around a little faster" as an immediate effect, then "something detects the speed of that train and says, lay down more tracks" causing increased synthesis of energy-producing proteins - Glenn

Long wavelength light absorption correlates tightly with water absorption patterns, including "water holes" where absorption is higher, explaining why this mechanism works across all tissues containing water.

Mitochondria evolved as independent bacteria in water environments before being co-opted by eukaryotic cells, explaining why they respond to wavelengths that water absorbs most effectively.

Long Wavelength Light Penetration Through Body

Long wavelength light passes completely through the human body with only "a few percent" emerging from the back, meaning the vast majority is absorbed and scattered internally affecting all tissues - Glenn

"It goes through the skin" and "literally go through the bone" including the skull, as demonstrated by physicist Bob Fosbury's measurements showing bones are not visible under long wavelength light - Glenn

Long wavelength light passes through six layers of t-shirt clothing with color making "no difference whatsoever," allowing therapeutic effects even when fully clothed outdoors.

Light scatters extensively inside rooms and bodies: "It's bouncing all around the room. It's coming in from a different angle and different parts of your body" beyond just the point source - Glenn

Biomedical engineer Ilyas Takhtanid passes red light through neonates' heads after stroke, measuring it on the other side as a metric of mitochondrial function that predicts survival rates.

Deoxygenated blood absorbs long wavelength light, creating "fantastic pictures of your veins" in hands and heads, while oxygenated tissue and bone allow light to pass through unimpeded.

Blood Glucose Regulation Through Red Light

The idea originated from Mike Powner during a 5 AM drive: "If we make mitochondria work harder, then they need glucose" leading to the hypothesis that red light would reduce blood glucose spikes.

Initial bumblebee experiments showed red light prevented blood glucose elevation after glucose feeding, while blue light caused "very high" glucose levels by slowing mitochondrial function.

Human subjects received a burst of red light before drinking glucose, then had finger pricks at regular intervals. "The reduction in the spike was of the order of just over 20%" - Glenn

Red light was shone on a small 4x6 inch rectangle on the back, far too small for local mitochondria alone to cause the effect, demonstrating that "mitochondria act as a community" across the body.

"It takes them a little time to have a conversation about it, but they act together" with the one to two hour experimental timeframe being "long enough for them to hold that conversation" - Glenn

John Metrofanes reduced Parkinson's symptoms in primates by shining red light on the abdomen, not the brain, further demonstrating systemic mitochondrial communication and reduced cell death signaling.

Vision Improvement Studies in Aging Adults

Retinas contain more mitochondria than any other body tissue with the highest metabolic rate, aging fast like "the sports car" that "after so many thousand miles, you've got to service it, otherwise it falls apart" - Glenn

Subjects viewed colored letters in visual noise to find detection thresholds, then received red light exposure. "Their threshold had improved in every one of those subjects by one. They could see something they couldn't see before" - Glenn

The improvement averaged around 20% across populations, though individual responses varied enormously with only one subject showing no improvement across large numbers tested.

Initial protocol used 670 nanometer red light for three minutes daily, chosen because "all the studies before us doing different things had used 670" providing an existing database for comparison.

"It makes very little difference" whether eyes are open or closed during exposure because long wavelength light passes through eyelids without significant attenuation - Glenn

Effects lasted exactly five days across flies, mice, and humans, suggesting "something very fundamental that is conserved across evolution is playing a role here" - Glenn

"There's not a dose response curve here. You put enough energy in at a certain wavelength of light and it goes bang and click. And then five days later, it goes chunk and stops" - Glenn

Optimal Timing and Wavelength Specifications

"Your biggest effect is always in the morning" from just before perceived sunrise until about 11 o'clock, consistent across flies, mice, and humans - Glenn

Morning is when bodies make more ATP than any other time, with hormone levels and blood sugar changing dramatically as the body prepares to be active rather than vulnerable like "a lizard that's got to wait for the sun to rise."

"In the afternoon, well, the standard lab joke is they're doing the ironing" as mitochondria perform other essential functions like contacting the endoplasmic reticulum rather than energy production - Glenn

Wavelengths below 670 toward 650 nanometers show "somewhat reduced" effects, while "pretty much anything will" work in the 670-900 nanometer range including near-infrared.

Original experiments used 40 milliwatts per centimeter squared, which is "very bright" and causes wincing, but effects occur at comfortable 8 milliwatts and even down to 1 milliwatt with depleted batteries.

Sunlight provides incomparable benefits as "an enormous broad spectrum" that cannot be replicated by single-wavelength devices, though specific wavelengths can address particular issues - Glenn

Macular Degeneration and Disease Intervention

"If I get you all to live to 100 years, probably 20% of you will have macular degeneration" as the retina "burns out" like a sports car - Glenn

Initial clinical trial on macular degeneration patients showed "absolutely no effect whatsoever" causing significant discouragement, but their husbands used as controls showed substantial improvements.

"The disease had gone beyond a certain point" in the patient group, while replicated studies starting earlier in disease progression "started to get a really good result" - Glenn

"Red light can impact on aging, it can impact on disease, but it can't do it if that disease has really gone" requiring early intervention before significant tissue damage - Glenn

Rheumatoid arthritis treatment showed "absolutely zero effect" because subjects already had twisted hands, when intervention should have occurred at first signs of hand aches before structural changes.

Over life, people lose a third of rod photoreceptors, but daily red light exposure in aging animals "reduced the pace of cell death in the retina" through mitochondrial support preventing apoptosis signals.

LED Lighting as Public Health Crisis

"This is an issue on the same level as asbestos. This is a public health issue and it's big" according to a group of scientists who are now speaking publicly - Glenn

LEDs won Nobel Prizes for energy efficiency but have "a big blue spike" and "no red" unlike billions of years of evolution under broad-spectrum sunlight, fires, and candles.

"When we use LEDs, the light found in LEDs, when we use them, certainly when we use them on the retina looking at mice, they're far less responsive" with declining membrane potentials and poor mitochondrial breathing - Glenn

Mice under LED lighting gain significant weight because "their mitochondria are not taking that glucose out and it's being deposited" as fat due to unbalanced blood glucose control.

LED-exposed mice develop fatty livers with smaller livers, kidneys, and hearts, plus elevated ALT proteins indicating liver distress, and abnormal sperm morphology with reduced swimming capacity.

Lifespan growth in Western Europe shows "a dent in the curve and the tendency towards asymptote" after 2010, potentially related to LED adoption though COVID complicates analysis.

Commercial buildings use infrared-blocking glass for thermal regulation, creating a "double hit" of restricted-spectrum LEDs plus isolation from outdoor infrared light through windows.

"The last thing to go in after the glass" in building construction is lighting, where budget overruns lead to purchasing "the cheapest LEDs" with the most restricted spectrum - Glenn

Screen Light and Myopia in Children

Jeffrey and colleagues "sat with a blue screen staring at it all day for days" and found "almost no effect" because screen blue is "rather long wavelength blue" around 450+ nanometers, outside the danger zone of 420-440.

Pediatric ophthalmologists are "very concerned" about close work combined with screen time driving myopia, particularly severe in Asia and China where it's become a major public health issue.

"The absence of long wavelength light is a driver" of myopia though the mechanism remains unclear, requiring pragmatic supplementation even without complete understanding - Glenn

Myopia causes eye elongation that stretches the retina, and "as the retina stretches as you age and you lose cells, so the retina thins" creating serious vision problems by ages 40-50.

Chinese classrooms use desk bars preventing children from sitting too close to read, and some use laser treatments that show "spots in the retina where the laser has affected negatively" by burning tissue.

Laser light "does not scatter evenly when it hits tissue. It forms something called caustics" with energy "tripling or quadrupling in certain areas" making it dangerous for myopia treatment - Glenn

Incandescent Bulbs Versus LED Devices

Architectural model makers given incandescent bulbs showed improvement in both blue and red color perception "to the same extent, and it was very significant" unlike LEDs which only improved blue perception.

The improvement from incandescent exposure "was maintained" at six days and one month later, far exceeding the five-day effect from narrow-spectrum LED red lights.

"The mitochondria knows that it's a compressed load of LEDs" and doesn't respond as well as to smooth-spectrum incandescent light, though the mechanism is "completely and utterly beyond me" - Glenn

Sunlight and incandescent bulbs provide smooth wavelength transitions from short to long, while LEDs have spikes that mitochondria can somehow detect and respond to differently.

"To a first approximation, the spectrum of light that you get from an incandescent light bulb is highly similar to solar light" covering almost the same range - Glenn

Many commercial red light devices are "pretty poor" with low-quality components, LEDs that aren't actually 670 nanometers as claimed, and degradation over time with repeated use.

"The majority of them do no harm" and "the majority of them have a positive impact" though quality varies significantly between medical-grade and consumer devices - Glenn

Practical Recommendations and Zero-Cost Solutions

"Get a dog because you'll have to go out in daylight two or three times a day" ensuring regular outdoor exposure to balanced spectrum sunlight - Glenn

Halogen lamps in kitchens during morning routines provide full-spectrum light at critical times, appearing as "ordinary white light" but containing balanced wavelengths including infrared.

Dimming halogen bulbs increases infrared output and "the bulb will last almost forever" while reducing energy costs, making it economically viable for evening use without disrupting melatonin.

"All plant matter reflects infrared light" with leaves staying cool in 80-degree heat by reflecting wavelengths near therapeutic doses, making strategic tree planting around buildings beneficial.

A Midwest city planted trees and measured stress biomarkers including complement-related proteins, finding "significant reduction" two to three years later in systemic inflammation markers.

Architects now consider planting on north sides of tall buildings to reflect light back through windows, and using incandescent heat sources in nursing homes for dual light and warmth benefits.

"We can affect public health and we should affect public health at a highly economic way" focusing on minimum effective interventions like single halogen bulbs rather than expensive overhauls - Glenn

Pure beeswax candles provide long wavelength light at minimal cost for evening reading or desk work, though safety precautions against fire are essential.

Mitochondrial Disease Clinical Applications

Children with genetic mitochondrial diseases where "the genetic code in the mitochondria have got their own DNA" can experience severe disability with many not surviving beyond age 25 from heart failure.

First child treated for ptosis (inability to open eyelids) had "gut-wrenching" positive results with "semi-mobility" within a month and a video showing her "walking to school" - Glenn

"I went to the bathroom and sobbed" after seeing the first child's improvement, representing a profound impact on quality of life for severely affected patients - Glenn

Clinical trial had to be wrapped up and funding returned because "we couldn't get enough kids into the study" due to low disease density and some children being "just so sick" to transport for assessment.

"Red light should help kids with mitochondrial disease. It will do absolutely no harm whatsoever" making it worth trying even without complete clinical trial data - Glenn

Upcoming trial for retinitis pigmentosa at Moorfields Eye Hospital will test changing light bulbs for patients, leveraging "the biggest ophthalmic outpatient population in the world" with sufficient patient numbers.

New Moorfields hospital building "looks great" but "blocks infrared" with glass and will have "the world's worst LEDs put in it" despite being a leading eye hospital - Glenn expressing frustration