Using Light (Sunlight, Blue Light & Red Light) to Optimize Health | Huberman Lab Essentials

Light absorbed by intrinsically photosensitive ganglion cells in the eyes directly inhibits melatonin production from the pineal gland. This mechanism allows the body to track the time of day and year, influencing seasonal biological functions like bone mass, gonad maturation (suppressed by high melatonin in children), and placental development. Melatonin levels are naturally higher in winter months due to less light exposure, signaling seasonal changes to the body.

Light activates melanopsin cells, which shut down pineal gland melatonin production. Melatonin acts as a calendar system, with higher release in winter months in the northern hemisphere, impacting bone mass and gonad maturation.

Exposure of the skin to UVB light (ultraviolet blue light) triggers increases in testosterone and estrogen in both mice and humans. This effect is distinct from light exposure to the eyes and leads to maintained proper hormone ratios, increased desire to mate, and enhanced fertility indices like follicle maturation in females.

A study in 'Cell Reports' showed that UVB exposure to skin in mice and humans increased testosterone and estrogen, and in mice, led to increased mating behavior and gonadal weight. In human females, it enhanced follicle maturation.

UVB light exposure, both to the skin and eyes, increases the body's tolerance for pain. This occurs through the release of endogenous opioids like beta-endorphins, which act as natural painkillers by modulating neurons in the periaqueductal gray area of the midbrain.

Studies published in 'Neuron' and 'Skin Exposure to Ultraviolet B' demonstrated that UVB light increases beta-endorphin release and activates a visual circuit connected to the periaqueductal gray, leading to reduced pain perception.

Sufficient UVB light exposure to the eyes activates the sympathetic nervous system, which in turn signals the spleen to deploy immune cells and molecules. This prepares the immune system to combat infections more effectively, explaining why people might experience fewer infections during longer, sunnier days.

UVB light arriving on the eyes triggers activation of sympathetic nervous system neurons, leading to the spleen deploying immune cells and molecules to combat infection.

UVB exposure to both the eyes and skin stimulates the turnover of stem cells in hair, skin, and nails. This results in faster hair growth, more youthful-looking skin (by replacing older cells with new ones), and stronger nails, particularly during periods of longer daylight.

A 'Proceedings of the National Academy of Sciences' study showed that melanopsin cells in the eyes are critical for triggering stem cell turnover in skin, hair, and nails, leading to increased growth and renewal in longer days.

Exposure to bright light, especially UVB, between 10 PM and 4 AM activates a specific neural circuit from the eyes to the perihabenular nucleus, bypassing circadian clocks. This activation reduces dopamine output and other feel-good molecules, potentially leading to a decrease in mood and increased risk of depression.

Viewing UVB light at night activates the eye-to-perihabenular pathway, which truncates or reduces dopamine release, negatively impacting mood.

Long-wavelength red and near-infrared light can penetrate deep into the skin, reaching mitochondria within cells. This activates mitochondria, increasing ATP production and reducing reactive oxygen species (ROS). This cellular rejuvenation process improves skin quality, accelerates wound healing, and helps remove scars or unwanted pigmentation.

Red and infrared light pass into deeper skin layers, activating mitochondria to increase ATP and reduce reactive oxygen species, which are detrimental to cell function. This mechanism underlies red light therapies for skin healing and improvement.

Viewing red light (around 670 nanometers) for 2-3 minutes daily, within the first three hours of waking, can significantly improve visual function in individuals aged 40 and older. This occurs by reducing reactive oxygen species and cholesterol deposits (drusen) in the metabolically active retinal cells, effectively reversing some aspects of neuronal aging.

Dr. Glenn Jeffrey's lab at University College London showed that 2-3 minutes of 670nm red light exposure daily improved visual acuity by 22% in subjects 40-72 years old, by reducing ROS and drusen in retinal cells.