UV Light, Nitric Oxide, and the Brain: How Sunlight Improves Cognitive Function Beyond Vitamin D

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The Missing Mechanism: What Sunlight Does That Vitamin D Supplements Cannot

There is a paradox in the sunlight-health literature that has puzzled researchers for years: populations with high sunlight exposure consistently show better cardiovascular health, lower blood pressure, reduced mortality, and improved cognitive function compared to low-sun populations. The standard explanation has been vitamin D — sunlight produces vitamin D, vitamin D is good for you, therefore sunlight is good for you. But here is the problem: vitamin D supplementation trials, while showing some benefits, have consistently failed to replicate the full magnitude of health improvements associated with actual sunlight exposure. Something else is going on. Sunlight is doing something that a vitamin D capsule cannot.

That something turns out to be nitric oxide.

In 2014, Dr. Richard Weller, a dermatologist at the University of Edinburgh, published a paper in the Journal of Investigative Dermatology that changed the conversation about sun exposure and health. Weller demonstrated that when human skin is exposed to ultraviolet A radiation (UVA, 315-400 nm) — the longer-wavelength UV that is present year-round, penetrates glass, and does not produce vitamin D — large quantities of nitric oxide are released from pre-formed stores in the skin. This UV-induced nitric oxide release is rapid (detectable within minutes), substantial (enough to measurably lower blood pressure), independent of vitamin D, and has profound implications for cardiovascular and neurological health.

The body stores nitric oxide in the skin as nitrate and nitrosothiol derivatives — bound to proteins, lipids, and other molecules in a stable but photolabile (light-sensitive) form. These stores are substantial: the skin contains an estimated 2-3 milligrams of nitric oxide equivalents per square meter, making the skin the largest reservoir of nitric oxide in the body. When UVA photons strike these stores, the energy of the photon breaks the chemical bond holding the nitric oxide in its stored form, releasing it into the bloodstream.

This is not vitamin D synthesis. It requires different wavelengths (UVA rather than UVB). It occurs through a different mechanism (photolysis of NO stores rather than photochemical conversion of 7-DHC). It produces a different product (nitric oxide rather than vitamin D3). And it has effects on the body that vitamin D supplementation does not replicate — particularly on blood pressure, cardiovascular function, and cerebral blood flow.

Nitric Oxide: The Master Signaling Molecule

To understand why UV-induced nitric oxide release matters for consciousness, you need to understand what nitric oxide does. NO is not just another signaling molecule. It is one of the most ubiquitous and versatile signaling molecules in biology — a gasotransmitter that diffuses freely through cell membranes, acts within seconds, and regulates an astonishing range of physiological functions.

Robert Furchgott, Louis Ignarro, and Ferid Murad shared the 1998 Nobel Prize in Physiology or Medicine for their discovery that nitric oxide is the endothelium-derived relaxing factor — the molecule that blood vessels use to regulate their own diameter. When nitric oxide is released by endothelial cells (the cells lining blood vessels), it diffuses into the surrounding smooth muscle cells, activates soluble guanylate cyclase, increases cyclic GMP, and causes the muscle to relax — widening the blood vessel and increasing blood flow.

But nitric oxide does far more than dilate blood vessels:

Neurotransmission. NO functions as a retrograde neurotransmitter in the brain — it is released by the post-synaptic neuron and diffuses backward to the pre-synaptic neuron, modulating the strength of the synapse. This mechanism is critical for long-term potentiation (LTP) — the cellular basis of learning and memory. Nitric oxide is essential for the formation of new memories.

Neuroplasticity. NO promotes the growth of new synapses and the remodeling of existing neural circuits. It activates signaling pathways (including the CREB transcription factor) that drive the expression of genes involved in synaptic plasticity.

Cerebral blood flow. NO is the primary regulator of cerebral blood flow — the delivery of oxygen and glucose to the brain. When neurons become active, they release NO, which dilates local blood vessels and increases blood flow to the active region (this is the mechanism underlying functional MRI — the fMRI signal detects the increase in blood flow that follows neural activity). Without adequate NO, cerebral blood flow is impaired, and the brain operates in a state of relative ischemia — receiving insufficient oxygen and glucose to support optimal function.

Mitochondrial function. At physiological concentrations, NO modulates mitochondrial respiration through reversible binding to cytochrome c oxidase (as discussed in the red light therapy article). At appropriate levels, this modulation is regulatory — it fine-tunes ATP production to match metabolic demand. At excessive levels (as in chronic inflammation), NO inhibits mitochondrial function — which is where photobiomodulation can help by dissociating excess NO from the enzyme.

Immune function. Macrophages and other immune cells produce large quantities of NO as a microbicidal agent — NO is directly toxic to bacteria, viruses, and parasites. This is the immune system’s chemical warfare capability.

Anti-inflammatory effects. At physiological concentrations, NO has anti-inflammatory properties, inhibiting leukocyte adhesion to blood vessel walls, reducing platelet aggregation, and modulating cytokine production.

The Weller Studies: Sunlight, Blood Pressure, and Mortality

Dr. Weller’s research has produced a series of findings that collectively challenge the “sun is dangerous” narrative that has dominated dermatological advice for decades:

Blood pressure reduction. In a 2014 randomized controlled study, Weller exposed volunteers to UVA radiation equivalent to 30 minutes of midday Mediterranean sun. The result: systolic blood pressure dropped by approximately 3-4 mmHg and remained reduced for 30-60 minutes. This reduction was not caused by skin warming (control experiments with heat lamps at the same skin temperature produced no blood pressure change). It was specifically caused by the photolysis of nitric oxide stores in the skin.

A 3-4 mmHg reduction in systolic blood pressure may seem modest, but at a population level, it is enormous. Epidemiological data suggest that a 2 mmHg population-wide reduction in systolic blood pressure would prevent approximately 10% of stroke deaths and 7% of deaths from ischemic heart disease. Weller has argued that the mortality benefit of sunlight exposure — mediated through NO-dependent blood pressure reduction — likely exceeds the mortality cost of sunlight exposure through skin cancer.

All-cause mortality. Weller’s argument is supported by a remarkable Swedish cohort study — the Melanoma in Southern Sweden (MISS) cohort — that followed 29,518 women for 20 years (Lindqvist et al., 2014, 2016, published in the Journal of Internal Medicine). The study found that women who actively avoided sun exposure had a life expectancy 0.6-2.1 years shorter than women with the highest sun exposure — even after accounting for the increased risk of skin cancer in the sun-exposed group. Sun avoidance was, statistically, a risk factor for death comparable to smoking.

The authors concluded: “Avoidance of sun exposure is a risk factor for death of a similar magnitude as smoking. Nonsmokers who avoided sun exposure had a life expectancy similar to smokers in the highest sun exposure group.”

This finding is extraordinary and profoundly under-reported. The public health message for decades has been to minimize sun exposure to prevent skin cancer. The epidemiological data suggest that this advice, while reducing skin cancer risk, may be increasing deaths from cardiovascular disease, metabolic syndrome, and other conditions linked to sunlight deficiency — by a margin that exceeds the skin cancer deaths prevented.

Cerebral Blood Flow: Sunlight Feeds the Brain

The connection between UV-induced nitric oxide and consciousness becomes clear when you trace the NO from the skin to the brain.

When UVA photons liberate nitric oxide from skin stores, the NO enters the bloodstream and is transported throughout the body. While NO has a short half-life (seconds in the bloodstream), it is continuously regenerated from circulating nitrite — a more stable transport form of NO that serves as a reservoir. Nitrite can be reduced back to active NO by deoxygenated hemoglobin, xanthine oxidoreductase, and acidic conditions — all of which are present in metabolically active tissues, including the brain.

The cerebral vasculature is exquisitely sensitive to nitric oxide. NO-mediated vasodilation is the primary mechanism by which the brain regulates its own blood supply. When sunlight exposure increases circulating NO and nitrite, cerebral blood flow increases — delivering more oxygen and glucose to neural tissue.

The consequences for cognitive function are direct:

Improved working memory. Working memory — the mental workspace used for reasoning, comprehension, and problem-solving — depends on sustained activity in the prefrontal cortex, one of the brain’s most metabolically demanding regions. Prefrontal function is exquisitely sensitive to blood flow: even modest reductions in cerebral perfusion impair working memory, while improvements in perfusion enhance it.

Enhanced attention. The brain’s attention networks — particularly the dorsal attention network spanning the frontal eye fields and intraparietal sulcus — require robust blood supply to maintain sustained focus. Inadequate cerebral blood flow produces the familiar experience of mental fatigue — the inability to concentrate despite wanting to.

Faster processing speed. The speed at which the brain processes information correlates with metabolic support — neurons that are well-supplied with oxygen and glucose fire more efficiently. Improved cerebral blood flow through NO-mediated vasodilation directly supports faster cognitive processing.

Mood elevation. The brain regions involved in mood regulation — the prefrontal cortex, anterior cingulate cortex, and amygdala — are sensitive to perfusion changes. Chronic cerebral hypoperfusion is associated with depression, and treatments that improve cerebral blood flow (including exercise and, potentially, sunlight exposure) have antidepressant effects.

Neuroprotection. Adequate cerebral blood flow is protective against neurodegeneration. Chronic cerebral hypoperfusion is increasingly recognized as a contributing factor to Alzheimer’s disease — not just as a consequence of neuronal loss but as a causal driver. The “vascular hypothesis” of Alzheimer’s, championed by researchers like Jack de la Torre, proposes that reduced cerebral blood flow precedes and contributes to the amyloid pathology, rather than merely resulting from it. If sunlight exposure, through NO-mediated cerebral vasodilation, helps maintain adequate cerebral blood flow, it may be protective against cognitive decline.

The Modern Sunlight Deficit

The implications of this research become alarming when you consider how little sunlight the average person in modern civilization receives.

Indoor living. Americans spend an average of 87% of their time indoors (EPA, National Human Activity Pattern Survey). Indoor lighting provides approximately 50-500 lux — 20 to 2,000 times less than outdoor daylight (10,000-100,000 lux). Window glass blocks virtually all UV-B and significantly attenuates UVA — meaning that even time spent near windows provides minimal UV exposure.

Sun avoidance behavior. Decades of public health messaging about skin cancer risk have produced a population that actively avoids sunlight, wears sunscreen (which blocks both UVB and, to varying degrees, UVA), covers skin with clothing, and remains indoors during peak UV hours. While preventing sunburn is reasonable, the pendulum has swung so far that sunlight deficiency is now a major public health problem.

Geographic concentration. The majority of the world’s economic activity occurs at latitudes above 35 degrees north — in regions where UV-B is insufficient for vitamin D synthesis for 3-6 months of the year and where total UV exposure is significantly reduced compared to equatorial regions.

The result: a global population that is chronically deprived of the UV radiation that drives both vitamin D synthesis and nitric oxide release — the two primary photochemical pathways through which sunlight supports human health. This deficiency manifests as:

• Epidemic vitamin D insufficiency (estimated 40-60% of the global population has suboptimal levels)
• Epidemic hypertension (1.28 billion adults worldwide, WHO 2021)
• Rising rates of cardiovascular disease, metabolic syndrome, and obesity in populations that have moved indoors
• Rising rates of depression, anxiety, and cognitive decline — particularly in high-latitude populations and urban environments with limited sun exposure
• Declining cognitive performance in aging populations — potentially accelerated by chronic cerebral hypoperfusion from NO deficiency

Nitric Oxide, Exercise, and the Synergy with Sunlight

There is an elegant synergy between sunlight exposure and physical exercise that amplifies the NO-consciousness connection.

Exercise independently increases nitric oxide production through the endothelial nitric oxide synthase (eNOS) pathway. When blood flows more forcefully through blood vessels during exercise — a phenomenon called shear stress — the endothelial cells that line the vessels respond by increasing eNOS activity and producing more NO. This exercise-induced NO production is a major mechanism by which exercise improves cardiovascular health, reduces blood pressure, and enhances cognitive function.

When exercise is performed outdoors in sunlight, two NO pathways are activated simultaneously:

1. Endothelial pathway (eNOS): Shear stress from increased blood flow → eNOS activation → NO production from the vessel wall
2. Cutaneous pathway (UV-photolysis): UVA photons → NO release from skin stores → systemic NO increase

The combined effect is additive — more NO, more vasodilation, more cerebral blood flow, more cognitive benefit. This explains the consistent finding in exercise psychology that outdoor exercise produces greater mood and cognitive benefits than equivalent-intensity indoor exercise. It is not just the psychological effects of being in nature — it is the photochemistry. The sun is adding NO to what the exercise is already producing.

The practical implication is clear: exercise performed indoors on a treadmill is good. Exercise performed outdoors in sunlight is significantly better — not because of vague “wellness” benefits but because of a specific photochemical mechanism that increases the vasodilatory NO signal reaching the brain.

Beyond Blood Flow: NO and the Gut-Brain Axis

Nitric oxide plays critical roles in the gut that have indirect but significant effects on consciousness:

Gut motility. NO is the primary inhibitory neurotransmitter of the enteric nervous system — the “second brain” containing over 500 million neurons that controls gut movement. Adequate NO levels support healthy peristalsis and gut motility. NO deficiency contributes to gastroparesis, constipation, and irritable bowel syndrome.

Gut barrier integrity. NO helps maintain the integrity of the intestinal epithelial barrier — the single layer of cells that separates the gut contents (bacteria, food particles, toxins) from the bloodstream. When NO levels are insufficient, the gut barrier becomes permeable (“leaky gut”), allowing bacterial endotoxin (lipopolysaccharide, LPS) to enter the bloodstream and trigger systemic inflammation — including neuroinflammation, which directly degrades cognitive function and mood.

Gut microbiome. NO modulates the composition of the gut microbiome, which in turn influences brain function through the production of neurotransmitters (serotonin, GABA, dopamine), short-chain fatty acids, and inflammatory mediators. The gut-brain axis — the bidirectional communication network between gut and brain — is profoundly influenced by nitric oxide levels.

This gut-brain-NO pathway provides another mechanism by which sunlight deficiency impairs consciousness: insufficient UV exposure → reduced NO → impaired gut barrier → increased endotoxin translocation → systemic and neuroinflammation → brain fog, mood disruption, and cognitive decline.

The Spiritual Dimension: Sun as the Source of Life Force

Every culture that has lived under the sun has recognized it as more than a source of warmth and light. The sun is universally associated with life force — the animating energy that distinguishes living organisms from dead matter:

• Prana in the Vedic tradition: the life force absorbed from sunlight through the breath and the skin. The practice of surya namaskar (sun salutation) is explicitly designed to absorb solar prana at dawn.

• Ra in Egyptian tradition: the sun god whose daily journey across the sky sustains all life. The pharaoh’s connection to Ra was understood as a direct channel of life force.

• Inti in the Incan tradition: the sun deity whose warmth and light sustained the Quechua people. The Inti Raymi festival celebrated the sun’s return at the winter solstice.

• Shamash in Mesopotamian tradition: the sun god who was also the god of justice and truth — connecting solar energy with clarity of perception and moral discernment.

• Sungazing traditions: Found across cultures — the practice of looking at the rising or setting sun to absorb its energy. While the safety of direct sun-gazing is debated, the tradition reflects a universal intuition that the eye is a portal through which solar energy enters the body and brain.

These traditions are not primitive attempts to explain photochemistry. They are phenomenological descriptions of an experience: when you stand in sunlight, something enters your body that increases vitality, clarity, and the felt sense of being alive. Modern photobiology has identified two major molecular mediators of this experience — vitamin D and nitric oxide — and has traced their pathways from skin to bloodstream to brain. But the subjective experience of standing in sunlight — the warmth, the brightening of mood, the sharpening of perception, the feeling of energy entering the body — is the same experience the ancients described. The mechanism explains the experience. The experience validates the mechanism.

When a yogi describes absorbing prana from the sun, they are describing — in experiential rather than molecular language — the absorption of UV photons by skin, the photolysis of nitric oxide stores, the increase in cerebral blood flow, and the resulting enhancement of cognitive function and vitality. The language is different. The reality is the same.

Practical Protocol: Optimizing UV-Nitric Oxide Release

Based on the current research, a practical protocol for optimizing the UV → NO pathway includes:

Daily sun exposure:

• Target 15-30 minutes of direct sunlight on exposed skin (arms, legs, face) during peak UV hours (typically 10 AM - 2 PM)
• UVA exposure is the primary driver of NO release, and UVA is present year-round at most latitudes (unlike UVB)
• UVA penetrates cloud cover and light clothing more effectively than UVB
• No sunscreen during this window — sunscreen blocks both UVB and UVA
• Adjust duration based on skin type — the goal is sub-erythemal exposure (no redness or sunburn)
• Gradual tanning builds melanin, which provides protection against UV damage while still permitting NO release

Dietary nitrate support:

• The skin’s NO stores are replenished in part from dietary nitrate, which is converted to nitrite by oral bacteria and then to NO stores in skin and blood vessels
• Nitrate-rich foods: beetroot, arugula (rocket), spinach, celery, lettuce, radish
• Beetroot juice is one of the most studied dietary NO precursors, with documented effects on blood pressure reduction and exercise performance
• Do not use antibacterial mouthwash — it kills the oral bacteria (particularly Veillonella and Actinomyces species) that convert dietary nitrate to nitrite, and research has shown that mouthwash use abolishes the blood pressure-lowering effects of dietary nitrate

Exercise in sunlight:

• Combine the eNOS (exercise) and cutaneous (UV) pathways by exercising outdoors during daylight hours
• Morning outdoor exercise provides both UV-NO release and melanopsin-mediated circadian entrainment — a dual-pathway optimization
• Even walking outdoors provides meaningful UV exposure and light exercise

Nasal breathing:

• The paranasal sinuses produce nitric oxide continuously at concentrations 100 times higher than in the mouth
• Nasal breathing delivers this sinus-produced NO directly to the lungs, where it enhances oxygen absorption and acts as a local antimicrobial
• Mouth breathing bypasses this pathway entirely
• The yogic practice of pranayama, which emphasizes nasal breathing, may be partly effective through NO delivery to the respiratory system

Skin care considerations:

• The skin’s NO stores are located in the epidermis and dermis
• Chronic sunscreen use reduces these stores over time by preventing the UV exposure that stimulates their replenishment
• A balanced approach: use sunscreen on the face and areas prone to photoaging and skin cancer (nose, ears, tops of hands), but allow regular sub-erythemal UV exposure on larger body areas (torso, legs, arms) to maintain NO stores
• After sun exposure, the antioxidant-rich compounds in the skin (vitamin E, vitamin C, carotenoids) protect against UV damage while the NO has already been released

The Sunlight Deficit of Modern Life: An Evolutionary Perspective

The human organism is a solar-powered system. Not in the metaphorical sense — in the photochemical sense. UV-B photons convert 7-DHC to vitamin D, which controls 2,000 genes. UVA photons release nitric oxide from skin stores, which dilates blood vessels and improves blood flow to every organ. Visible blue photons activate melanopsin, which sets the circadian clock. Red and near-infrared photons activate cytochrome c oxidase, which increases mitochondrial ATP production.

Every one of these pathways requires direct exposure to sunlight — not through glass, not through clothing, not through sunscreen. The modern human, spending 87% of their time indoors, behind glass, under artificial light, covered in UV-blocking chemicals, is running a solar-powered system on battery backup. The battery — endogenous NO production by eNOS, dietary nitrate intake, vitamin D supplementation — can sustain basic function. But it cannot replicate the full photochemical symphony that the sun provides.

The result is not a single disease. It is a general degradation of every system that depends on photon input — which is every system. The cardiovascular system runs on NO deficiency. The endocrine system runs on vitamin D deficiency. The circadian system runs on light deficiency. The mitochondrial system runs on photon deficiency. And consciousness — the emergent property of all these systems working together — runs dim, foggy, restricted, and fragile.

The solution is embarrassingly simple: go outside. Stand in the sun. Let the photons reach your skin and your eyes. Not for hours — for minutes. Not with the goal of tanning or burning — with the goal of feeding the photochemical pathways that your biology depends on. The sun is not your enemy. The sun is the power supply for the biological operating system you call your body. The idea that you should avoid it — that you should live your life behind glass and under fluorescent lights, protected from the electromagnetic radiation that every cell in your body evolved to receive — is one of the most consequential errors in the history of public health.

The ancient sun worshippers were not naive. They were observant. They noticed that sunlight made them feel alive, clearheaded, vital, and strong. They noticed that prolonged darkness made them dull, weak, depressed, and sick. They built their spiritual practices around these observations. And modern photobiology has confirmed every single one of them — at the molecular level, with the mechanisms mapped, the pathways identified, and the clinical data published.

The sun is the original medicine. Nitric oxide is one of its prescriptions. And the brain — hungry for blood flow, for oxygen, for the molecular signals that support clarity and awareness — is waiting for the photons that have been feeding consciousness since life began.

Key Researchers and References

• Richard Weller — University of Edinburgh. UV-induced nitric oxide release from skin, blood pressure reduction. Published in Journal of Investigative Dermatology (2014).
• Pelle Lindqvist — Karolinska Institute. MISS cohort study: sun exposure and all-cause mortality. Published in Journal of Internal Medicine (2014, 2016).
• Robert Furchgott, Louis Ignarro, Ferid Murad — Nobel Prize 1998 for discovery of nitric oxide as a signaling molecule.
• Nathan Bryan — Baylor College of Medicine. Nitric oxide, oral microbiome, and cardiovascular health.
• Martin Feelisch — University of Southampton. Sunlight, nitric oxide, and cardiovascular mortality.
• Jack de la Torre — University of Texas at San Antonio. Vascular hypothesis of Alzheimer’s disease.
• Key papers: Liu D et al. (2014) “UVA irradiation of human skin vasodilates arterial vasculature and lowers blood pressure independently of nitric oxide synthase.” J Invest Dermatol. Lindqvist PG et al. (2014) “Avoidance of sun exposure is a risk factor for all-cause mortality.” J Intern Med.