The Light We Were Never Meant to Live Without
Imagine you could trace a single thread through the labyrinth of modern chronic disease—obesity, autoimmunity, hormonal collapse, depression, metabolic dysfunction, accelerated aging—and discover they all converge at one overlooked point: a wavelength of light your ancestors received every single day of their lives
One that modern living has systematically stripped from your biology.
That wavelength is UVB.
And once you understand what its absence costs you at the cellular level, you will never look at daylight—or your indoor life—the same way again.
We Are Running an Uncontrolled Experiment on Ourselves
Here’s the uncomfortable truth:
We have taken a species whose physiology was forged under open sky for millions of years—and moved it indoors.
This isn’t just about steps-per-day or screen time. It’s about spectral starvation. The light environment bathing your skin and entering your eyes has fundamentally changed. And of all the wavelengths we’ve lost access to, UVB—the narrow band of ultraviolet radiation between 280 and 315 nanometers—may be the most consequential.
Why? Because UVB is the trigger for your body’s most sophisticated “sunlight-to-chemistry” pathway: vitamin D synthesis. And vitamin D, as you’ll see, is not a simple nutrient. It functions as a hormone—a master regulator influencing gene expression across virtually every tissue in your body.
But here’s what most people don’t realize:
Vitamin D is just the tip of the iceberg.
When UVB strikes your skin, your body doesn’t just produce vitamin D₃. It produces dozens of vitamin D-like compounds—photoproducts with their own biological activity that we’re only beginning to understand. Oral vitamin D supplements, no matter how high-quality, cannot replicate this cascade.
This is why I’ve come to view UVB as an environmental nutrient —one that has become scarce in modern life, with profound downstream consequences.
The Physics and Behavior of UVB Deprivation
To understand UVB deficiency, you have to understand that it’s a physics plus behavior problem.
Physics Limits UVB Before You Even Step Outside
At Earth’s surface, UVA dominates the ultraviolet spectrum—comprising 95 percent or more of terrestrial UV. UVB is a tiny fraction. And unlike UVA, which penetrates clouds and glass relatively easily, UVB is absorbed by the atmosphere at steep angles.
What does this mean practically?
If you live above approximately 35° latitude—that’s roughly the northern border of Florida—you cannot synthesize vitamin D from sunlight for five to six months of the year, no matter how long you stand outside.
The sun never climbs high enough above the horizon for UVB to reach you.
Even in tropical latitudes where UVB exists, it’s only available for a narrow window—roughly two to four hours centered on solar noon. And even then, UVB comprises only about 0.4-0.5 percent of the total spectrum.
Add in atmospheric pollution, geoengineering, and cloud cover, and UVB availability shrinks further still.
Modern Behavior Finishes the Job
But physics alone doesn’t explain our predicament. Our behavior seals it:
- Indoor living: Americans now spend less than 8% of their time outdoors—a figure that collapsed further during pandemic lockdowns
- Clothing coverage: Even in warm climates, most of us expose only our face and hands
- Windows: Glass filters out virtually all UVB while allowing UVA through—meaning that car commuters and office workers receive UVA (which accelerates aging) without the protective UVB that stimulates melanin production
- Sunscreen: Chemical sunscreens, while reducing burn risk, also dramatically reduce cutaneous vitamin D synthesis
- Shade-seeking and fear of the sun: Decades of public health messaging have taught us to treat sunlight as a carcinogen rather than a biological necessity
The result? A population that is profoundly UVB-deficient—even in sunny climates, even in summer months.
Biology Amplifies the Problem
Certain populations face even greater challenges:
- Darker skin pigmentation: Higher melanin content reduces the skin’s ability to produce vitamin D from available UVB
- Older age: The skin’s capacity for vitamin D synthesis declines with age
- Obesity: Vitamin D is fat-soluble and can be sequestered in adipose tissue, lowering circulating levels
- Malabsorption conditions: Gut dysfunction impairs both dietary and endogenous vitamin D utilization
This is not a failure of willpower. It’s a mismatch between our biology and our built environment—one with consequences we’re only beginning to fully appreciate.
Your Skin: A Solar-Powered Endocrine Organ
Most people think of skin as a wrapper—a barrier between inside and outside. But your skin is far more than that.
It’s an endocrine interface.
When adequate UVB reaches your skin, it initiates a multi-step synthesis cascade:
- Skin: UVB photons convert 7-dehydrocholesterol (a cholesterol derivative) into pre-vitamin D₃
- Liver: Pre-vitamin D₃ is hydroxylated into 25-hydroxyvitamin D [25(OH)D]—the main circulating form measured in blood tests
- Kidneys + peripheral tissues: 25(OH)D is converted to the active hormone 1,25-dihydroxyvitamin D (calcitriol)
- Cell nucleus: Calcitriol binds the vitamin D receptor (VDR), altering gene transcription
This is why vitamin D deficiency has such far-reaching effects. The VDR is expressed in virtually every cell type. Modern genomic research shows that active vitamin D can directly or indirectly regulate the expression of thousands of genes—with different programs activated in different tissues.
This isn’t hyperbole. Peer-reviewed research has identified 5,000-20,000 genomic loci bound by the VDR in the presence of its ligand. In immune cells alone, vitamin D signaling modulates hundreds of primary target genes.
When UVB is missing, this entire regulatory architecture is compromised.
The Downstream Costs of UVB Deficiency
Bone and Mineral Homeostasis: The Foundation
The most well-established consequence of vitamin D deficiency is skeletal. Without adequate vitamin D, calcium absorption plummets, leading to:
- Rickets in children (bone deformity, growth impairment)
- Osteomalacia in adults (bone softening, pain, fracture risk)
These conditions are preventable—and their existence in modern populations is a direct indictment of our sunlight-deprived lifestyles.
Immune Function: A Compelling Mechanistic Story
Beyond bone, the most intriguing research involves immunity.
Immune cells—macrophages, dendritic cells, T lymphocytes—possess the enzymatic machinery to locally activate vitamin D. When adequately supplied with circulating 25(OH)D, these cells can:
- Stimulate production of antimicrobial peptides like cathelicidin
- Support autophagy (cellular self-cleaning critical for fighting intracellular pathogens)
- Modulate inflammatory responses, suppressing pro-inflammatory Th1/Th17 pathways while supporting regulatory T cells
In UVB deficiency, immune cells lack the substrate they need for this local activation. The signaling system fails—not because the machinery is broken, but because the raw material is missing.
This may help explain observed associations between low vitamin D status and:
- Increased respiratory infection susceptibility
- Higher autoimmune disease incidence
- Impaired wound healing and tissue repair
The VITAL trial—one of the largest randomized studies of vitamin D supplementation—found that 2,000 IU/day was associated with a 22 percent reduction in confirmed autoimmune disease over five years (hazard ratio 0.78). While not definitive, this signal is consistent with the mechanistic picture.
Hormonal Regulation: The Testosterone Connection
During our recent webinar on this topic, Mitolux founder Guti Gutierrez shared his personal journey—including testosterone levels that collapsed in his 40s and then recovered without TRT through deliberate UVB and circadian light protocols.
His testosterone went from mid-300s to over 800 ng/dL at age 47—levels typically seen in teenagers.
This isn’t magic. It’s mechanism.
Testosterone synthesis involves cholesterol-derived pathways that interface with vitamin D metabolism. Adequate UVB, combined with proper circadian rhythm (itself regulated by light exposure), supports the endocrine environment necessary for optimal hormone production.
The same principles apply to female hormones—estrogen and progesterone are part of interconnected steroid hormone cascades that benefit from the same foundational inputs.
Metabolic Health: The Weight Connection
Research has demonstrated that UVB exposure can prevent weight gain through multiple mechanisms:
- Leptin regulation: UVB influences hunger signaling
- Nitric oxide release: Sunlight-induced NO improves vascular function and metabolic flexibility
- Circadian entrainment: Proper light exposure supports metabolic timing
A Swedish study followed 30,000 women for 20 years and found that those who avoided sun exposure had mortality rates similar to smokers—driven largely by cardiovascular and metabolic disease.
The headline was stark: “Avoiding the sun is as dangerous as smoking” I reported on this amazing study on GreenMedInfo.com here.
Cognitive Function and Mood
UVB deficiency doesn’t stay below the neck. Research links inadequate sunlight exposure to:
- Seasonal Affective Disorder (SAD)
- Depression and anxiety
- Cognitive decline in elderly populations
- Impaired learning and memory (via glutathione biosynthetic pathways in the brain)
This isn’t surprising when you consider that the brain is among the most metabolically demanding organs—and that vitamin D receptors are densely expressed in neural tissue.
Why Vitamin D Supplements Cannot Replace UVB
Here’s the inconvenient truth the supplement industry doesn’t advertise:
Oral vitamin D is one compound. UVB generates dozens.
When sunlight strikes your skin, it produces not just vitamin D₃, but a spectrum of photoproducts—vitamin D-like compounds that remain in your system and appear to serve as “reserves” the body can convert to active vitamin D as needed.
This explains a persistent finding in the research: vitamin D synthesized through sun exposure lasts longer in the body than vitamin D from supplements, and exists in its far more powerful sulfated form (which is not found in supplements).
It also explains why, despite widespread supplementation, we continue to see:
- Autoimmune disease rates climbing
- Metabolic syndrome epidemic
- Fertility collapse (both male and female)
- Depression and anxiety at all-time highs
Supplements address one downstream marker—serum 25(OH)D. But they cannot replicate the full biological program that UVB initiates.
This doesn’t mean supplements are useless. For those at high latitudes, during winter months, or with limited sun access, they remain an important tool.
But they should be understood as a floor, not a ceiling—a safety net, not a replacement for the evolutionary input we’re designed to receive.
See more here substack.com
Header image: Farringdon Osteopaths