New Study Finds Sunlight Benefits, Even Through Clothes, Improve Mitochondrial Function and Eyesight

You know that deep feeling of warmth that comes with sitting in the sun for a few minutes? It turns out it is deeper than we think. We've known for some time that natural sunlight is important for not only vitamin D production, but all the associated co-factors. Similarly, the entire wavelengths of sunlight, including the infrared, are involved in this complex ability for synthesis in the skin. 

We need the full spectrum of rays for proper Vitamin D metabolism. It starts with ultraviolet B (UVB) radiation from the sun (wavelengths between 290–315 nm) that initiate conversion of 7-dehydrocholesterol, a compound found in the skin, into pre-vitamin D3. This changes into vitamin D3 (cholecalciferol) over a period of several hours (Holick, 2007).

But here’s the kicker: vitamin D3 is biologically inactive at this point. It requires two more steps: First in the liver, where it becomes 25-hydroxyvitamin D (25(OH)D, also called calcidiol), Then in the kidneys, where it becomes 1,25-dihydroxyvitamin D (1,25(OH)₂D, also called calcitriol) — the active hormone.

And for these steps to occur efficiently, the body needs several key cofactors — magnesium, zinc, boron, vitamin A, vitamin K2, and more.

Sunlight helps with the function and absorption of many of these too.

Essential Cofactors for Vitamin D Function — and How Sunlight Supports Them

Magnesium: UVB exposure stimulates nitric oxide and affects parathyroid hormone (PTH) levels, which in turn regulate magnesium transport. Sun exposure may also help maintain circadian rhythms, indirectly supporting renal magnesium retention (Sakaguchi et al., 2018).

Zinc: The Enzyme Activator. Zinc is necessary for the function of many enzymes, including 25-hydroxylase and 1-alpha-hydroxylase, the enzymes responsible for converting vitamin D to its active forms. A 2020 study in Nutrients showed zinc modulates vitamin D receptor (VDR) expression and activity (Cheng et al., 2020).How sunlight helps: Exposure to sunlight boosts levels of melatonin and serotonin, which modulate inflammation and may influence zinc absorption and utilization via gut-brain axis regulation.

Vitamin K2: The Calcium Chaperone. Vitamin D increases calcium absorption, but without vitamin K2, that calcium may be misdirected into arteries instead of bones. K2 activates proteins like osteocalcin and matrix Gla-protein, which guide calcium to the right places. A review in Frontiers in Nutrition (2017) confirms this synergistic relationship (van Ballegooijen et al., 2017). How sunlight helps?  Emerging research suggests UV exposure stimulates certain gut bacteria involved in K2 production. Also, adequate sunlight supports skin cholesterol metabolism, which underpins K2’s menaquinone synthesis in peripheral tissues.

Vitamin A: Balancing Hormonal Activity. Vitamin A works synergistically with vitamin D at the receptor level. Both vitamins bind to nuclear receptors (VDR and RAR/RXR) and regulate gene expression. Overactivation of one without the other can cause imbalance. A study in The Journal of Nutrition (2006) shows that vitamin A enhances vitamin D’s regulation of calcium and phosphate metabolism (Zhang et al., 2006). How sunlight helps: Natural sunlight boosts retinal health and melatonin signaling, indirectly affecting vitamin A metabolism and transport. Also, UVB can influence liver enzymes responsible for converting retinol to retinal and retinoic acid.

Boron: The Underappreciated Modulator: Boron stabilizes and extends the half-life of vitamin D in the bloodstream, and it supports magnesium and calcium balance. A study in Biological Trace Element Research (2011) showed boron supplementation increases plasma levels of 25(OH)D (Nielsen, 2011).How sunlight helps: Solar infrared exposure may influence bone metabolism and parathyroid hormone (PTH) regulation, indirectly maintaining boron-related calcium homeostasis.

Why This Cofactor Symphony Matters

Taking large doses of vitamin D without the accompanying cofactors can be ineffective—or even harmful. For instance:

• Without magnesium, vitamin D may remain inactive, leading to symptoms of deficiency despite supplementation.
• Without vitamin K2, calcium absorption increases but so does vascular calcification risk.
• Without zinc, the body may struggle to activate vitamin D at all.

The presence of all these nutrients — many of which are supported or modulated by solar exposure — allows vitamin D to perform its full range of functions: calcium balance, immune modulation, gene expression, and many others.

Natural sunlight is not merely a trigger for cholecalciferol production. It plays a central role in orchestrating a complex, interdependent system that includes several cofactors. Together, these elements form a finely tuned physiological symphony. Supporting all aspects of this system — not just by taking vitamin D pills, but also by getting responsible sunlight exposure and consuming a nutrient-rich diet — is the key to unlocking the full power of vitamin D.

New Study Finds Benefits to Sunlight, Even Through Clothes

A new study published in Scientific Reports confirms what animal experiments have long hinted: that longer wavelengths of sunlight—especially in the infrared range (830–860 nm)—can penetrate deeply into the human body, enhance mitochondrial function throughout the body, and measurably improve vision—even without exposing the eyes directly to light. 

Study Overview

Researchers led by Glen Jeffery at University College London presented evidence that:

• Infrared sunlight passes through tissue: In direct midday sun, irradiance readings placed a radiometer against participants’ torsos and detected significant penetration of long-wavelength light .

• 830–860 nm LED exposure mimicking sunlight: Lab trials delivered 15-minute exposures to subjects' backs—fully clothed and, crucially, even with their eyes completely covered—and found measurable improvements in color contrast sensitivity 24 hours later 5.

• Vision improved significantly: Tritan (blue-yellow) contrast improved by ~16%, protan (red-green) by ~9%, and even with ocular coverage, a 7% tritan gain was observed, showing systemic effects.

• Clothing is no barrier: Ordinary garments transmitted infrared almost as effectively as bare skin.

What is the Mechanism? Mitochondrial Photobiomodulation

These results echo decades of photobiomodulation research. The authors found the following beneficial effects:

1. Cytochrome-c oxidase as a photoacceptor
   Near-infrared light (650–900 nm) is absorbed by cytochrome‑c oxidase in mitochondria, boosting ATP production.

2. Improved mitochondrial efficiency
   Low-intensity 830 nm red/invisible light applied to cells and tissues enhances ATP output and membrane potential while reducing pathogenic ROS.

3. Systemic (abscopal) effects
   Stimulating mitochondria in one area triggers systemic signaling (via cytokines or metabolic pathways) that benefits distant tissues—including the retina.

4. Vision-specific benefits
   Previous human trials using 670 nm red light directly on the eyes showed improved color contrast and ATP increase in aging photoreceptors 6.

5. Evolutionary context
   Humans evolved under full-spectrum sunlight (300–3000 nm). The deeper longer wavelengths penetrate tissue more effectively than visible light and may counteract mitochondrial aging.

Practical Takeaways

• Spend 15 min in natural sunlight daily, ideally close to midday when infrared output peaks.
• Keep clothes on—study shows infrared easily penetrates multiple layers.
• Eyes can remain covered, yet benefits to vision and mitochondrial health still occur.
• Consider room lighting with broader spectrum, or even infrared-emitting bulbs, to mimic sunlight indoors.
• Sunlight may help blood sugar control via systemic mitochondrial activation—evidence from 670 nm animal studies search6.

Conclusion

This new study confirms that infrared sunlight isn’t just skin-deep—it’s body-deep, triggering mitochondrial energizing responses that ripple through the system and sharpen vision—even without directly shining on the eyes. Combined with robust photobiomodulation literature, the evidence is clear: full-spectrum sunlight exposure is not optional—it’s essential to our biological roots.

Try this today: Step outside for 15 minutes, fully clothed, midday. No sunglasses. No gadgets. Just simple sunlight—and let your cells recharge.

References 

1. Jeffery G et al., Sci. Rep. 15, 24435 (2025)
2. Karu TI & Kolyakov SF, Photochem. Photobiol. (2004)
3. Eells JT et al., J. Biol. Chem. (2003) turn0search6
4. Shinhmar H, Hogg CR, Jeffery G., PLoS One (2023) citeturn0search0
5. Shinhmar H et al., Sci. Rep. (2021) turn0search11
6. Durieux J et al., Cell (2011) cite
7. Hart GB & Fitzgerald CE, J. Biophoton. (1979) cite
8. Tindale C., Biochim. Biophys. Acta (2022) turn0search10
9. FoundMyFitness review (2025) citeturn0search11
10. Nature Sci. Rep summary by Bruning K., PIE Magazine (2025
11. Holick, M. F. (2007). "Vitamin D deficiency." New England Journal of Medicine, 357(3), 266–281.
12. Deng, X., et al. (2018). "Magnesium, vitamin D status and mortality: results from US NHANES." The American Journal of Clinical Nutrition, 108(6), 1240–1246.
13. Cheng, S. F., et al. (2020). "Zinc and its influence on vitamin D metabolism." Nutrients, 12(4), 1230.
14. van Ballegooijen, A. J., et al. (2017). "The synergistic interplay between vitamins D and K for bone and cardiovascular health." Frontiers in Nutrition, 4, 6.
15. Zhang, Z., et al. (2006). "Vitamin A and D regulate calcium absorption." The Journal of Nutrition, 136(3), 877–882.
16. Nielsen, F. H. (2011). "Update on the relationship between boron and human health." Biological Trace Element Research, 144(1-3), 210–220.
17. Sakaguchi, Y., et al. (2018). "Magnesium modifies the association between vitamin D and mortality." Kidney International, 94(5), 960–969.