The Full Spectrum Advantage: Why Sunlight Does What Vitamin D Alone Cannot

TL;DR:  Sunlight—especially its infrared and red wavelengths—boosts mitochondrial energy and cellular resilience in ways vitamin D supplements can’t match. Vitamin D is still essential, but pills only fix deficiency; they don’t deliver full-spectrum light benefits. The optimal strategy is safe, non‑burning daily sun exposure plus monitored vitamin D levels for comprehensive metabolic and immune support.

Dr. Roger Seheult, a board‑certified critical care, pulmonary, sleep, and internal medicine physician (and founder of MedCram), maintains that sunlight provides effects the body cannot fully replicate with vitamin D supplements. His view focuses on the non–vitamin D components of sunlight—particularly near‑infrared (NIR) and red light—which penetrate deeply (several centimeters into tissue, sometimes even through clothing), enhance mitochondrial function, boost ATP production, reduce oxidative stress through local mitochondrial melatonin, and improve cellular energy efficiency. These effects operate independently of, and extend beyond, the vitamin D pathway targeted by oral supplements.

Here is a summary of Seheult’s claims with substantial scientific grounding:

• Infrared/NIR light improves mitochondrial efficiency (supported by Glen Jeffery’s work and related photobiomodulation studies).^[5,6]
• Observational data (Swedish ~30,000-woman cohort; UK Biobank analyses) link greater sun exposure to lower all-cause, cardiovascular, and non-skin-cancer mortality.  
• Clinical signals include shorter hospital stays near windows, faster recovery in a small Brazilian randomized trial using a 940 nm infrared LED vest on COVID patients, and measurable improvements in retinal color contrast sensitivity from brief 670 nm red-light exposure.  
• Vitamin D levels largely act as a marker of prior sun exposure; supplementation alone has not fully matched the recovery or systemic benefits seen with actual light in the cited observations.

This leads naturally to a complementary point: while sunlight’s non–vitamin D wavelengths exert unique mitochondrial effects, vitamin D itself carries its own well‑established health associations.

Well‑established findings on the health benefits of vitamin D add complementary but distinct points:

• Vitamin D deficiency or insufficiency remains common, and higher serum levels (often >30–50 ng/mL / 75–125 nmol/L, depending on the outcome) are associated—based on observational studies and narrative‑review evidence—with better results for cardiovascular disease, certain cancers, type 2 diabetes, hypertension, COVID severity, and all‑cause mortality.
• One perspective (Grant et al. 2022 narrative review) and an Israeli pre-infection study support targeting levels above conventional sufficiency cutoffs for broader benefits, while also highlighting innate immune modulation.  
• However, large RCTs have shown more limited effects when participants start near average levels, and mainstream guidelines still treat ≥20–30 ng/mL as sufficient for most people, with higher targets remaining investigational.

Beyond Vitamin D: The Full Spectrum Case for Smart Sun Exposure

Taken together, the evidence supports a clear synthesis: sunlight’s full spectrum—especially its infrared and red wavelengths—delivers physiological effects that vitamin D supplements cannot replicate, while maintaining adequate vitamin D status remains an independent and essential health goal. Sunlight provides both the photobiomodulation benefits Seheult emphasizes and the natural production of vitamin D, whereas supplementation serves as a reliable backup when outdoor exposure is limited. The two strategies complement each other rather than compete. Caveats still matter. UV exposure carries well‑documented risks of skin aging and cancer, so the practical target is non‑burning, moderate exposure, often cited as roughly 15–20 minutes of relevant wavelengths for mitochondrial effects. Observational findings can be influenced by confounding, and neither extreme sun avoidance nor high‑dose, unsupervised supplementation is ideal. Individual factors—skin type, latitude, age, baseline vitamin D levels, and medical conditions—shape the optimal approach, making testing and professional guidance advisable.

Key Health Takeaways  

• Infrared/red light effects—Sunlight’s infrared and red wavelengths penetrate deeply and enhance mitochondrial ATP production, reduce oxidative stress, and support cellular energy in ways oral vitamin D cannot.
• Moderate daily outdoor exposure—Regular non‑burning light exposure to skin and eyes is linked to better recovery markers, lower mortality in large cohorts, and specific benefits such as improved retinal color‑contrast sensitivity.
• Vitamin D remains essential—Deficiency is common, and serum levels of at least 30 ng/mL (75 nmol/L)—with possible higher targets (40–50+ ng/mL) for certain outcomes—are supported by observational evidence for cardiovascular, metabolic, immune, and some cancer‑related associations.
• Supplements fill gaps —Pills effectively raise 25(OH)D and correct deficiency but do not replace the broader photobiomodulation effects of natural light.
• Practical approach —Prioritize safe, regular sun exposure when feasible, monitor vitamin D status medically, and balance benefits against UV risks.

In short, Seheult’s statement aligns with accumulated evidence: sunlight provides unique physiological actions beyond what vitamin D supplements can achieve, while adequate—and in some cases higher—vitamin D levels contribute their own distinct health advantages.

Further Inspiration & Resources

1. Heiskanen, V., Pfiffner, M., & Partonen, T. (2020). Sunlight and health: Shifting the focus from vitamin D3 to photobiomodulation by red and near-infrared light. Ageing Research Reviews, 61, 101089. 
• Directly argues that associations between sun exposure and better health outcomes are better explained by red/NIR photobiomodulation than by vitamin D alone, noting the failure of many vitamin D supplementation trials.
2. Hamblin, M. R. (2018). Mechanisms and mitochondrial redox signaling in photobiomodulation. Photochemistry and Photobiology, 94(2), 199–212. 
• Reviews how red and near-infrared light are absorbed by cytochrome c oxidase in mitochondria, dissociating nitric oxide, increasing ATP production, and triggering beneficial redox signaling — mechanisms independent of vitamin D.
3. Arranz-Paraíso, D., Sola, Y., Baeza-Moyano, D., Benítez-Martínez, M., Melero-Tur, S., & González-Lezcano, R. A. (2023). Mitochondria and light: An overview of the pathways triggered in skin and retina with incident infrared radiation. Journal of Photochemistry and Photobiology B: Biology, 238, 112614. 
• Examines infrared radiation’s effects on mitochondrial pathways in skin and retina, including ATP stimulation and cellular improvements that go beyond vitamin D.
4. Riedmann, U., et al. (2025). Beneficial health effects of ultraviolet radiation: Expert review and conference report. Photochemical & Photobiological Sciences, 24(6), 867–893. 
• Expert review emphasizing health benefits of UVR/sunlight that extend far beyond vitamin D synthesis, including nitric oxide release, blood-pressure lowering, and neuro-immune-endocrine pathways.
5. Shinhmar, H., Grewal, M., Sivaprasad, S., Hogg, C., Chong, V., Neveu, M., & Jeffery, G. (2020). Optically improved mitochondrial function redeems aged human visual decline. The Journals of Gerontology: Series A, Biological Sciences and Medical Sciences, 75(9), e49–e52. 
6. Shinhmar, H., Hogg, C., Neveu, M., & Jeffery, G. (2021). Weeklong improved colour contrasts sensitivity after single 670 nm exposures associated with enhanced mitochondrial function. Scientific Reports, 11(1), Article 22872.