Longer wavelengths in sunlight pass through the human body and have a systemic impact which improves vision

#1

https://www.nature.com/articles/s41598-025-09785-3

Abstract

Long wavelength red light that can extend beyond the human visual range penetrates deeply through biological tissue. Exposure to these longer wavelengths improves mitochondrial function and ATP production. This can translate to improved physiological performance, particularly in the CNS, including the visual system. Light driven metabolic improvements to regional exposure can impact systemically. Here we show that infrared wavelengths from sunlight can be measured after they pass through the human thorax. We then select a prominent transmitted solar wavelength range (830–860 nm) and deliver this to the thorax of subjects in the lab in controlled 15 min exposures with and without ocular involvement. Clothing reduced wavelength intensity but was not a barrier. These exposures were associated with significantly improved visual function when measured 24 h later even in subjects in which light was blocked from the eyes. Our data show that longer wavelengths of sunlight penetrate through the human body and, consistent with animal studies, have the ability to improve function. While infrared light has been used on targeted tissues, its ability to improve distal tissues in humans has not been explored. This study also highlights the potentially important therapeutic value of sunlight whose longer wavelengths can reach key organs even through clothing and likely promote mitochondrial function counteracting the decline with age and disease.

O3 summary critique

Quick take — what the authors claim

  • Near‑infra‑red sunlight (≈800‑870 nm) can be detected after it traverses the human thorax, confirming that some solar energy literally “shines through” us. (Nature)
  • A 15‑min back‑only exposure to an 850 nm LED panel (9 mW cm⁝²) improved colour‑contrast sensitivity 24 h later—by ≈16 % on the tritan axis and ≈9 % on the protan axis—with smaller yet significant gains when the head/eyes were completely light‑shielded. (Nature)
  • Ordinary layered clothing was almost 100 × more transparent at 850 nm than in the visible range, suggesting daily sunlight could deliver a “mitochondrial boost” even through clothes. (Nature)
  • The authors argue that the effect is mediated by mitochondrial up‑regulation and raise public‑health alarms about modern white‑LED lighting, which lacks these longer wavelengths. (Nature)

In a nutshell (study design & findings)

Aspect Details
Participants 40 healthy Caucasian adults (25–63 y). Sub‑groups: 7 for sunlight measurements, 13 for 850 nm exposure, 5 “body‑only” (head wrapped in foil), 7 sham controls. (Nature, Nature)
Interventions (i) Field measurement of solar transmission through chest; (ii) Lab exposure to a ceiling‑mounted 850 nm LED panel aimed at the back for 15 min.
Primary outcome Psychophysical colour‑contrast thresholds (ChromaTest) 24 h post‑exposure.
Key results Tritan threshold ↓ 16 % (p = 0.0003) and protan ↓ 9 % (p = 0.005) after unshielded exposure; still significant (tritan ↓ 7 %) when ocular routes were blocked. (Nature)
Mechanistic observations Peak body transmission at 830–860 nm; clothing offers little resistance at these wavelengths. (Nature, Nature)

Strengths

  1. Novel empirical demonstration of deep‑tissue solar NIR transmission in living humans—previous work was post‑mortem or animal‑based.
  2. Within‑subject baseline comparison reduces inter‑individual variability for the vision metric.
  3. Attempted ocular shielding clarifies that at least part of the benefit is mediated systemically, not by stray retinal exposure.

Limitations & points to question

Category Critique
Sample & power Sub‑groups as small as n = 5–7 leave the study under‑powered, vulnerable to Type I/II errors, and hamper generalisability.
Blinding & expectancy Participants could feel heat from the active panel; experimenters were un‑blinded. A true double‑blind, sham‑heated LED would be needed to exclude placebo or practice effects in psychophysical testing.
Outcome choice Colour‑contrast thresholds are sensitive but also prone to learning effects—especially with a 24 h interval and repeated trials. No counter‑balanced control for test–retest improvement.
Duration of effect Only a single 24‑h follow‑up; sustainability beyond one day is unknown.
Mechanistic leap The link to mitochondrial ATP production is inferred from prior literature—no biochemical assays (e.g., retinal ATP, cytokines, glucose) were taken here.
Clothing claim Transparency images are qualitative; no spectroradiometric quantification or replication across fabrics.
Public‑health extrapolation Warnings about indoor white LEDs lack direct evidence from this dataset; they ignore exposure dose, spectrum variability, and real‑world behaviour.

How convincing is the evidence?

  • Internal validity: Moderate at best. The effect size is intriguing, but small samples and limited controls temper confidence.
  • External validity: Low. Healthy, mostly middle‑aged Caucasians in a lab setting; unclear relevance for older adults with retinal disease or diverse skin pigmentation.
  • Mechanistic plausibility: Supported by previous 670 nm data, yet still speculative without direct metabolic measurements here.

What would strengthen the case?

  1. Large, randomised, double‑blind trial comparing multiple NIR wavelengths, with sham‑heated controls to match tactile cues.
  2. Objective retinal/visual endpoints (ERG, OCT‑angiography) alongside psychophysics.
  3. Biochemical readouts (ATP, cytokines, glucose) to trace the systemic pathway.
  4. Dose–response and durability studies (minutes vs hours of exposure; follow‑up out to weeks).
  5. Quantitative fabric attenuation curves to validate the “through clothes” argument.
  6. Diverse cohorts (ageing, diabetic retinopathy, varied skin types) to test real‑world applicability.

Bottom line

The paper provides a provocative proof‑of‑concept that sunlight‑like near‑infra‑red can permeate the body and modestly enhance colour‑vision metrics without direct ocular exposure. The idea is biologically plausible and aligns with earlier photobiomodulation work, but the current evidence is preliminary—hampered by small samples, potential bias, and untested mechanistic assumptions. Treat these findings as an intriguing starting point rather than a clinical recommendation to skip sun‑block or retrofit office lighting.

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