Full-Spectrum Sunlight Deficiency as a Plausible Substantial Contributor to Non-Communicable Diseases

This paper proposes that full-spectrum sunlight deficiency is a plausible and substantial contributor to the global epidemic of non-communicable diseases. It argues that sunlight acts through five independent biological pathways: near-infrared stimulation of mitochondrial cytochrome c oxidase (the primary pathway), UVB-driven vitamin D synthesis, UVA-mediated nitric oxide release, visible-light retinal dopamine signaling, and circadian photoentrainment. The multi-pathway model explains a persistent anomaly in the literature—strong observational associations between greater sun exposure and lower mortality that are not reproduced by vitamin D supplementation trials. The paper incorporates recent evidence (including UK Biobank sensor data and Mendelian randomization results), evaluates the hypothesis within a Bayesian framework, and identifies the definitive test still needed: a full-spectrum phototherapy randomized controlled trial.