Our evidence library — what light does to the human body, graded by how well we actually know it.
Most writing about sunlight picks a side. One camp treats the sun as a carcinogen to be blocked;
the other treats it as a cure-all. Both flatten a literature that ranges from settled textbook
biology to single mouse studies — and the flattening is the problem, because the interesting
answers live in the gradations.
So we did the reading and kept the gradations. This library is where OPSIN shows its work:
the research the app's models rest on, the arguments the field has not settled, and an honest
grade on every claim.
Educational, not medical. OPSIN is a general wellness and lifestyle tracker,
not a medical device. Nothing here is a diagnosis, a treatment, or a dose recommendation for you
specifically — for that, talk to a clinician and get a blood test. See our
Medical Disclaimer.
Our deep-research review, and the foundation of everything else here — roughly 19,000 words
across sixteen sections, every substantive claim cited and graded. It covers:
Vitamin D as a hormone, not a vitamin — a receptor wired into ~3% of the human genome,
and why the "vitamin" framing set the doses too low.
The level debate — how the 600 IU RDA came to contain a ~10× statistical error, why the
Endocrine Society abandoned targets entirely in 2024, and why your blood test isn't what your cells see.
Forms, kinetics, and the safety ceiling — D2 vs D3 vs calcifediol, why your level moves
slowly, and where "more" stops helping.
Light beyond vitamin D — UVA and blood pressure, UV-induced immune tolerance, and the
red/near-infrared half of sunlight that acts directly on mitochondria.
Opsins and the body clock — melanopsin, the 71% melatonin suppression from ordinary
evening room light, and light sensors turning up outside the eye.
The condition map — falls, infections, cancer, diabetes, dementia, depression, IBD,
chronic pain, pregnancy, myopia — each with its evidence grade, including the null results.
Pills vs. sunshine — what VITAL and D2d really showed, and the structural reasons
supplement trials keep underselling sunlight.
What we still don't know — the open questions, and the citations we're still improving.
Read the review →· ~19,000 words · figures and reference tables · updated 30 July 2026
How we grade evidence
Every claim in the review carries one of four tiers, so you can tell trial-proven fact from
promising mechanism from expert belief:
Tier
What it means
A — Established
Randomized trials or meta-analyses of trials show the effect, or the mechanism is textbook biology
B — Strong but not proven
Consistent observational or genetic evidence, no definitive trial
C — Preliminary or mixed
Small, single-lineage, or conflicting human data
E — Expert position
A named researcher's stated belief that runs ahead of the trials — kept strictly separate
We also flag weak sources rather than hiding them. Citations labelled
secondary source rest on a general-audience summary instead of a primary paper, and
citations from organisations with a position in the debate are marked as such. The review's
closing section lists the citations we know need improving.
The practical version. How much sun you need for vitamin D, morning sunlight and
sleep, and why the winter sun stops working — a few minutes each instead of ninety.
The engine itself — the UV Index, the erythemal burn model, the vitamin D action
spectrum and its synthesis plateau, and the assumptions behind every number the app shows you.
This is where the science above becomes arithmetic.
Want this applied to your day and place? OPSIN turns the research above into a live
plan — the best windows to go outside today, how long is safe for your skin, and your vitamin D
balance sheet with an estimated blood level you can calibrate against a real test.
Launch the web app →