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Is this more vitamin D evidence or is there something more going on?

Did you (and those who so far responded to you) actually read the article? The Vitamin D question is addressed throughout, e.g. "Linear regression models were fitted for the UV exposures and vitamin D serum levels, adjusted for the same confounders for each UV exposure described above, plus vitamin D supplementation."

> measured serum vitamin D levels, a biomarker for UV exposure,

That's entirely the opposite of adjusting the results for vitamin D levels. It's biasing the results by vitamin D levels.

The paper addresses this briefly, and suggests additional mechanisms to do with UV effects on different skin layers (e.g. NO mediated vasodilatation) may be involved.

I was under the impression that recent consensus was that Vitamin D supplementation has much less positive health impact than sunlight exposure?

Of course, there exists the whole field of photobiomodulation. Red light therapy (630/670/810/830/850/1060 nm red and NIR light) helps the eye in the morning (see Prof Glen Jeffery's work at UCL; the mitochondria are only sensitive to RLT during a certain window of the circadian rhythm, that coincides with early morning sunlight that is shifted towards the red/NIR), particularly when it comes to preventing and slowing age-related macular degeneration, but also improving colour perception, controlling blood glucose levels, improving athletic performance and recovery, mood and cognitive performance, and some other benefits. When I first got interested I thought I'd just get a small handheld LED device, but as I got deeper into it I decided to buy a large mains powered full body panel with 5 wavelengths. In particular the benefits to my sleep and skin have been fantastic, with the caveat that I live in northern Europe at a latitude of 53.3 degrees north. Perhaps those nearer the equator will feel more muted responses. That being said, improvements to vision are counterintuitively very difficult to actually judge without measuring, because the brain is constantly adjusting/hiding our defects.

Hi, do you happen to have to have some resources for someone interested in using red light therapy? Or even just a simple buying tip to get started. As someone with quite high myopia and a little bit of astigmatism thrown in, I'm at higher risk of myopic macular degeneration, so red light therapy might be extra useful!

I'm only seeing this now, sorry. First I'm not a doctor, so I can't give medical advice, certainly not if you believe you are already predisposed to something. I would say that there is no difference between the cheap and expensive devices, as long as they emit the correct wavelengths at the correct intensities. Since that's very low for targeting the eye (you are not trying to treat deeper joints/full body), you won't have to overspend. I think Prof Glen Jeffery mentioned a handheld red light in the 30 euro range for the morning treatment.

You can also look at (670/810 nm LED light strips to hang above your computer monitors and passively absorb some while starting at your monitor all day if you are getting an excess of blue light). I think that is another protocol though, but it might help.

I am sure though that it's more about consistency and treatment time (as in, you can't double the intensity to halve the treatment time). Furthermore, more is not better, it's more like an on/off switch after 2-3 minutes. You can do it every day, just like the solar spectrum is relatively higher in the required part of the spectrum at early morning sunrise every day.

But honestly, listen to Glen Jeffery, perhaps read /r/redlighttherapy

That is absolutely the right question to ask. If the results are not adjusted for vitamin D levels, and it does not appear that they are, then the results are largely useless because vitamin D is very easy to supplement.

Note: Adjusting by vitamin D levels is not the same as adjusting by supplemental intake. Even adjusting for supplemental intake must be a linear adjustment, not a binary one.

That's an overly simplistic approach.

Vitamin d supplementation studies are a lot more ambiguous than this though. And this also matches my "feel". Getting sun makes me feel good in a way that vitamin D supplementation never does. I was once at a dinner and sitting at the table with the head of the Office of Dietary Supplements for the US government and asked him this question- "How should I get vitamin D and how much should I take?" He answered quite quickly "Get it from sunlight." Your skin autoregulates how much vitamin D is made this way.

"The health effects of vitamin D supplementation: evidence from human studies"

https://www.nature.com/articles/s41574-021-00593-z

I do think the question is complicated by the fact that humans have wildly different skin tones. What is applicable for skin types that are very pale is quite different than darker skin tones. This question has been complicated even more by recent migration of humans into zones their skin was never meant to be exposed to. It feels like the dermatologists all made their guidelines based on people with porcelain skin that live at the equator. The truth is more complicated than that, people with darker skin develop low vitamin D status follwing those guidelines. Humans love to have blanket rules they can follow without regard to extenuating circumstances like different skin tones, but that isn't reality.

> "Get it from sunlight."

Listening to such people in power is a path to getting yourself killed, in this case by diseases. Their interest is in preserving their power, first by taking it away from you.

They always have to say "don't supplement" because asking everyday people to supplement will force the officials to admit that the food and/or environment has recently been made inadequate. This will put the officials in a corner that they cannot get out of.

The study you linked is defective by design. It uses a threshold of 50 nmol/l which is a pathetically low 20 ng/ml. Such studies are engineered to show a null result.

There are specific medical conditions that respond well to uv exposure (perhaps through mechanisms like apoptosis and changes to the immune system) that don't benefit much from vitamin D supplementation. I would be wary about assuming those benefits can be generalized or outweigh the known risks of uv exposure. People who spend more time outdoors likely have more physically active lives, are less exposed to VOCs and infections and there could be many demographic differences that are hard to control.

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