But what doses did they take in the research? Vitamin D RDA has been increased by like 5-10x recently in some countries (others are still lagging behind), becau

But what doses did they take in the research? Vitamin D RDA has been increased by like 5-10x recently in some countries (others are still lagging behind), because the RDA that we've used for decades had a calculation error. If the studies dosed vitamin D based on recommendations then it shouldn't be surprising that supplementing vitamin D didn't work. Considering that only a few countries have updated their vitamin D RDA in the past few years, and most haven't, then I think it's likely that most studies on the topic will have too low of a dose of vitamin D supplementation. The vitamin D error: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4210929/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4210929/ --- It's also possible that some of the health benefits don't come from vitamin D or UV exposure, but instead from something like red light exposure or some other wavelength. (Red) light therapy is a popular topic for example. It's mostly touted to improve skin aging and it's being studied as a help with myopia in children. Does it work? No idea.