Here's a massive meta-analysis of tens of thousands of participants finding a reduction in mortality associated with vitamin D supplementation: https://www.coc

Here's a massive meta-analysis of tens of thousands of participants finding a reduction in mortality associated with vitamin D supplementation: https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD007470.pub3/full?highlightAbstract=mortality%7Cwithdrawn%7Cd%7Cvitamin%7Cmortal https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD... Vitamin D + calcium supplementation for bone health in middle-aged or older people: https://link.springer.com/article/10.1007/s00198-015-3386-5 https://link.springer.com/article/10.1007/s00198-015-3386-5 But you're right that some of the benefit of "vitamin D" will be associated with going outside. I outlined several reasons in my article: the outdoors has brighter lights, lower carbon dioxide, etc., which are good for our health.