There are a ton of RCTs showing that vitamin D supplementation prevents respiratory infections: https://www.google.com/search?q=vitamin+d+respiratory+infection&

There are a ton of RCTs showing that vitamin D supplementation prevents respiratory infections: https://www.google.com/search?q=vitamin+d+respiratory+infection&oq=vitamin+d+&aqs=chrome.2.69i57j0j69i59j0l2j69i60l2j69i61.5564j0j1&sourceid=chrome&ie=UTF-8 https://www.google.com/search?q=vitamin+d+respiratory+infect...