While preserving my usual skepticsm about what "studies say...", it does make sense that humans would need a good dose of full- body sunlight daily.
Recent studies say 40 mins/day (without sun block), or 20 minutes per side or until done to taste.
With unblocked sunlight over enough of your body, your skin produces the right sorts of Vit D that you need for full health, vigor, and maybe even cancer prevention. Roofers get enough but, in my experience, roofers often tend to destroy themselves with crystal meth and/or alcohol. It's a roofer thing.
The alternative is to do the research yourself and try to figure out what kind and what amounts of Vit D a person ought to take as pills. As I have posted here in the past, Vit D is the only vitamin I take on the advice of all of my doc friends. However, I also take my shirt off whenever I can.
Happiness is a state of undress: why it’s time to stop worrying and love the bikini ...
Dietary Supplement Fact Sheet: Vitamin D
(Men, middle-aged and above, also probably need a baby aspirin and Vitamin L - Lipitor, but don't take medical advice off the internet. Including mine.)