You may enjoy The Great Vitamin D Experiment thread. It been been going on a very long time, posts in recent years are many new studies on benefits of Vit D, not members trying the original protocol.
http://forum.lowcarber.org/showthread.php?t=396439
Here's a post from me Dec 2016, http://forum.lowcarber.org/showpost...&postcount=1644 my views on why I had low Vit D before and why eliminating processed seed oils corrected them is very much from the Paleo world.

Does he also mention that the older you are the harder it is for your skin to synthesize Vit D from the sun? That was a bummer, so even though I get a lot of sun, being ancient myself... I still supplement.

Thanks for the recommendation...Dr Ruscio's book was ordered by our library but some of these gut Books are a bit fringy, I’ll try it now. I agree about Moore's writing style, wish Dr Westman hadn’t agreed to advise on those books, but many people do like that more "readable" approach, and I do use the "optimal" numbers in the back of the Cholesterol book.