This is probably one of the most authoritative source on whether Vit D is good for you [1]. I was never much of a believer, but this article prompted me to rei

This is probably one of the most authoritative source on whether Vit D is good for you [1]. I was never much of a believer, but this article prompted me to reinvestigate it, and I'm surprised to see that there is an effect if you're looking at elderly adult population. Also, as others have mentioned, there is such a thing as too much - taking too much can affect the balance of your other vitamin levels. There was a nice trial on beta-carotene which showed it increasing mortality which was very unexpected, but made sense once people understood the biochemical pathways better.[2] [1] http://onlinelibrary.wiley.com/doi/10.1002/14651858.CD007470.pub3/abstract http://onlinelibrary.wiley.com/doi/10.1002/14651858.CD007470... [2] https://www.ncbi.nlm.nih.gov/pubmed/20155614 https://www.ncbi.nlm.nih.gov/pubmed/20155614