Vitamin D Supplement

I was sitting in the Doctor's office the other day, being seen by a PA, so I asked him what type of supplement he thought was the best on the market (making small talk). He told me hands down that everyone should be on a D3 supplement and that it would help with weight regulation, mood and pretty much anything else positive in the world. I began doing some reading on vitamin D. Any experience or knowledge out there?

Vitamin D Supplement