In the paleo diet, there isn't a need for MUCH supplementation because we are supposed to get everything we need from the real food we eat. Of course, that doesn't always happen and everyone has different goals. I, for instance, take a generic multivitamin and a fish oil pill with breakfast and dinner. I ran this by my doctor along with the basics of the paleo diet, of which he was familiar, and said that I was doing everything perfectly. I also mentioned that I had taken some Vitamin D in the beginning and he began to warn me about oversupplementation with Vitamin D. Let's see why we need Vitamin D.
Vitamin D is produced by cholesterol in the skin when in contact with sunlight (UVB to be specific). This is why getting at least 15 minutes of direct sunlight every day is recommended. Mark Sisson says, "One thirty minute session of full-body (no shirt, shorts, no sunblock) sun exposure when the sun is at its strongest, for example, can get you between 10-20,000 IUs of endogenous vitamin D production. If you get 20,000 IU a week, you’re way ahead of the game." That's if you can get that much. The issue also comes in during the colder months and for those that work indoors all day. You may not get that kind of powerful sun exposure at all during a work week if you are in this scenario.