Vitamin D is not only a vitamin, it is actually a hormone. You probably have heard a lot of media buzz around its importance lately but you likely haven't been hearing is your doctor talking about it. I'm not entirely sure why that is - though I would have a few guesses...
The Vitamin D Council is an organization that compiles the latest research regarding this substance. If you are interested, it's a great idea to take a look at their information. For those who don't want to take the time, I'll give you an executive summary here:
Vitamin D deficiency is associated with things like autoimmune disease, cancer, heart disease, and depression. So you don't want to be low!
Vitamin D is made out of cholesterol in response to sunlight exposure in a healthy person. Sadly, many of us aren't able to make this complicated conversion from sunlight to hormone for a variety of reasons. When someone's total cholesterol is under 150, for example, (this most commonly can happen in people taking statin drugs) hormone synthesis is compromised. Also, insulin resistance and type 2 diabetes appear to create issues around this conversion as well.
You can get some Vitamin D from animal sources - but generally not nearly as much as one can get from sunlight. Since it is a fat soluble vitamin, it is found mainly in fatty animal foods - assuming the animal had plenty of exposure to sunlight...
So it would make sense for people to take Vitamin D. However, there is a potential toxicity problem. I always recommend all my clients get their Vitamin D levels tested. This is a quick and inexpensive blood test that I offer my clients or alternatively, your doctor will probably be happy to order it up for you if you ask. In fact, you can order it up for yourself at directlabs.com . In fact, it happens to be their March special for $39.
Your test comes back in a couple of days. If your numbers are low, you'll need to supplement with a source of D3 with a dosage determined by your health care professional.
In my opinion, keeping your Vitamin D levels in check might be one of the easiest and cheapest ways to cut down on your risk of cancer.