Nearly everyone knows that vitamin D helps build strong bones. But it has plenty of other uses, too, and some are incredibly important for your health. Nearly all your cells have receptors (that is, docking ports) for vitamin D, meaning that it influences pretty much everything that happens in your body.

“A large number of people are deficient or marginal in vitamin D levels, and a majority are suboptimal,” says nutritionally oriented physician Michael Janson, MD, of New Smyrna Beach, Florida. “Deficiencies are related to heart disease, cancer, inflammatory conditions, bone disorders and numerous other health problems.”

Of course, you can make your own vitamin D, presuming you’re not afraid to spend 10 to 15 minutes in the sun daily without sunscreen on your arms and legs. But unless you live in the extreme-southern United States, the winter sun is too low for you to make much vitamin D. And on top of that, if you’re overweight, your vitamin D gets locked up in fat cells and remains largely unavailable for the rest of your body.

That makes supplementation paramount. Vitamin D3, also known as cholecalciferol, is processed from either sheep lanolin or lichen. Vitamin D2, also called ergocalciferol, comes from fungi. Our bodies absorb vitamin D3 twice as well as they do vitamin D2.

Here's the very latest in vitamin D research.