Don't play favorites with this pair. Invite them both to your supplement party.

When calcium and vitamin D get together, their powers multiply. Not only do they help build your bones and boost your immune system function, but, according to new research, they also help ward off type 2 diabetes. Research shows you'll be a whopping 33 percent less likely to develop the condition if you get at least 1,200 milligrams (mg) of calcium and 800 international units (IU) of vitamin D per day compared to an intake of only 600 mg of calcium and less than 400 IU of vitamin D daily.

Although it's best to get many nutrients from food, the study showed that getting vitamin D and calcium from supplements -- not dietary sources -- was associated with a lower diabetes risk. It's difficult to get enough vitamin D and calcium from food, anyway -- especially vitamin D -- so make sure your supplement includes both. It's particularly important during the shorter winter days when you may get little sunlight, which helps your body manufacture vitamin D.

The RealAge Optimum (RAO) dose of vitamin D is 400 IU per day for people under age 70 and 600 IU per day for people over age 70. But the upper intake level is 2,000 IU -- meaning anything up to that level is generally considered safe.