Vitamin D deficiency — when the level of vitamin D in your body is too low — can cause your bones to become thin, brittle or misshapen.

Vitamin D also appears to play a role in insulin production and immune function — and how this relates to chronic disease prevention and cancer — but this is still being investigated.

Although the amount of vitamin D adults get from their diets is often less than what's recommended, exposure to sunlight can make up for the difference. For most adults, vitamin D deficiency is not a concern. However, some groups — particularly people who are obese, who have dark skin and who are older than age 65 — may have lower levels of vitamin D due to their diets, little sun exposure or other factors.

The Recommended Dietary Allowance (RDA) for adults is 600 international units (IU) of vitamin D a day. That goes up to 800 IU a day for those older than age 70. To meet this level, choose foods that are rich in vitamin D. For example, choose fatty fish, such as salmon, trout, tuna and halibut, which offer higher amounts of vitamin D, or fortified foods, such as milk and yogurt.

Don't overdo it, though. Very high levels of vitamin D have not been shown to provide greater benefits. In fact, too much vitamin D has been linked to other health problems.

If you're concerned about whether you're getting enough vitamin D, talk to your doctor about your diet and whether a vitamin supplement might benefit you.