Vitamin D: Why You Need It, Where to Get It and How Much

Vitamins are substances the body needs to grow and develop normally. Vitamin D matters because it helps the body absorb calcium, one of the main building blocks of bone. Too little vitamin D can lead to bone diseases such as osteoporosis or rickets.

It also plays a part in the nerves, muscles and immune system:

• muscles need it to move;
• nerves need it to carry messages between the brain and the body;
• the immune system needs it to fight off bacteria and viruses.

Where vitamin D comes from

There are three ways to get it.

Sunlight. The body makes vitamin D naturally after the skin is exposed to sunlight. But too much sun can age the skin and cause skin cancer, so many people look to other sources.

Food. Very few foods contain vitamin D naturally — among them egg yolks, saltwater fish and liver. Most people get theirs from fortified foods, which have vitamin D added, such as milk, cereal and yogurt.

Supplements. Vitamin D comes on its own and in many multivitamins, in two forms, D2 and D3. Both raise the level of vitamin D in the blood, but D3 may raise it higher and for longer. Because vitamin D is fat-soluble, it is absorbed better when taken with a meal or snack that contains some fat.

How much you need

The amount depends on age. Recommended daily amounts, in international units (IU):

Who may need extra

• Older adults.
• Breastfed infants.
• People with dark skin.
• People with conditions that limit how the body absorbs fat, such as Crohn's disease, celiac disease and ulcerative colitis.
• People who have obesity or have had gastric bypass surgery.

Ask your health care provider whether you need a vitamin D supplement and, if so, how much. They may first want to test your vitamin D level to see whether you are getting enough.

Sources

• MedlinePlus, U.S. National Library of Medicine, "Vitamin D," drawing on the NIH Office of Dietary Supplements. https://medlineplus.gov/vitamind.html
• Rewritten in hubnx's own words.