A hormone that plays a key role in ensuring the absorption of calcium from the intestines.

A vitamin that includes both CHOLECALCIFEROLS and ERGOCALCIFEROLS, which have the common effect of preventing or curing RICKETS in animals. It can also be viewed as a hormone since it can be formed in SKIN by action of ULTRAVIOLET RAYS upon the precursors, 7-dehydrocholesterol and ERGOSTEROL, and acts on VITAMIN D RECEPTORS to regulate CALCIUM in opposition to PARATHYROID HORMONE.

Vitamins are substances that your body needs to grow and develop normally. Vitamin D is important to your body because: It helps your body absorb calcium. Calcium is one of the main building blocks of bone. A lack of vitamin D can lead to bone diseases such as osteoporosis or rickets.; It also has a role in your nerve, muscle, and immune systems: Your muscles need it to move; Your nerves need it to carry messages between your brain and your body; Your immune system needs vitamin D to fight off bacteria and viruses. . You can get vitamin D in three ways: through your skin, from your diet, and from supplements. Your body forms vitamin D naturally after exposure to sunlight. However, too much sun exposure can lead to skin aging and skin cancer. So many people try to get their vitamin D from other sources. Very few foods naturally contain vitamin D. Most people get vitamin D in their diet from foods that are fortified. This means that vitamin D is added to the food. These foods may include milk, cereal, and yogurt. Foods that naturally have vitamin D include egg yolks, saltwater fish, and liver. Vitamin D is available in supplements. It is also included in many multivitamins. The two forms of vitamin D in supplements are D2 and D3. Both types increase vitamin D in your blood, but D3 might raise it higher and for longer than D2. Vitamin D is fat soluble. You can absorb it better when you take your supplements with a meal or snack that includes some fat. The amount of vitamin D you need each day depends on your age. The recommended amounts, in international units (IU), are: Birth to 12 months: 400 IU; Children 1-13 years: 600 IU; Teens 14-18 years: 600 IU; Adults 19-70 years: 600 IU; Adults 71 years and older: 800 IU; People who are pregnant or breastfeeding: 600 IU. But certain people may need extra vitamin D, such as: Older adults; Breastfed infants; People with dark skin; People with certain conditions that limit the absorption of fat, such as Crohn's disease, celiac disease, and ulcerative colitis; People who have obesity or have had gastric bypass surgery. Check with your health care provider to see if you need to take vitamin D supplements, and if so, how much you should take. Your provider may want to first do a vitamin D test to see if you are getting enough of it. NIH: National Institutes of Health Office of Dietary Supplements