Vitamin D is a group of fat-soluble secosteroids responsible for increasing intestinal absorption of calcium, magnesium, and phosphate, and for many other biological effects.
The active form of vitamin D, calcitriol, is produced in the kidneys and circulates as a hormone, regulating the concentration of calcium and phosphate in the bloodstream.
Vitamin D is found in a small number of foods, including oily fish, red meat, liver, egg yolks, and fortified foods.
Vitamin D deficiency can result in impaired bone mineralization and bone damage, leading to bone-softening diseases such as rickets in children and osteomalacia in adults.