Vitamin D
Overview
Vitamin D is a group of fat-soluble secosteroids responsible for increasing intestinal absorption of calcium, magnesium, and phosphate, and multiple other biological effects. In humans, the most important compounds in this group are vitamin D3 (also known as cholecalciferol) and vitamin D2 (ergocalciferol).
Biochemistry
Vitamin D is unique because it can be made in the skin from exposure to sunlight. Vitamin D exists in two forms. Vitamin D2 is obtained from the UV irradiation of the yeast sterol ergosterol and is found naturally in sun-exposed mushrooms. Humans and other animals can synthesize vitamin D3 from 7-dehydrocholesterol, a compound found in the skin that absorbs UVB light.
Function
Vitamin D increases the efficiency of the intestinal absorption of calcium and phosphate. This effect is vital for the body's homeostasis mechanisms, such as bone cell and muscle function. Vitamin D is also involved in the immune system and other processes such as cell growth, neuromuscular function, and inflammation.
Deficiency
Deficiency can result in impaired bone mineralization and bone damage, which leads to bone-softening diseases, including rickets in children and osteomalacia in adults.
Sources
The body can produce vitamin D in response to sunlight. It can also be obtained from dietary sources and supplements. Foods that contain vitamin D include fatty fish, beef liver, cheese, and egg yolks.
Daily Requirements
The Recommended Dietary Allowance (RDA) for vitamin D varies depending on age, sex, and life stage. The RDA is set to meet the needs of almost all (97–98%) individuals in a group.
Health Effects
Vitamin D has a significant role in calcium homeostasis and metabolism. Its discovery was due to effort to find the dietary substance lacking in children with rickets. Beyond its use to prevent osteomalacia or rickets, the evidence for other health effects of vitamin D supplementation in the general population is inconsistent.