What is

vitamin D


Vitamin D is a fat soluble vitamin. It is formed in the skin when the skin is exposed to ultraviolet B rays in direct sunlight. Vitamin D is also available from plant sources and dairy products.

Which are the various

forms of vitamin D

available in diet or as supplements?

There are 2 supplement forms of vitamin D available. One of them is vitamin D2, also called as ergocalciferol. This form is synthesized from plants and yeast. It is used in very high dose for supplementation. The other form of supplement is vitamin D3, also called as cholecalciferol. This form is the most active form of vitamin D. Vitamin D2 and D3 are not active in the body. Both forms must be metabolized into an active form in the body called as calcitriol.

How is vitamin D formed in the body?
Vitamin D formed in the skin or eaten in the diet is carried in the bloodstream to the liver, where it is converted into the calcidiol (25 hydroxy vitamin D3). Circulating calcidiol is then converted into calcitriol (1,25 dihydroxy vitamin D3), the biologically active form of vitamin D, either in the kidneys or by immune cells.

What are the

functions of vitamin D


When active form of vitamin D3 is synthesized by immune system of the body, then vitamin D3 helps in defending the body against microbial invaders. Vitamin D deficiency has emerged as a clear risk factor for tuberculosis and leprosy.

When synthesized in the kidneys, calcitriol circulates as a hormone, regulating the concentration of calcium and phosphate in the bloodstream.

How is the calcium and phosphorus balance in the body maintained by vitamin D?
Effect of calcitriol on intestine, bone, kidney and parathyroid gland cells leads to the maintenance of calcium and phosphorus levels in the blood. It promotes absorption of calcium and phosphorus from the intestine and helps in deposition of these into the bones. Along with parathyroid hormone it thus helps to make the bones stronger.

Which are the common
food sources of vitamin D

The most common food source is fortified foods, mainly cereals and dairy products. Vitamin D3 is also present in fish liver oils and fatty fish. Human breast milk contains only small amounts of vitamin D.

What is the
daily requirement of vitamin D
in the human body?

Daily requirement of vitamin D is 5mcg/day or 200IU.

How common is deficiency of vitamin D?
Deficiency of Vitamin D is very common in Indian children. This is because of deficient Vitamin D in breast milk due to deficiency in mother?s milk and subsequently due to poor intake in food. The deficiency can also occur in the winter at northern and southern latitudes or in people who keep their bodies covered as skin production of vitamin D does not occur.

What happens in case of deficiency of vitamin D in the body?
Vitamin D deficiency leads to decrease blood calcium and phosphorus levels. This can lead to fits and seizures. To try to increase the low calcium level in blood caused by vitamin D deficiency, the parathyroid hormone level increases, which draws calcium out of bone to increase the calcium level in blood. Thus, bones are weakened. Patients may have muscle aches, weakness, and bone pain. Persistent deficiency of vitamin D can lead to rickets in children and osteomalacia in adults. This results in thin, brittle, or misshapen bones.

How to treat vitamin D deficiency?
Treatment of vitamin D deficiency consists of intake of food rich in vitamin D. Supplements in form of ergocalciferol or calciferol is given. Dose of these supplements depends on the severity of vitamin D deficiency.

With respect to women who are breastfeeding, the American Academy of Pediatrics (AAP) and the Canadian Pediatric Society (CPS) have both recommended vitamin D supplementation for both mothers and infants. The AAP has recommended 200 IU of vitamin D per day for all infants 2 months and older, and 400 IU for newborns during the first days of life. This direct supplementation for the infant is separate and apart from any vitamin D supplementation that the mother herself might need.

What happens in case of over dosage of vitamin D?
Taking very high daily doses of vitamin D can cause toxicity, high blood levels of calcium and deposition of calcium in the kidneys that can lead to kidney stones and even damage to the kidneys.