Properties And Biological Importance Of Vitamin D

Elmer McCollum demonstrated the first existence of vitamin D in 1922. Due to its effects in treating rickets disease caused by rats, vitamin D is also called an antirachitic factor. As the human body synthesizes this vitamin when exposed to sunlight, it is called the sunshine vitamin as well. 

Characteristics of Vit D

• Vitamin D exists in various forms, of which Vitamin D2 and Vitamin D3 are the important ones. 
• They are called ergocalciferol and cholecalciferol respectively. 
• Cod liver oil is the best natural source of vitamin D. 
• Egg yolk, dairy products, and some fruits and vegetables also contain this vitamin but in smaller amounts. 
• Vit D2 has a plant origin while Vit D3 originated from animals. 

Structure and Properties of Vit D

• Vitamin D2 is produced from ergosterol in plants by its irradiation by ultraviolet light. 
• Vit D3 is produced from 7-dehydrocholesterol in animals through a similar process. 
• The molecule has a steroidal structure with four rings.
• The main structural difference between the D3 and D2 versions is the presence of a double bond in the D2 molecule, existing between the carbon atoms 22-23. It also has a methyl group in C24. 
• Vit D is an odourless, white crystalline, fat-soluble substance. 
• It is heat resistant and oxidation resistant and is also not affected by alkalis or acids. 

Metabolism of Vitamin D

Under the UVB light, 7-dehydrocholesterol in the epidermis of humans undergo a chemical reaction to initially form pre-vitamin D3. This is a non-enzymatic reaction. This will further make internal changes in the molecule to give rise to Vit D3.

• Vitamin D3 thus formed is transported to other parts of the body with the help of VDBP  binding. 
• Only one-half of the produced vitamin is transported to the liver where further processing happens until it is transformed into its circulating form. 
• The other half is stored in the adi[ose tissues. This will be stored for up to 2 months. 
• In the liver, Vit D is converted into its useful form of 25OHD3, with the help of a cytochrome. 
• The conversion of the circulating form of Vit D into its active form takes place in the kidneys. 
• In the kidney tubules, the 25OHD3 molecules undergo 1-alpha hydroxylation to form 1,25 (OH) 2D3 with an additional OH group in the first carbon of A ring. 
• The 23-hydroxylase enzymes in the inner membrane of mitochondria in kidney cells perform a stepwise reaction to convert the active form of Vit D3 into an inactive calcitroic acid.    

Biological Importance of Vit D

• The primary role of vitamin D is to help the body absorb, retain, and utilize calcium and phosphorus. Both of these are necessary to build bone structure. 
• Studies have also shown that it can help reduce inflammation, prevent cancer cell growth, and control infections. 
• Deficiency of this vitamin leads to health issues in the bones, inflammations, lower immunity, and rickets disease.

Additional Reading

• Classification of Vitamins With Examples
• Properties And Biological Role Of Vitamin A
• Properties and Biological Importance of Vitamin B
• Properties And Biological Importance Of Vitamin C