Vitamin D

Vitamin D is a group of fat-soluble steroids responsible for increasing intestinal absorption of calcium, magnesium, and phosphate, and many other biological effects. In humans, the most important compounds in this group are vitamin D3 (cholecalciferol) and vitamin D2 (ergocalciferol) 

Sources 

• Good sources of vitamin D include fatty fish, fish liver oils, egg yolk etc. 
• Milk is not a good source of vitamin D

Deficiency. 

• Vitamin D deficiency is relatively less common, since this vitamin can be synthesized in the body. However, insufficient exposure to sunlight and consumption of diet lacking vitamin D results in its deficiency. 
• Deficiency of vitamin D causes rickets in children and osteomalacia in adults. 
• Rickets is derived from an old English word 'wrickken', meaning to twist. 
• Osteomalacia is derived from Greek (osteon-bone; malakia-softness). Vitamin D is often called as antirachitic vitamin.