<prompt> Which among the following is the richest source of vitamin D?MilkEggGreen leafy vegetablesFish oil  <response>: The main natural source of vitamin D in the diet is in the livers of fish, which ingest ultraviolet-irradiated sterols in phytoplankton and zooplankton and store the vitamin D produced in their livers. A major source of vitamin D is its synthesis in the skin upon ultraviolet B UV-B wavelength, 290-315 nm exposure. Except for fish, food unless foified contains only limited amounts of vitamin D. Vitamin D2 ergocalciferol is obtained from plant sources and is the chemical form found in some supplements. Ref: Shoback D.M., Sellmeyer D.E. 2010. Chapter 17. Disorders of the Parathyroids Calcium Phosphorus Metabolism. In McPhee S.J., Hammer G.D. Eds,Pathophysiology of Disease, 6e. 