Vitamin D

Vitamin D is a small class of compounds known as calciferols. This vitamin is unique in that the human body can actually produce it on its own, using ultraviolet light from the sun to convert a derivative of cholesterol into a calciferol. Despite this, many people still require vitamin D from their diet, especially those who live in climates with long winters, where sunlight hours are short and the temperature may require clothing that prevents the absorption of sunlight. 

Vitamin D is heavily involved with calcium absorption byt the body, and is therefore associated with bone health. Vitamin D is also involved in cell differentiation, similar to vitamin A. Food sources of vitamin D are fewer in number than other vitamins, but fish and seafood, such as oysters, salmon, and catfish are reliable sources, as well as milk, although milk is usually fortified with extra vitamin D after processing.