What is Vitamin D3 1.0 mio.I.U./g kosher?

Vitamin D3 is both a vitamin and a hormone. It acts as a vitamin when it binds with calcium for proper absorption. Humans cannot digest calcium without adequate amounts of Vitamin D3.
Vitamin D is a group of fat-soluble secosteroids. In humans, vitamin D is unique both because it functions as a prohormone and because the body can synthesize it (as vitamin D3) when sun exposure is adequate.
Vitamin D3 is found in many dietary sources, such as fish, eggs, fortified milk, and cod liver oil. The sun also contributes significantly to the daily production of vitamin D, and as little as 10 minutes of exposure is thought to be enough to prevent deficiencies. The term "vitamin D" refers to several different forms of this vitamin. Two forms are important in humans: ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3). Vitamin D2 is synthesized by plants. Vitamin D3 is synthesized by humans in the skin when it is exposed to ultraviolet B (UVB) rays from sunlight. Foods may be fortified with vitamin D2 or D3.
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