This is very important because if your blood calcium levels are not within a normal range you are dead. Vitamin D can regulate the calcium levels by influencing the amount of calcium absorbed from the calcium passing through the digestive tract, causing calcium either to be deposited or withdrawn from bones and influencing the amount of calcium that is excreted through the kidneys. Vitamin D is fat soluble which means that it must be dissolved in fat to be carried into the body can be stored in fat in the body tissues, therefore does not have to be ingested every day and can easily build up to toxic levels is likely to be deficient in persons who eat an extremely low fat diet. If the calciferol is not adequate to raise the serum calcium level, the kidney converts the calciferol to the most active form, dihydroxy vitamin D. Amount needed is 400 I.U. or 10 micrograms. Since we live in a society that has us wearing clothing, taking baths, staying indoors, etc., vitamin D is added to milk.
Severe deficiencies are rickets in children and osteomalacia in adults.
For descriptions of these diseases read page 234 in your textbook. This can easily occur if supplements are given and vitamin enriched cereals are eaten in large quantity. Vitamin D is the most toxic of all the vitamins. Sources are exposure to sunlight, fish liver oils, fortified milk and margarine, and eggs. Absorption of vitamin D made on the surface of the skin takes 6 to 8 hours to be absorbed.