Solubility characteristics divide the vitamins into two major classes: the water-soluble vitamins and the fat-soluble vitamins.
There are nine water-soluble vitamins and four fat-soluble vitamins. The fat soluble vitamins A, D, E and K are chemically similar and found in fats and oils of food.
Fat soluble vitamins in general carried in the blood by protein carriers, are stored in fat tissues, are needed in periodic doses and are more likely to be toxic when consumed in excess of need.
These vitamins are absorbed like dietary fat – with the assistance of bile acids. Once absorbed, the fat soluble vitamins enter the lymphatic system before circulating in the blood.
They are transported through the blood by lipoprotein because they are not soluble in water.
Excess fat soluble vitamins are stored in the liver and adipose tissue and remain there until needed.
Fat soluble vitamins play diverse roles in the body.
Vitamins A and D may act somewhat like hormones, directing cells to convert one substance to another, to store this or to release that.
Other functions of vitamin A including maintenance of vision in dim light, maintenance of mucous membranes and healthy skin and involve in growth and development of bones.
Vitamin E flows throughout the body, preventing oxidative destruction of tissues. Vitamin E is considered essential for protection of cell structure, especially of red blood cells. Vitamin K is necessary for blood to clot.
Fat soluble vitamins
