How Vitamins Are Digested

Vitamins are organic compounds found in small amounts in food. They are a type of essential micronutrient, meaning that the body requires only a small amount of each to function properly. Even so, without this small amount, physical signs and symptoms of deficiency can occur. Vitamins are not synthesized by the body and must therefore be obtained from food. The method of digestion and absorption of each nutrient depends on the type of vitamin it is: fat-soluble or water-soluble.

Fat-Soluble Vitamins

Vitamins A, D, E and K compose the fat-soluble vitamins. The absorption of all four of these nutrients is dependent upon the presence of dietary fat and adequately functioning biliary and pancreatic systems. Before vitamin A can be absorbed, the proteins bound to it must be removed by proteases in the stomach and small intestines. At this point, vitamin A is ready to go through the same absorption process as the other fat-soluble vitamins, via passive diffusion in the intestines.

B Vitamins

The B vitamins include thiamine, or B1, riboflavin, or B2, niacin, or B3, pantothenic acid, or B6, biotin, folic acid and vitamin B12, all of which are water-soluble. Most of the B vitamins are absorbed in a similar manner, through active, passive or facilitated diffusion in the small intestines. B12 is the only B vitamin that is absorbed differently. B12 is bound to protein in food. Upon entering the stomach, B12 is separated from the protein by acid in the stomach. It then moves to the small intestine and binds with a protein called intrinsic factor, which facilitates absorption into the blood stream.

Vitamin C

Also known as ascorbic acid, vitamin C is synthesized by plants and most animals from the sugars glucose and galactose. Unfortunately, humans are not capable of this, making it an essential water-soluble vitamin. Vitamin C is transported in the plasma in the form of ascorbic acid, which is then taken into the cells through either a glucose transporter using passive diffusion or an active transport system.

Vitamin Deficiency

If you don't get adequate amounts of the essential vitamins, because of poor nutrition or a malfunction in the absorptive process, symptoms will develop. Vitamin A deficiency can cause blindness and hair-follicle blockage. Deficiency in vitamin D causes bone to soften, which is the defining factor of rickets and osteomalacia. Thiamine deficiency produces the group of symptoms that characterize beriberi: confusion, muscle wasting, edema, peripheral neuropathy, tachycardia and an enlarged heart. Pellagra is the term given to severe niacin deficiency; symptoms include diarrhea, dermatitis and dementia. Deficiency in any vitamin will produce unwanted symptoms, which, unless the disease state is too advanced, can be reversed through the administration of the missing vitamin.