Vitamins play a vital role in many biochemical functions in the human body and are essential components for maintaining optimal health. There are two main groups of vitamins – those that are fat soluble (easily stored in fat upon absorption) and those that are water soluble (washed out and not easily stored). Although adequate intake of all vitamins is important, due to the transient nature of water-soluble vitamins, regular intake is required to avoid deficiency. The water-soluble vitamins include Vitamin C and Vitamin B complex (thiamine, riboflavin, niacin, pantothenic acid, pyridoxine, biotin, folate, and cobalamin).
Vitamin B complex and vitamin C are found in many foods, especially vegetables and fruits, as well as dairy, meat, legumes, peas, liver, eggs, and fortified grains and cereals. In addition to serving as cofactors in biochemical reactions, vitamin B complex is vital for normal body growth and development, healthy skin, properly functioning of nerves and the heart, and red blood cell formation. The overall lack of water-soluble vitamins is rare in North America, though it can present in alcoholism, malabsorption syndromes, strict veganism, and malnourished states.
As stated above, the deficiency of water-soluble vitamins is rare in North America. However, deficiency may be a presenting feature in alcoholism, malnourishment, and malabsorption syndromes such as short-bowel syndrome. In short-bowel syndrome, there is the removal of a large portion of the small intestine for various reasons such as Crohn disease, necrotizing enterocolitis, traumatic injury, obstruction, or cancer. The small bowel is the site of absorption for all vitamins, and if a significant portion gets surgically removed (typically enough so that less than or equal to 200 cm of bowel remains), the body will be unable to absorb vitamins adequately. Treatment includes vitamin supplementation.
Although it is tempting to simply obtain urine or serum levels of water-soluble vitamins, these reflect only presently circulating vitamin levels and are unable to approximate storage levels. Alternate forms of testing include immunoassays, chromatographic methods, chemical methods, high-pressure liquid chromatography, and capillary electrophoresis, depending on the vitamin being tested. For vitamin B12 (cyanocobalamin) and folate deficiency, as discussed below, it is essential to obtain a complete blood cell count (checking MCV, hematocrit, and hemoglobin) in addition to methylmalonic acid and homocysteine levels.
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