Vitamins, Water-Soluble Health Article

Pantothenic Acid (Vitamin B5)

Pantothenic acid is stable in moist heat. It is destroyed by vinegar (acid), baking soda (alkali), and dry heat. Significant losses occur during the processing and refining of foods. Pantothenic acid is released from coenzyme A in food in the small intestine. After absorption, it is transported to tissues, where coenzyme A is resynthesized. Coenzyme A is essential for the formation of energy as adenosine triphosphate (ATP) from carbohydrate, protein, alcohol, and fat. Coenzyme A is also important in the synthesis of fatty acids, cholesterol, steroids, and the neurotransmitter acetylcholine, which is essential for transmission of nerve impulses to muscles.

Dietary deficiency occurs in conjunction with other B-vitamin deficiencies. In studies, experimentally induced deficiency in humans has resulted in headache, fatigue, impaired muscle coordination, abdominal cramps, and vomiting.

Biotin (Vitamin B8)

Biotin is the most stable of B vitamins. It is commonly found in two forms: the free vitamin and the protein-bound coenzyme form called biocytin. Biotin is absorbed in the small intestine, and it requires digestion by enzyme biotinidase, which is present in the small intestine. Biotin is synthesized by bacteria in the large intestine, but its absorption is questionable. Biotincontaining coenzymes participate in key reactions that produce energy from carbohydrate and synthesize fatty acids and protein.

Avidin is a protein in raw egg white, which can bind to the biotin in the stomach and decrease its absorption. Therefore, consumption of raw whites is of concern due to the risk of becoming biotin deficient. Cooking the egg white, however, destroys avidin. Deficiency may develop in infants born with a genetic defect that results in reduced levels of biotinidase. In the past, biotin deficiency was observed in infants fed biotin-deficient formula, so it is now added to infant formulas and other baby foods.

Vitamin B6

Vitamin B₆ is present in three forms: pyridoxal, pyridoxine, and pyridoxamine. All forms can be converted to the active vitamin-B₆ coenzyme in the body. Pyridoxal phosphate (PLP) is the predominant biologically active form. Vitamin B₆ is not stable in heat or in alkaline conditions, so cooking and food processing reduce its content in food. Both coenzyme and free forms are absorbed in the small intestine and transported to the liver, where they are phosphorylated and released into circulation, bound to albumin for transport to tissues. Vitamin B₆ is stored in the muscle and only excreted in urine when intake is excessive.

PLP participates in amino acid synthesis and the interconversion of some amino acids. It catalyzes a step in the synthesis of hemoglobin, which is needed to transport oxygen in blood. PLP helps maintain blood glucose levels by facilitating the release of glucose from liver and muscle glycogen. It also plays a role in the synthesis of many neurotransmitters important for brain function. This has led some physicians to prescribe megadoses of B₆ to patients with psychological problems such as depression and mood swings, and to some women for premenstrual syndrome (PMS). It is unclear, however, whether this therapy is effective. PLP participates in the conversion of the amino acid tryptophan to niacin and helps avoid niacin deficiency. Pyridoxine affects immune function, as it is essential for the formation of a type of white blood cell.

Populations at risk of vitamin-B₆ deficiency include alcoholics and elderly persons who consume an inadequate diet. Individuals taking medication to treat Parkinson's disease or tuberculosis may take extra vitamin B₆ with physician supervision. Carpal tunnel syndrome, a nerve disorder of the wrist, has also been treated with large daily doses of B₆. However, data on its effectiveness are conflicting.

Folic Acid, Folate, Folacin (Vitamin B9)

Folacin or folate, as it is usually called, is the form of vitamin B₉ naturally present in foods, whereas folic acid is the synthetic form added to fortified foods and supplements. Both forms are absorbed in the small intestine and stored in the liver. The folic acid form, however, is more efficiently absorbed and available to the body. When consumed in excess of needs, both forms are excreted in urine and easily destroyed by heat, oxidation, and light.

All forms of this vitamin are readily converted to the coenzyme form called tetrahydrofolate (THFA), which plays a key role in transferring single-carbon methyl units during the synthesis of DNA and RNA, and in interconversions of amino acids. Folate also plays an important role in the synthesis of neurotransmitters. Meeting folate needs can improve mood and mental functions.

Folate deficiency is one of the most common vitamin deficiencies. Early symptoms are nonspecific and include tiredness, irritability, and loss of appetite. Severe folate deficiency leads to macrocytic anemia, a condition in which cells in the bone marrow cannot divide normally and red blood cells remain in a large immature form called macrocytes. Large immature cells also appear along the length of the gastrointestinal tract, resulting in abdominal pain and diarrhea.

Pregnancy is a time of rapid cell multiplication and DNA synthesis, which increases the need for folate. Folate deficiency may lead to neural tube defects such as spina bifida (failure of the spine to close properly during the first month of pregnancy) and anencephaly (closure of the neural tube during fetal development, resulting in part of the cranium not being formed). Seventy percent of these defects could be avoided by adequate folate status before conception, and it is recommended that all women of childbearing age consume at least 400 micrograms (μg) of folic acid each day from fortified foods and supplements. Other groups at risk of deficiency include elderly persons and persons suffering from alcohol abuse or taking certain prescription drugs.