Pharmacists are the go-to source to identify possible drug-micronutrient interactions and counsel patients on the benefits of B vitamins.
The B vitamins can be obtained through protein-rich foods such as fish, poultry, eggs, meat, and dairy products, as well as from leafy green vegetables and nuts. In addition, many cereals are fortified with B vitamins. A host of vitamin B supplements are also available on the market. To help patients understand which B vitamins are best for their needs, a brief explanation of the role played by each type is presented here.
Thiamine is involved in the metabolism of carbohydrates, fat, amino acids, glucose, and alcohol.2
It is also necessary for myocardial function and nerve cell function.3
In the United States, thiamine deficiency is found primarily in alcoholics.2
Because diuretics have been shown to increase the urinary excretion of thiamine, patients on chronic diuretic therapy may be at increased risk of subclinical thiamine deficiency and should discuss the need for supplementation with their primary health care provider.4
Riboflavin is essential for cellular growth and maintenance of vision, mucous membranes, skin, hair, and nails.4
Intake of riboflavin may result in a yellow-orange discoloration of the urine, so patients should be made aware of this effect. However, no significant drug interactions have been reported for this B vitamin, nor has a safe upper limit been determined.4,5
Niacin refers to both nicotinic acid and its derivatives, including nicotinamideadenine dinucleotide and nicotinamide adenine dinucleotide phosphate, which are coenzymes in oxidation–reduction reactions.6
All the derivatives of niacin are crucial in cell metabolism.6
Because dietary tryptophan can be metabolized to niacin, tryptophan-rich foods, such as dairy products, may be able to compensate for inadequate dietary niacin.6
Niacin toxicity may cause nausea, vomiting, diarrhea, hepatotoxicity, tachycardia, and hypertension.4
In therapeutic doses, niacin will lower triglycerides and low-density lipoprotein cholesterol by mechanisms unrelated to its function as an essential micronutrient.4
Niacin, but not niacinamide, is FDA approved for the adjunctive treatment of hyperlipidemia and hypercholesterolemia.4
The most common adverse effects associated with therapeutic doses of niacin are flushing and a sensation of warmth in the areas of the face, neck, and ears.4
In some cases, niacin may also impair liver function and cause glucose intolerance or hyperuricemia.4
Prior to using niacin supplements, patients should be sure to consult with their primary health care provider.
B5 (Pantothenic Acid)
Pantothenic acid is a precursor of coenzyme A, which is essential in many biologic reactions and plays a significant role in cholesterol, steroid, and fatty acid synthesis.4
No significant drug interactions are known to exist with this vitamin. However, doses of greater than 10 g per day have been known to cause diarrhea.7
Pyridoxine is required by the body for deriving energy from food, for producing red blood cells, and for the proper functioning of nerves. It is used to treat and prevent pyridoxine deficiency resulting from poor diet, certain medications, and some medical conditions. Pyridoxine has been used in the treatment of carpal tunnel syndrome, premenstrual syndrome, depression, and migraines. However, more clinical research is required regarding its effectiveness in treating these conditions. Doses should be limited to 100 mg per day due to the risk of peripheral neuropathy with higher doses.4
Biotin is required for various metabolic functions, including carbohydrate, fat, and amino acid metabolism.4
As a supplement, it is used to prevent and treat biotin deficiency associated with pregnancy, long-term tube feeding, malnutrition, and rapid weight loss.4,7
It is also used orally for hair loss, brittle nails, skin rash (seborrheic dermatitis) in infants, diabetes, and mild depression.8
There are no known drug interactions with biotin.8
Cyanocobalamin is active in all cells, especially those in the bone marrow, central nervous system, and the gastrointestinal tract.4
Along with folate (see below), cyanocobalamin is essential for DNA synthesis.4,9
Cyanocobalamin is necessary for the formation of blood cells, nerve sheaths, and various proteins, and it is used in the recycling of homocysteine and folate.9
It is also essential in the metabolism of fat, protein, and carbohydrates.4
Cyanocobalamin deficiencies can result in megaloblastic anemia, peripheral neuropathy, or dementia.9
Pharmacologic agents and conditions that can affect cyanocobalamin levels and affect lab tests include aspirin, oral contraceptives, metformin, proton pump inhibitors, H2 -receptor antagonists, and anticonvulsants, as well as smoking and multiple myeloma.9
Folate (Folic Acid)
Folate aids in the production and maintenance of new cells. It is especially important during periods of rapid cell division and growth such as during infancy and pregnancy.10
Folate is also essential to making DNA and RNA and helps prevent changes to DNA that may lead to cancer.10
Both adults and children require folate to make normal red blood cells and prevent anemia.4
Folate is also essential for the metabolism of homocysteine and helps maintain normal levels of this amino acid.4,10
Pharmacologic agents that may interact with folate use include anticonvulsants, metformin, sulfasalazine, and methotrexate.4,10
Folic acid, the synthetic form of folate, is approved by the FDA for use in the treatment of megaloblastic anemia caused by folate deficiency that is associated with tropical and nontropical sprue, nutritional anemias, pregnancy, infancy, and lactation.4
It is also approved for the prevention of neural tube defects in newborns.4
Recommendations for childbearing women include 400 mcg of folic acid per day.4,10
The B vitamins are available as singleentity supplements, but they are more commonly formulated together as vitamin B–complex supplements, which generally include high doses of all 8 B vitamins. However, some combination products do not contain all of these ingredients and some may include others, such as biotin, para-aminobenzoic acid, choline bitartrate, and inositol.2
B-complex supplements are available in tablet, capsule, liquid, and sublingual formulations. Prior to beginning to take B-complex supplements, patients should be encouraged to consult with their primary health care provider to determine whether doing so is appropriate, especially if the patient has preexisting medical conditions or is currently taking any other pharmacologic agents. Pharmacists are in a pivotal position to identify possible drug–micronutrient interactions and other possible contraindications to using B vitamin supplements. Patients should also be reminded that there is no substitute for eating a balanced nutritious diet to obtain the essential vitamins and minerals. For more information on the B vitamins, please visit the National Institutes of Health’s Office of Dietary Supplements website at http://ods.od.nih.gov/.
Ms. Terrie is a clinical pharmacy writer based in Haymarket, Virginia.
The B vitamins. Medline Plus website. www.nlm.nih.gov/medlineplus/bvitamins.html. Accessed July 31, 2012.
Thiamine. Medline Plus website. www.nlm.nih.gov/medlineplus/druginfo/natural/965.html#Description. Accessed July 31, 2012.
Thiamine. Merck Manual for Healthcare Professionals Online Edition. www.merckmanuals.com/professional/nutritional_disorders/vitamin_deficiency_dependency_and_toxicity/thiamin.html. Accessed July 31, 2012.
Huckleberry Y, Rollins C. Essential and conditionally essential nutrients. In Krinsky D, Berardi R, Ferreri S, et al, eds. Handbook of Nonprescription Drugs. 17th ed. Washington, DC: American Pharmacists Association; 2012.
Riboflavin. Medline Plus website. www.merckmanuals.com/home/print/disorders_of_nutrition/vitamins/riboflavin.html. Accessed July 31, 2012.
Niacin. Merck Manual for Healthcare Professionals Online Edition. www.merckmanuals.com/professional/nutritional_disorders/vitamin_deficiency_dependency_and_toxicity/niacin.html. Accessed July 31, 2012.
Pantothenic acid. Medscape website. http://reference.medscape.com/drug/vitamin-b5-pantothenic-acid-344423#7. Accessed July 31, 2012.
Biotin Medline Plus website. www.nlm.nih.gov/medlineplus/druginfo/natural/313.html. Accessed July 31, 2012.
Vitamin B12. Medscape website. http://emedicine.medscape.com/article/2086344-overview. Accessed July 31, 2012.
Folate. NIH Office of Dietary Supplements website. http://ods.od.nih.gov/factsheets/Folate-HealthProfessional/. Accessed July 31, 2012.