B-complex consists of eight vitamers that all play important roles in cellular metabolism, among other functions. Vitamers are compounds that have similar and related function, but different molecular structure. Folic acid, or vitamin B-9, is a B-complex member and is required for cell division and growth, especially within developing embryos. Most B-vitamins are excreted out of the body quickly when in excess, although some are stored for longer periods and some cause side effects in large doses. Folic acid is not known to cause side effects in large dosages, but it can mask a vitamin B-12 deficiency.
About Folic Acid
In addition to its role in metabolism and energy production, folic acid is needed to synthesize and repair DNA, which is vital during the early rapid growth and development of embryos. A lack of folic acid increases the risk of neural tube defects, which include malformations of the spine, skull and brain, according to "Human Biochemistry and Disease." Folic acid also contributes to the manufacture of red blood cells and helps to eliminate homocysteine from the blood, which is associated with higher incidence of atherosclerosis. The National Institutes of Health recommends that adults consume at least 400 micrograms of folic acid per day, although that is increased to 600 micrograms for pregnant women.
Folic Acid Side Effects
Most B-complex supplements do not contain more than the daily recommended dose of 400 micrograms of folic acid. Much larger doses do not lead to overdose side effects, but it can mask a deficiency of vitamin B-12 because the two vitamins share similar functions. It is estimated that long-term doses of 3,000 micrograms of folic acid per day is enough to mask an underlying B-12 deficiency, which can lead to neurological damage and symptoms very similar to those of Alzheimer's disease, as cited in "Vitamins: Fundamental Aspects in Nutrition and Health."
Niacin Side Effects
Niacin, or vitamin B-3, can cause side effects in large doses. The recommended daily allowance ranges from 2 mg in infants under 6 months old to 17 mg for lactating females, although some B-complex supplements contain 100 mg of niacin. Taking niacin in doses of 100 mg or more at a time can lead to "niacin flushing," which is caused by sudden vasodilation or relaxation of small blood vessels underneath the skin, according to "Biochemical, Physiological and Molecular Aspects of Human Nutrition." Niacin flushing is a temporary and usually harmless condition experienced as redness, sweating, tingling, itching and mild burning around the head and neck. To avoid niacin flushing, most makers of B-complex supplements use niacinimide that doesn't have vasodilating properties.
Pyridoxine Side Effects
Pyridoxine, or vitamin B-6, is the only B-vitamin that can cause serious side effects in large doses over long periods of time. B-6 is needed to maintain healthy nerves, but too much of it can have toxic effects on the nervous system. The recommended dietary allowance of B-6 for adults is 2 mg daily, but some B-complex supplements contain up to 100 mg. Toxic side effects related to B-6 overdose are not thought to occur until doses reach at least 100 mg per day, but perhaps as high as 500 mg daily, for many weeks or months consecutively, according to "Harrison's Principles of Internal Medicine." Early signs of toxicity include numbness and tingling in the arms and legs, headaches and muscle twitching.
References
- "Human Biochemistry and Disease"; Gerald Litwack; 2008
- National Institutes of Health: Office of Dietary Supplements: Folate
- "Vitamins: Fundamental Aspects in Nutrition and Health"; G. Combs; 2008
- "Biochemical, Physiological and Molecular Aspects of Human Nutrition"; Martha Stipanuk; 2006
- "Harrison's Principles of Internal Medicine"; A. Fauci et al.; 2008
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