The B-vitamin complex is a group of eight compounds. B-vitamins are all involved in cellular metabolism and energy production to varying extents, but they have their unique functions as well. All B-vitamins are water-soluble and excesses are often eliminated in the urine, which makes most of the B-group non-toxic even in large dosages. However, supplemental niacin and folic acid can cause symptoms in large doses, and long-term mega-dosing of pyridoxine can lead to toxicity.
The B-Complex
The B-complex consists of thiamin, riboflavin, niacin, pantothenic acid, pyridoxine, biotin, folic acid and cobalamin. The water-solubility of the group makes it very difficult for toxic levels to accumulate, but not impossible. According to "Nutrition and Diagnosis-Related Care," deficiency of various B-vitamins is much more common in the United States than overdose symptoms. B-vitamins are often found together in the same foods such as meats, dairy products, green leafy vegetables, legumes and nuts.
Niacin Overdose Symptoms
The recommended dietary intake for niacin ranges from 2 mg per day for infants less than 6 months old, to 17 mg per day for lactating females. Supplementing with niacin, or vitamin B-3, in single dosages of 100 mg or more often leads to a phenomenon called "niacin flushing." Flushing is caused by generalized vasodilation, or relaxation, of the small arteries beneath the skin, which leads to temporary redness, tingling, itching, mild burning and perspiration around the face, head and neck. Hot flashes and increased heart rate can also occur. To avoid niacin flushing, you can take niacinamide, a synthetic variety that doesn't have vasodilating properties. According to "Medical Nutrition and Disease," daily intake of 3,000 mg of niacinamide and 1,500 mg of niacin are associated with nausea, vomiting and symptoms of liver toxicity.
Folic Acid
High dosages of folic acid, or vitamin B-9, do not lead to overdose symptoms, but it can mask a deficiency of vitamin B-12. According to "Vitamins: Fundamental Aspects in Nutrition and Health," long-term doses of at least 3,000 micrograms daily of folic acid can mask vitamin B-12 deficiency, which can lead to symptoms similar to those of Alzheimer's disease and eventually permanent neurological damage. The recommended daily intake for folic acid ranges from 150 micrograms daily for infants less than 6 months old, to 600 micrograms for pregnant women. Taking folic acid supplements prior to and during pregnancy reduces the risks of neural tube defects in babies.
Pyridoxine Toxicity Signs
According to "Nutritional Sciences", toxicity from vitamin B-6 cannot occur from overindulging in natural dietary sources, but it can occur from supplementing with pyridoxine, which is a synthetic form. The recommended daily intake of pyridoxine for adults is 2 mg daily; signs and symptoms of toxicity are not thought to occur until dosages reach at least 100 mg per day, and perhaps as high as 500 mg, for many weeks or months, according to "Doctor's Complete Guide to Vitamins and Minerals." Early signs of toxicity are related to nerve irritation and include numbness and tingling in the extremities, headaches and muscle spasms. Advanced symptoms of toxicity include profound fatigue, mood disturbance, nerve damage, poor balance and coordination, and loss of muscle strength. People suffering from pyridoxine toxicity may take many months to recover once they stop supplementing, although some never fully recover.
References
- "Nutrition and Diagnosis-Related Care"; Sylvia Escott-Stump; 2008
- "The Vitamins, Third Edition"; Gerald F. Combs; 2007
- "Medical Nutrition and Disease: A Case-based Approach"; Lisa Hark; 2008
- "Vitamins: Fundamental Aspects in Nutrition and Health"; G. Combs; 2008
- "Nutritional Sciences"; Michelle McGuire; 2007
- "Doctor's Complete Guide to Vitamins and Minerals"; Mary Dan Eades and Philip Lief; 2002
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