The B vitamins are a diverse group of nutrients that are commonly found together in foods. They are all water soluble, which means dietary excesses are usually easily eliminated in your urine. Most of the B vitamins are not stored well in your body, so you need to get them from your diet on a regular basis. Relatively large amounts of individual B vitamins are usually well tolerated, but one B vitamin – pyridoxine – can cause tingling when taken in high doses for prolonged periods. Ask your doctor about the best doses of B vitamins for you.
In general, the B vitamins serve as cofactors for enzymes that catalyze energy production in your body. B vitamins participate in converting carbohydrates to glucose, which is your cells' principal source of fuel, and they are instrumental in the metabolism of amino acids, proteins and fats. The B vitamins help keep your skin, hair, mucous membranes, liver, gastrointestinal tract and eyes healthy, and several B vitamins are essential for proper nervous system function. However, too much pyridoxine, or vitamin B6, has been associated with nerve damage.
According to Dr. Elson Haas, director of the Preventive Medical Center of Marin in San Rafael, Calif., pyridoxine can cause peripheral neuritis when taken in large doses – over 2,000 milligrams daily – for prolonged periods of time. Peripheral neuritis is characterized by tingling, loss of vibratory sensation and weakness in your hands and feet. It is usually reversible upon discontinuation of high-dose pyridoxine, but recovery can be slow, and in some people tingling and other sensory deficits are persistent.
Pyridoxine is required for normal nervous system function, and pyridoxine deficiency leads to a peripheral neuropathy that produces symptoms similar to the neuritis caused by pyridoxine toxicity. While pyridoxine is well-tolerated at doses up to 200 milligrams daily, at higher doses your body cannot easily convert pyridoxine to its biologically active form, pyridoxal phosphate. This results in accumulation of pyridoxine in your bloodstream and tissues. According to a study published in the June 2008 issue of "Journal of Veterinary Medicine," excess pyridoxine damages sensory nerves and injures sensory ganglia, or nerve centers, in your spinal cord.
Most B vitamins do not cause nerve damage, even at high doses. However, pyridoxine has been associated with a characteristic peripheral neuritis that usually occurs with prolonged intake of high doses, usually between 2 and 5 grams daily. Recommended dietary allowances for vitamin B6 – the amounts needed to prevent deficiency – vary from 100 micrograms daily for infants to 2 milligrams for nursing mothers. Due to pyridoxine's potential for causing nervous system injury, in 1998 the Institute of Medicine established a tolerable upper limit for vitamin B6 at 100 milligrams daily. Your physician or a nutritionist can help determine if you need additional B vitamins.
- “Staying Healthy with Nutrition – The Complete Guided to Diet and Nutritional Medicine: Vitamin B6 (Pyridoxine)”; Elson M. Haas, M.D.; 2006
- “The Merck Manual of Diagnosis and Therapy, 18th Edition: Vitamin B6 Toxicity”; Mark H. Beers, M.D., Editor-in-Chief; 2006
- “Journal of Veterinary Science”; Pyridoxine Induced Neuropathy by Subcutaneous Administration in Dogs; J. Chung, et al.; June 2008