Vitamin B6

Q:  I am 68-year old woman not taking any prescription drugs. I have trouble sleeping and recently purchased a product called Melatonex. Melatonex contains 10 mg of vitamin B6 or 500% RDA. The Centrum Silver I take daily contains 3 mg of B6 or 150% RDA - making a total of 13 mg daily. I've been told that excess B6 is harmlessly passed through the body. A recent Family Circle magazine article stated that an overdose of B6 can cause tingling, pain or numbness in the limbs, depression, headaches, fatigue and trouble walking. Who can I believe - how much is too much?

A:  Some people have the mistaken notion that just because something is "natural" or a vitamin that it is harmless to the body, even taken in mega-doses. Vitamin B6, also called pyridoxine, is one of the family of B vitamins that are important to the nervous system. It is found in many food sources (chicken, fish, eggs, spinach, potatoes, bananas, whole wheat bread) so most people get adequate amounts. The RDA (recommended daily allowance) is about 2 mg.

Until the mid-1980s we didn't realize that large amounts could be dangerous. I remember giving a lecture many years ago about PMS (premenstrual syndrome) and recommending 100 mg/d to alleviate some of the symptoms. Now we know that doses that high taken on a chronic basis can be toxic to nerves. B6 is a water-soluble vitamin, which means that most of it does pass out through your urine, but large doses over months will build up and damage nerve cells. A safe maximum has not been established, but I do not believe that your total of 13 mg per day will result in harm. That is still well below the 100 mg/day dosages that have been reported to cause trouble.

"Dear Doctor" is a compilation of patient questions answered by doctors from the Medical College of Wisconsin.