The University Record, August 13, 1996

Excessive doses of vitamin B6 can be dangerous,
study shows

Doctors who prescribe large doses of vitamin B6 aren't doing their patients any good, and they might be causing harm, researchers found.


By Deborah Gilbert
News and Information Services

Carpal tunnel syndrome sufferers who take vitamin B6 in hopes of improving their condition are wasting their money and may be jeopardizing their health.

The largest and most comprehensive study to date of the relationship between vitamin B6 and carpal tunnel syndrome found no correlation between a patient's vitamin B6 status and the hand/wrist ailment.

The lead author of the study, Alfred Franzblau of the School of Public Health, also cautions that excessive doses of vitamin B6 are neurotoxic and can cause sensory nerve damage. According to the U.S. Bureau of Labor Statistics, there were 38,300 cases of carpal tunnel syndrome involving lost work days in 1994---up from 33,000 cases in 1992.

The study is reported in the May issue of the Journal of Occupational and Environmental Medicine.

"Unfortunately, a number of small studies and some anecdotal evidence have convinced many physicians to routinely prescribe supplementation with vitamin B6 as part of the clinical management of carpal tunnel syndrome," says Franzblau.

However, those studies were flawed, he notes, adding that they included "small samples of non-randomly selected subjects" and frequently relied on subjective measures of outcome.

The U-M study is the first to measure blood levels of vitamin B6 with two different laboratory tests, assess ulnar and median nerve function in the wrists and hands, and obtain carpal tunnel syndrome symptoms among a large sample---125 employees in two auto parts plants. Carpal tunnel syndrome symptoms include numbness, tingling, burning or pain in the wrists, hands or fingers.

The researchers found that 40 employees (32 percent) reported symptoms consistent with carpal tunnel syndrome, 31 employees (24.8 percent) had median nerve dysfunction as determined by nerve function tests, and 10 employees (8 percent) had a vitamin B6 deficiency. However, there was no relationship between the vitamin deficiency, symptoms of carpal tunnel syndrome or impaired nerve function.

"Our primary concern is that patients may be overdosing on vitamin B6 as prescribed by their physicians, some of whom are prescribing 300 milligrams a day or more," Franzblau says. "While most reported cases of sensory neuropathy related to vitamin B6 supplements involve dosages of more than 1,000 milligrams a day, some cases involve dosages as low as 200 milligrams a day. The United States Recommended Dietary Allowance for vitamin B6 for adults, incidentally, is just 1.6-2.0 milligrams a day."

Franzblau's colleagues on the study were Cheryl L. Rock, associate professor of human nutrition, School of Public Health; Robert A. Werner, School of Public Health, Veterans Administration Medical Center in Ann Arbor, and Department of Physical Medicine and Rehabilitation, Medical School; James W. Albers, School of Public Health and Department of Neurology, Medical School; and Matthew P. Kelly and Elizabeth C. Johnston, graduate students, School of Public Health.