show that two patients who took 500 mg/day of pyridoxine for 8 and 36 months developed sensory neuropathy and as did one patient who took 100 to 200 mg/day for 36 months. This finding conflicts with the weight of evidence showing that daily doses in the range of 100 to 200 mg are not associated with the development of this condition. It is not clear from the report whether the neurological symptoms of the patient taking 100 to 200 mg/day were confirmed by a clinical neurological examination. The report notes that clinical neurological examinations were performed on about half of the patients. In addition, the report notes that electrophysiological studies were performed on seven patients and sural nerve biopsies were performed on two patients. It is not clear from the report which patients were examined clinically and which received additional tests. A local television report publicizing this syndrome before the study may have biased the selection of patients and reporting of neurological symptoms.
Two additional studies that report sensory neuropathy at doses of less than 200 mg/day (Dalton, 1985; Dalton and Dalton, 1987) warrant examination. In a letter to the editor, Dalton (1985) reported sensory neuropathy (characterized as burning, shooting, and tingling pains; paresthesia of limbs; clumsiness, ataxia; or perioral numbness) in 23 of 58 women (40 percent) being treated with 50 to 300 mg/day of pyridoxine for premenstrual syndrome. This case report contains methodological flaws including lack of information on the duration of treatment, use of other medications or herbal preparations, and lack of confirmatory information on actual doses consumed.
In a subsequent publication, which may have included patients from the earlier case report (Dalton, 1985), Dalton and Dalton (1987) retrospectively studied 172 women who were attending a private practice specializing in premenstrual syndrome and who were reported to have taken 50 to 500 mg/day of pyridoxine. The subjects were divided into two groups: 103 women who complained of neurological symptoms and 69 who did not. Neurological symptoms were not adequately detailed in this study. In addition, the actual doses may be underestimated because the patients were also taking vitamin supplements. In summary, the weaknesses of this study and the inconsistency of the results with the weight of evidence pertaining to the safety of higher doses of pyridoxine rule out the use of these data to determine a UL.