The effects of 'supra-physiological' vitamin B12 administration on temporary threshold shift

The aim of this study was to evaluate, in 20 young volunteer subjects, the effects of supra-physiological vitamin B12 administration on noise-induced temporary threshold shift (TTS). All subjects had hearing thresholds within 15dB HL and type A tympanograms. The subjects were randomly assigned to two different groups. Experimental group subjects received cyanocobalamin, I mg daily for 7 days, and 5 mg on the eighth day. Control group subjects received a placebo injection daily for 8 days. The vitamin B 12 concentration, hearing thresholds and TTS2 (10min of exposure, narrowband noise centred at 3 kHz, band-width of 775 Hz, 112dB SPL) were mcasured before and 8 days after treatment. At the end of treatment, the serum vitamin B12 concentration was significantly increased in the experimental group. After 8 days of treatment, the control group showed the same hearing thresholds and TTS2 degrees. Statistical analysis showed that TTS2 decreased significantly at 3 and 4 kHz when cobalamin was used to increase the serum concentration of vitamin B 12 to >2350pg/ml. In addition, a protective effect at 3 kHz in the experimental group was evident when compared with the placebo group. These results suggest that elevated plasma cyanocobalamin levels may reduce the risk of hearing dysfunction resulting from noise exposure in healthy, young subjects.