Zinc supplementation for tinnitus.
Level 1 - systematic review of randomized trials
Systematic review of randomized controlled trials
PubMed 27879981 · doi:10.1002/14651858.CD009832.pub2
What was done
This Cochrane systematic review searched major databases through July 2016 for randomized controlled trials comparing oral zinc supplementation to placebo in adults with subjective tinnitus. Primary outcomes included improvement in tinnitus severity/disability measured by validated questionnaires and adverse effects. Secondary outcomes included tinnitus loudness, subjective severity scales, quality of life, and pure tone audiometry thresholds. Outcome certainty was evaluated using GRADE.
What was found
Three trials totaling 209 participants were included. In the only study using a validated instrument (Tinnitus Handicap Questionnaire in 109 elderly patients), there was no significant difference in improvement at four months: 5% (5/93) in the zinc group versus 2% (2/94) in the placebo group (risk ratio 2.53, 95% CI 0.50 to 12.70; very low-quality evidence). Tinnitus loudness showed no significant difference at eight weeks (mean difference -9.71 dB, 95% CI -25.53 to 6.11) or at four months on a 0–100 scale (mean difference 0.50, 95% CI -5.08 to 6.08). Non-validated severity scores also showed no significant effect at eight weeks (mean difference -1.41 on a 0–7 scale, 95% CI -2.97 to 0.15; and response rate RR 1.09, 95% CI 0.17 to 7.10). No significant adverse effects were reported. None of the studies measured quality of life, psychoacoustic parameters, or audiometry thresholds.
Why it matters
Despite biological plausibility regarding zinc's role in cochlear function, current randomized evidence does not support using oral zinc supplementation to relieve tinnitus symptoms.
Limits
The total sample size was small (three trials, 209 participants), and all studies had moderate to high risk of bias. Heterogeneity in patient criteria, follow-up duration, and outcome tools prevented meta-analysis. Only one trial used a validated assessment tool, and all evidence was graded as very low certainty.