Erythrocyte folate, serum vitamin B12 and hearing loss in the 2003–2004 National Health And Nutrition Examination Survey (NHANES)

BACKGROUND/OBJECTIVE: Studies based on food frequency questionnaires suggest that folate and vitamin B12 intake could protect against hearing loss. We investigated whether erythrocyte folate and serum vitamin B12 levels are independently associated with hearing loss in humans. METHODS: Participants in the 2003–2004 US National Health and Nutrition Examination Survey who had data on hearing, folate, and vitamin B12 levels were included. Pure-tone average (PTA) at 0.5, 1.0, 2.0 and 4.0 kHz was computed for each ear. We used weighted logistic regression to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for the relation between quartiles of folate and vitamin B12, and hearing loss (present if PTA >25 dB in either ear and absent if PTA ≤25 dB in both ears). RESULTS: Participants (n=1,149) were 20 to 69 (mean 42) years old and 16.4% had hearing loss in at least one ear. Our data suggest a U-shaped relationship between folate and hearing loss. Compared to the 1(st) quartile, the ORs (95% CIs) for hearing loss were 0.87 (0.49–1.53), 0.70 (0.49–1.00) and 1.08 (0.61–1.94) for the 2(nd), 3(rd) and 4(th) quartile of erythrocyte folate in analyses adjusted for age, sex, vitamin B12, smoking, alcohol use, body mass index, race/ethnicity, exposure to noise, income and education. Although we observed inverse associations between vitamin B12 and hearing loss, the associations were not statistically significant (P>0.05). CONCLUSION: Our data show a U-shaped relationship between erythrocyte folate levels and hearing loss, suggesting a need to evaluate whether optimizing blood folate levels could prevent hearing loss.