In a three-year study, 728 older men and women with high blood homocysteine levels and no hearing loss were given either daily oral folic acid or a placebo supplement. Daily folic acid supplementation slowed decline in hearing of low frequencies by 0.7dB after three years.
Folic acid did not affect hearing thresholds of the high frequencies. However, the participants lived in the Netherlands, which at the time did not allow folic acid fortification of food, so participants’ baseline folate levels were about half those found in the U.S. population. Authors say, “Considering that the folate status of older adults is generally low in countries without folic acid fortification programs, our findings suggest a possible way to diminish the public health burden of hearing loss in those countries.”