Supplementation of 800 micrograms of folic acid daily as in ActiFolate by Metagenics is helpful. In one study that took place over three years, subjects who received placebo instead of folic acid experienced significantly greater loss of low frequency hearing. Men over the age of 60 who reported the highest intake of folate and/or folic acid were significantly less likely to develop hearing loss.
Intake of ActiFolate (1 tab) or Multigenics (6 tabs) will provide folate; folic acid is the supplement form of folate. Beta carotene, vitamins C and E are all useful as well.
You can get more folate in your diet by eating spinach and other leafy green vegetables, asparagus, peas, beans, chickpeas, and liver.