Axons are usually surrounded by a fatty substance called myelin. Myelin allows action potentials to propagate quickly from one neuron to another, allowing for rapid signal transmission. It is a critical part of the nervous system and it's absence has devastating effects, as seen in conditions such as multiple sclerosis.
Researchers have found that patients with low levels of folate in their blood are more likely to develop hearing loss (Gok 2004; Lasisi 2010; Gopinath 2010), and that low vitamin B12 levels are associated with hearing loss (Gok 2004) and tinnitus (Shemesh 1993).
Dietary supplementation with vitamins that have antioxidant capabilities can help protect the hair cells of the cochlea. One animal study showed that a 35-day pretreatment regimen of vitamin C may be able to protect against noise-induced hearing loss (McFadden 2005). Similarly, supplementing animals with certain forms of vitamins A and E have shown significant protective effects (Hou 2003; Ahn 2005).