Vitamin B12 (also known as cobalamin) is an essential coenzyme of various metabolic reactions and a key factor for neuronal health and regeneration. Vitamin B12 cannot be synthesized by people and is an exclusive product of bacteria and archaea. Lack of proper nutritional uptake of B12 may lead to deficits that are reflected by fatigue, depressive symptoms, and cognitive deficits and in the end may lead to irreversible neuronal degeneration.
A very large epidemiological study (sample size 9670 participants) determined associations between low intake of vitamin B12 and depressive symptoms (Sanchez- Villegas et al. 2009). Interestingly, vitamin B12 deficiency was determined in almost a 50% of relatively young (mean age 39 years) military personnel with noise- induced hearing loss and tinnitus and only in 27% of personnel with noise-induced hearing loss without tinnitus (Attias et al. 2002; Shemesh et al. 1993). Some attempts to supplement B12 deficiency in tinnitus patients produced results, which were not convincing (Berkiten et al. 2013), but in other studies, the decrease in tinnitus- related distress was statistically significant (Singh et al. 2016). Nevertheless, vitamin B12 seems to be a biomarker worth looking at and should be acknowledged on the potential blood biomarkers for tinnitus.
Prestin is a transmembrane protein, expressed specifically by the outer auditory hair cells and responsible for their ability to move and therefore, to amplify the acoustic signal in the cochlea (Dallos 2008). During the noise exposure, some auditory hair cells are getting damaged and their proteins were proposed to get spilled to circulation. Prestin was suggested by Parham as a hypothetical serum biomarker indicating damage to the outer hair cells and predicting hearing loss as well as consequent tinnitus (Parham 2015). This hypothesis was supported by evidence obtained in animal model of noise-induced hearing loss (Parham and Dyhrfjeld-Johnsen 2016). It remains to be established how long does prestin circulate in blood following the acoustic injury and to what extend its presence would correlate with the presence of tinnitus percept and/or tinnitus-related distress.