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Many elderly folks with hearing issues assume it is a normal part of aging; this type of loss is even termed “age-related hearing loss. According to a National Institute on Deafness estimate, 33% of those over 65 have significant hearing impairment. There are two types of hearing loss, conductive and sensorineural. Conductive loss results from eardrum defects or problems with the tiny bones between the ear drum and the cochlea, often coming from injury of some sort. Sensorineural hearing loss (SNHL) is the most common type. Traditionally it is ascribed to nerve damage to the tiny hair cells in the cochlea followed eventually by loss in the auditory nerves leading from the ear to the brain. Recently, studies suggest there may be a more complicated explanation.
Research published in 2017 by M. Charles Liberman at the Department of Otolaryngology, Harvard Medical School, looking at noise-induced and age-related hearing loss called attention to the way that temporary noise exposure could lead to “reversible threshold shifts (and no hair cell loss) nevertheless cause permanent loss of >50% of the synaptic connections between hair cells and the auditory nerve.” This can result in a “hidden hearing loss.” Similarly, with age-related hearing loss, it appears that the connections between cochlear nerves (synapses) and the brain come before loss of hair cells and elevations in hearing thresholds. These losses, because of where they occurred were noted only in environments with a lot of noise, not in quiet situations. The actual neurons involved between the ear and brain could take years for complete degeneration even though the synaptic link between neurons and hair cells were damaged.
Liberman identifies a specific problem with this finding and hearing tests, writing:
This neural damage is likely to be a handicap in difficult listening situations, especially as overt hearing loss (i.e. threshold elevation and hair cell damage) is added to the mix. Since existing federal guidelines on workplace noise exposure were derived based on the assumption that exposures producing no PTSs [permanent threshold shifts) are benign, a careful re-evaluation of these guidelines is warranted if hidden hearing loss is to be prevented as well.
However, based on current research, according to this author, “An exciting aspect of this work is the notion that some of the hearing handicap in sensorineural hearing loss might be treatable or preventable.”
Building on this idea is an article by a group of researchers published in Frontiers in Molecular Neuroscience. Looking at new studies of the relationship between SNHL in aging and nutritional status it appears with possible dietary supplementation to prevent and possibly repair damage before it becomes irreversible. This article discusses up epidemiological studies that demonstrate “correlations among the nutritional condition, increased total plasma homocysteine (tHcy) and SNHL.” According to the authors, it seems that “Several human genetic rare diseases are also associated with homocysteine (Hcy) metabolism and SNHL confirming this potential link.”
In simpler terms, it appears from genetic examples, preliminary research and experimental data that homocysteine metabolism, in particular elevated homocysteine level is one of the keys to understanding hearing damage. As a corollary, it seems at least possible that when homocysteine levels are high and there are signs of beginning SNHL especially in the area of difficulties understanding spoken words in noisy environments, trying to lower elevated homocysteine with nutritional supplements might help. In addition, as people age, it becomes more difficult to convert folate from food sources to the necessary type used by the body to clear out homocysteine. This is borne out by several studies.
In one report looking at people over 60 years old, individuals with “normal hearing had normal folate levels, while those with hearing loss had low folate levels. In the Blue Mountains Hearing Study, a survey which checked nearly 3,000 people who were 50 years or older, “Participants with elevated tHcy (>20 micromol/L) concentrations had a 64% increased likelihood of prevalent hearing loss (>25 dB HL).” Furthermore, “Low serum folate levels (<11 nmol/L) increased the odds of prevalent mild hearing loss (>25-40 dB HL).” 
Findings such as these and others may suggest that as individuals age, checking homocysteine and folate levels, which also are related to other health considerations, might be worth doing occasionally, most especially in those experiencing hearing loss.
Liberman, M.C. “Noise-induced and age-related hearing loss: new perspectives and potential therapies,” [version 1; referees: 4 approved] F1000Research 2017, 6 (F1000 Faculty Rev):927 (doi: 10. 12688/f1000research, 11310.1). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5482333/pdf/f1000research-6-12205.pdf accessed March 24, 2018.
Parearroyo T., et al. “Cochlear Homocysteine Metabolism at the Crossroad of Nutrition andSensorineural Hearing Loss,” Frontiers in Molecular Neuroscience, 25 April 2017, 10: 107. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5403919/ accessed 3/24/2018.
Lasisi A.O., Fehintola, F.A., and Yusuf ,O.B. “Age-related hearing loss, vitamin B12, and folate in the elderly,” Otolaryngology—Head and Neck Surgery, 2010 Dec;143(6):826-30. doi: 10.1016/j.otohns.2010.08.031. Epub 2010 Oct 25. https://www.ncbi.nlm.nih.gov/pubmed/21109085, accessed March 24, 2018.
Gopinath, B., et al. “Serum homocysteine and folate concentrations are associated with prevalent age-related hearing loss,” The Journal of Nutrition, 2010 Aug;140(8):1469-74. doi: 10.3945/jn.110.122010. Epub 2010 Jun 23. https://www.ncbi.nlm.nih.gov/pubmed/20573942 March 24, 2018.