Did You Catch the Latest on Vitamins and Hearing Loss?
Attentive readers of TalkingNutrition will remember our post from late last year on antioxidant vitamins and hearing loss. That study showed that intakes of vitamins C, E and beta-carotene was associated with better hearing in a US population. Another group of researchers lead by Kang has recently performed a similar analysis of a different population: a representative sample of older Korean adults. The researchers used data from the Korean National Health and Nutrition Examination Survey (KNHANES) on 3253 subjects aged between 50 and 80 years. After excluding subjects with conditions known to affect hearing loss, the results of subjects’ hearing tests were compared to intakes of carotenoids, retinol, thiamin, riboﬂavin, niacin, and vitamin C. Information on risk factors for hearing loss such as smoking, history of work in a high-noise environment and exposure to explosive noises such as gunshots were also assessed.
The authors found that men had worse hearing than women, and that age increased likelihood of hearing loss. People with exposure to occupational noise had worse hearing at the mid-frequency ranges that those without this exposure. Less than half the population consumed riboflavin, niacin, vitamin C and vitamin A at recommended intakes, and fewer women met recommendations than men. People in the highest quartile of intakes for all the nutrients studied had significantly better hearing than those in the lowest quartile. Surprisingly, people with higher levels of vitamin D had worse hearing than people with lower levels at the mid- and high-frequency levels. Use of dietary supplements was associated with better hearing.
The authors also conducted a multivariate analysis as nutrient intakes, and hearing ability, both tended to decrease with age. After they adjusted for factors such as sex, age and exposure to occupational noise, they found only that higher vitamin C intakes were still associated with better hearing.
How could nutrition affect hearing? There are two possible mechanisms. The first one relates to oxidative stress within ear cells. Like all other cells, the cells involved in hearing are also affected by the damaging effects of oxidative stress. Over time, the damage builds up and eventually affects hearing. This is why older people are more likely to have hearing problems. Kopke and co-workers describe how improving oxidative stress defenses can reduce oxidative damage to cochlear hair cells, in an animal model. The second mechanism relates to the role that nutrition plays on the immune system. For example, vitamin A deficiency has been shown to increase rates of ear infections in humans. Although most research is focused on children, who have much higher rates of ear infections than adults (for example, see a clinical trial follow-up by Schmitz and colleagues), vitamin A deficiency reduces the effectiveness of barrier cells in the ear (see Bielsalski’s review) and may affect how well the cells in the ear work. The authors suggest that the use of dietary supplements may be more effective in the elderly, who tend to have poorer nutrient intakes. Preventing hearing loss is yet another benefit of a healthy diet and lifestyle.
Kang JW, Choi HS, Kim K, Choi JY. Dietary vitamin intake correlates with hearing thresholds in the older population: the Korean National Health and Nutrition Examination Survey. First published March 19, 2014 doi: 10.3945/ajcn.113.072793
Biesalski HK, Wellner U, Stofft E, Bässler KH. Vitamin A deficiency and sensory function. Acta Vitaminol Enzymol. 1985;7 Suppl:45-54. http://www.ncbi.nlm.nih.gov/pubmed/3916045
Choi Y-H, Miller JM, Tucker KL, Hu H, Park SK. Antioxidant vitamins and magnesium and the risk of hearing loss in the US general population. 2013 Am J Clin Nutr doi:10.3945/ajcn.113.068437
Kopke RD, Coleman JK, Liu J, Campbell KC, Riffenburgh RH. Candidate's thesis: enhancing intrinsic cochlear stress defenses to reduce noise-induced hearing loss. Laryngoscope. 2002 Sep;112(9):1515-32. http://www.ncbi.nlm.nih.gov/pubmed/12352659
Schmitz J, West KP Jr, Khatry SK, Wu L, Leclerq SC, Karna SL, Katz J, Sommer A, Pillion J. Vitamin A supplementation in preschool children and risk of hearing loss as adolescents and young adults in rural Nepal: randomised trial cohort follow-up study. BMJ. 2012 Jan 10;344:d7962. doi: 10.1136/bmj.d7962. http://www.ncbi.nlm.nih.gov/pubmed/22234907