• Age-related hearing loss linked to folate deficiency

    August 2010 

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    The gradual loss of hearing is an inevitable consequence of aging. About 30-35 percent of adults between the ages of 65 and 75 years and half those over 75 have some degree of hearing loss. In older adults, it is second only to arthritis as a handicapping condition. As the population ages, more effort is being made to identify the risk factors and preventive measures needed to relieve the burden of this impairment on the individual and those with whom he or she communicates.

    Several studies in recent years have suggested nutrition may play a role in hearing loss. 

    Several studies in recent years have suggested nutrition may play a role in hearing loss, particularly a lack of folate and vitamin B-12 in the diet. The largest of the studies, the Blue Mountains Hearing Study, is a population-based survey of age-related hearing loss, or presbycusis, conducted from 1997-99 and 2002-04.

    Researchers at the University of Sydney in Australia measured age-related hearing loss, in 2,956 participants age 50 and over. They were looking for an association between serum concentrations of folate, a naturally occurring folic acid in the body, and vitamin B-12 and the risk of age-related hearing loss. Both of these micronutrients determine the levels of homocysteine, an amino acid, in the blood. Elevated levels of homocysteine, which may be caused by a folate or B-12 deficiency, are associated with increased risk for cardiovascular disease and stroke.

    “Most hearing loss in the elderly is associated with cochlear dysfunction, and cochlear function is reliant on adequate vascular supply,” the authors wrote in the August 2010 issue of The Journal of Nutrition.

    How the study was conducted

    Study participants were interviewed in person, then blood samples were drawn and hearing tests conducted. They were asked questions about family hearing loss, past medical or surgical treatment of otologic conditions, diseases associated with hearing loss, and risk factors for ear disease. Other hearing related questions addressed exposure to noise at work, during military service or leisure activities.

    Researchers found that folate levels below 11 nanomoles per liter were associated with an increased risk of age-related hearing loss. 

    After adjusting for these variables, researchers found that folate levels below 11 nanomoles per liter were associated with a 34 percent increased risk of age-related hearing loss. Nearly two out of three people with elevated homocysteine had a hearing impairment, compared to less than one-third of those with normal levels. Participants with low serum vitamin B-12 were not more likely than those with normal vitamin B-12 concentrations to have hearing loss.

    Study limitations

    The researchers cautioned that, although they attempted to adjust for confounders such as work-related hearing loss, errors might have been made in their analyses. Additionally, lifestyle factors such as alcoholism and a lower intake of enriched cereal grain products might contribute to low serum folate concentrations. Further studies are called for, they noted, to investigate whether higher levels of folate can actually reduce the risk of age-related hearing loss.

    Sources of folates

    Vitamins can supply 100 percent of the minimum daily requirement of folates, but a healthy diet is also necessary. There are many foods rich in folates, including broccoli, beans and peas, beef liver, spinach, asparagus, avocado, dry roasted peanuts, orange juice, and bananas.

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Page last updated: 8/7/2015 1:17:00 PM
  • What the news means for you

    Hearing loss may be inevitable result of aging

    Kristy S. Deep, MD
    Internal Medicine

    Wright, Heather, MDA great deal of research has gone into the investigation of aging: What causes us to age, in general? One of the more plausible theories nowadays involves free radicals that accumulate in the body, causing damage to cells and DNA in cells so they are unable to repair themselves, leading to aging. This has been demonstrated in various organs, and I don't think there's a separate, distinct process going on in the ear that causes hearing loss.

    In previous studies, scientists have tried to treat animals with various foods, drugs and supplements that would prevent the build-up of these free radicals. I think it is an interesting concept that, by doing so, humans could protect their cells and thereby slow the aging process. There are many different drugs and antioxidants like vitamin E that can have this effect. Folate is among those that has appeared to work.

    The Australian study is unique in that it was done on humans, whereas most have been done on lab rats. It's a very good study because it involved a large group of subjects and was placebo-controlled. It did show a very, very slight protection against hearing loss in the group that took folate. The group receiving the placebo showed some hearing loss over the four years of the study because they were getting older. In the folate group, the hearing loss was not as bad in the low- to mid-frequencies.

    One criticism of the study has been that the population is one that does not routinely add folic acid to foods, as compared to the United States where it is required to be added. In fact, the study participants had about 25-percent less folate in their diets than people in this country. So it's questionable as to whether the addition of this supplement would even be beneficial in the United States, where most people already get more than twice the minimum daily recommended amount of folate.

    In the Australian study, hearing loss was abated only a very slight amount over four years, but the thought is that adding folic acid over 20 to 30 years might make a significant difference. It would have to be started when a person is young, but nobody knows exactly what age that would be. The idea is to start giving the supplements before damage sets in and to continue giving them.

    “It did show a very, very slight protection against hearing loss in the group that took folate.” 

    Hearing loss starts early

    There have been some very interesting studies, showing that the aging process actually begins very, very early on. It has been suggested that hearing starts going downhill after age 12, and that's probably true. The part of hearing we lose first is in the very high frequencies. Experiments have demonstrated that, if you take certain high-frequency whistles into a classroom, the 35-year-old teacher won't be able to hear what the 15 year olds hear when you blow the whistles.

    The typical hearing test doctors do in their offices only goes up to about 8,000 hertz, that's high-frequency pitched sounds. We're actually able to hear up to 20,000 hertz, but really there are no sounds useful to us over about 6,000 to 8,000 hertz.

    Everybody will get some age-related hearing loss. In some people, it begins at 50 or 60 years of age; others won't notice it until they're 70 or 80. I often see one spouse bringing in the other, saying he or she "doesn't hear me anymore." Age-related hearing loss happens so slowly that a person may not even realize it, but it builds up so that eventually the person is missing a lot.

    Noise exposure

    Exposure to loud noises over a period of time causes the exact same type of hearing loss as age-related hearing loss. The damage is done through the same pathway - free radicals. Men are more likely to have this type hearing loss because they generally are exposed more to noises such as gunfire and loud engines.

    Short-term studies in animals have shown that these same supplements - vitamin E, folic acid and beta carotene - that protect against free radicals help protect the ears against hearing loss. If we gave people these drugs before they were exposed to noise and immediately afterward, it might protect them.

    Hearing aids

    The first signs of hearing loss are difficulty understanding conversations when there is a lot of background noise, as in a restaurant, and family members commenting on a person's inability to hear. A hearing test conducted by an audiologist will define the level of hearing impairment and confirm nerve damage. Once you have a hearing loss, you should get a test yearly, just as you do for your eyes when you wear glasses or contacts.

    A hearing aid probably would be helpful when hearing loss is more than 30 decibels, which is about the level of a whisper. Hearing aids can be expensive and adjusting to them may be difficult. It's when the benefits outweigh costs that you should get one. If you wait too long, the hearing loss may be so severe a hearing aid isn't much help.

    More studies needed

    The Australian study is really early, cutting edge research. The researchers were able to study folic acid in humans because it is a food and not regulated as drugs would be. Often, a dietary supplement or a plant - digitalis, for example - can be refined into a drug that is more potent and purified as well as regulated. For now, everyone would be better off making sure they have a well balanced diet containing adequate folic acid, vitamin B-12, beta carotene and good antioxidants.

    Dr. Deep is an internist, director of the palliative care service and assistant professor of internal medicine in the UK College of Medicine.

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