The Role of Nutrition in Healthy Hearing
Healthy aging, or successful aging, occurs when an increased risk of disease and disability with advancing age is neither inevitable nor caused by intrinsic aging processes. Rather, healthy aging is a result of lifestyle and other factors that may be age related but that are not age dependent (Rowe & Kahn, 1997). Interest in successful aging is reflective of the unprecedented growth in number and proportion of older adults in the United States. It is estimated that by 2050, the number of Americans over age 65 will reach 89 million—more than double the number in 2010 (Centers for Disease Control and Prevention [CDC], 2013). Hearing loss and balance issues are very common in older adults, with over 50% of adults reporting deficits in hearing (Goman & Lin, 2016) or balance (Semenov Bigelow, Xue, du Lac, & Agrawal, 2016). However, are those deficits an inevitable, intrinsic part of aging?
Shangri-La of Hearing
Have you heard of the Mabaan tribe? In the 1960s, an otologist named Samuel Rosen, known for developing the stapes mobilization procedure for otosclerosis, became intrigued with understanding the relationship between aging and hearing loss; i.e., Does age cause hearing loss or do factors associated with aging cause hearing loss? Specifically, Rosen was interested in determining if hearing loss with age was due to the cumulative effect of noise in modern civilization or atherosclerosis and high blood pressure also often associated with aging. Addressing this mystery required studying a group of individuals with limited noise exposure or limited evidence of atherosclerosis and high blood pressure.
While demonstrating his stapes technique in Germany, Rosen met Dietrich Plester, a medical doctor who described his recent adventures in Sudan and a potential population that could possibly help address the mysterious relationship between aging and hearing loss. The Mabaans were a tribe in an isolated region of southeast Sudan. They had no exposure to the mechanical noise of modern civilization, they were very active, and they maintained a frugal diet consisting mainly of ground millet, fish, nuts, and dates. They were also known for their keen sense of hearing. Rosen, Plester, and colleagues set out to learn more about the tribe in a series of studies. In their first study, hearing assessment demonstrated essentially normal thresholds from the 1st to the 8th decade of life ( <25 dB HL) at 6 kHz and below. Yet, the average threshold for 6 kHz at 15 years of age was 0 dB HL and at 75 years of age was 15 dB HL. Compared with American males with reported minimum noise exposure, hearing level started at the same place, 0 dB HL, at 15 years of age at 6 kHz. However, by age 75 years, American males had average thresholds of 60 dB HL at 6 kHz, corresponding to a difference of 45 dB (Rosen, Bergman, Plester, El-Mofty, & Satti, 1962).
Higher frequencies were included in follow-up studies. Fifty-three percent of 70- to 79-year-olds in the Mabaan group could hear 14 kHz compared with only 2% in American, German, and Egyptian groups. There was no noted differences between the American, German, and Egyptian populations (Rosen, 1969). In addition, the blood pressure of the Mabaans was constant from childhood to old age, with nearly nonexistent evidence of cardiovascular disease (normal cholesterol and electrocardiograms). The limited noise exposure and lack of atherosclerosis or hypertension did not allow Rosen to answer his original question. But did he show that hearing loss was not necessarily an inevitable part of aging?
Indeed, there was a progressive change in the hearing of the Mabaans, although to a smaller extent than in other populations. In addition, not all of the older subjects could hear at 14 kHz. Further, Rosen reported that the few Mabaans who left the village to live in the city (Khartoum) showed evidence of hearing loss and cardiovascular disease (e.g., elevated cholesterol). In other words, the studies of Rosen and colleagues demonstrated that there is some component to loss of hearing that may be reflective of age itself, but it is possible that this component is within the normative range—at least, for frequencies important for speech perception. Still, extreme basal regions of the cochlea may be more sensitive to general wear and tear without obvious noise, drug, or cardiometabolic insults.
Determinants of Hearing Loss
Age-related hearing loss is a result of our lifetime of cumulative exposures to extrinsic factors (e.g., noise) modified by susceptibility related to intrinsic factors (e.g., genetics). We must remove from our mentality the assumption that hearing loss is an inevitable part of aging and, rather, view hearing loss as a neurosensory medical pathology mediated greatly by lifestyle—much like the way we view disorders such as type 2 diabetes.
The question remains: How can we modify risk to be more like the Mabaans as we age—that is, preserve hearing with age? First, we must consider determinants of hearing loss. Table 1 shows factors that influence susceptibility to acquired hearing loss. These factors fall into three primary categories: modifiable, non-modifiable, and possibly modifiable.
We cannot change our genetics (at least, not currently), our sex (and there is limited knowledge of how gender reassignment may affect susceptibility), or our race/ethnicity. Nonetheless, these are factors that can greatly influence susceptibility to hearing loss. It is reasonable to assume that the hearing of the Mabaans was a manifestation of some genetic factor. Yet, there was some suggestion that deficits did present with city life and modern civilization exposure. Similar effects to the noise exposures of modern civilization have been described in other populations (Goycoolea et al., 1986). This article does not focus on these factors but, rather, focuses on things we can modify.
We can modify our exposure to noise and other environmental insults, and we can possibly modify our health and our education—although it is not necessarily easy to modify the latter two. Lifestyle (including diet) is widely recognized as a meaningful determinant of all major health complications, including hearing loss. In addition, lifestyle is modifiable. However, modification of lifestyle is also complicated. In general, healthy living is a universal concept, but challenges can be unique depending on geographic region, sociocultural issues, and other determinant factors listed above (e.g., age, sex, etc.). Since the second half of the 20th century, society at a global level has changed how we eat—from largely plant-based diets with high micronutrient density to higher fat and more energy-dense diets. This is further affected by a shift to more sedentary activity levels. The cumulative effect is individuals who lack appropriate micronutrients but are also obese. Poverty and access to nutritional foods is an overarching issue, but an additional element at play is health and nutritional literacy to increase acceptance of better health choices and behaviors.
Successful Hearing With Age
Lessons can be learned from the literature on lifestyle and general health. Rowe and Kahn (1997) proposed a model of successful aging that included three main components: avoidance of disease and disability, maintenance of cognitive and physical function, and active engagement with life. Hearing loss is a condition that intersects, to some extent, with each of these three components. Therefore, if we can effectively manage or prevent hearing loss, we can reduce social isolation (avoidance of disease and hearing loss), improve communication (engagement with life), and potentially influence cognitive function (high cognitive and physical function)—thus leading to more successful aging.
Figure 1. Successful Aging and Hearing
Lifestyle factors (e.g., nutrition, physical activity, smoking, etc.) also have a significant influence on aging. Furthermore, they alter risk for disease and disability and are recognized determinants for cognitive decline and dementia (Gagliardi, Papa, Postacchini, & Giuli, 2016). This information is important, given evidence that hearing loss may also influence risk for cognitive decline.
Since the early work of Rosen, numerous studies have examined the relationship between lifestyle factors and hearing in both animals and humans. In general, these studies have demonstrated that diets inadequate in micronutrients, high in caloric intake, and high in dietary lipids increase the risk or odds of hearing loss. On the contrary, diets rich in micronutrients (in particular, those with antioxidant properties), low in caloric intake, low in dietary lipids (in particular, saturated fat), and low in sugar reduce the risk or odds of hearing loss. For review, see Le Prell and Spankovich (2013) and Spankovich (2014). Physical activity in particular has been demonstrated as a significant risk reduction factor, with increased physical activity and decreased sedentary behavior associated with reduced odds of hearing loss (Loprinzi, 2013).
Reduced risk for hearing loss is associated with dietary manipulations in studies of age, noise, and drug-related hearing loss, but variation is noted. For example, in animal studies, dietary antioxidant supplementation has generally demonstrated reduced susceptibility to noise and drug-induced hearing loss. However, in models of aging, the relationship is less clear. This may be due to genetic factors of the animal that may or may not be influenced by diet, complexities of aging, and type, dose, and delivery method of the antioxidant agent.
Meta-analyses of antioxidant supplements in prevention of other chronic disease and disorders overall showed no protective benefit and possible harmful consequences in well-nourished populations (Bjelakovic, Nikolova, & Gluud, 2014). Similar evidence has been suggested with hearing and supplemented vitamin C (Curhan et al., 2015). This does not mean that supplements cannot play a role in successful hearing with age, but we should be cognizant of their limitations. These agents may be more applicable to acute challenges (e.g., noise exposure) or specific nutrient deficiencies until we better understand the long-term implications. Otoprotective agents (drugs to prevent hearing loss) that are being developed, including those based on dietary factors, should be fully vetted for interactions and long-term effects. It is worth noting that no studies have shown that antioxidants derived via diet have negative consequences.
Rather than focus on specific nutrients, we may find more meaning in the consideration of dietary patterns. Dietary patterns take into account the type of diet on the basis of food types (e.g., vegetarian), statistical patterns, and/or indices of quality. We have recently published a series of studies on diet and hearing based on the healthy eating index (HEI), which is a measure of how well a diet conforms to the recommended dietary guidelines of the U.S. Department of Agriculture (USDA). The HEI provides a score on a scale of 0 to 100, with 100 being the maximum “healthy” score and indicating that the individual is meeting approximately 100% of the USDA’s recommendations. The score is a sum of subcomponents that examine variable aspects of diet. Some components provide higher scores with higher dietary intake (e.g., fruits), and others provide lower scores with higher dietary intake (e.g., sodium). The average HEI score for U.S. adults is 64. Our analyses using the National Health and Nutrition Examination Survey dataset showed a significant relationship between HEI and hearing loss, where higher HEI (better diet) was associated with lower thresholds (better hearing) and reduced report of tinnitus (Spankovich & Le Prell, 2013, 2014). Specific subcomponents showing relationships to better hearing included (a) higher intake of vegetables and fruits as well as diet variety and (b) lower intake of sodium and saturated fat.
You may be wondering, “Is there a specific supplement or nutrient that my patient should take for better hearing?” At this time, I cannot advise a specific supplement or specific nutrients. Furthermore, no supplement is going to counteract an unhealthy diet or sedentary lifestyle.
What you can do is start the conversation about things we can control, such as hearing conservation strategies (e.g., using hearing protection, reducing noise exposure, etc.). Then, move to general recommendations of increasing physical activity and eating healthy. A good place to start for healthy eating recommendations is the USDA Dietary Guidelines. An eating plan that is well representative of the nutrient and dietary patterns shown to be associated with better hearing is the Dietary Approach to Stop Hypertension—or the DASH diet. The National Heart, Lung, and Blood Institute and the USDA promote the DASH diet as an ideal eating plan for all Americans. The DASH eating plan is rich in fruits, vegetables, low-GI foods, lean meats, fish, nuts, seeds, and beans with a limited intake of high-GI foods (e.g., sugar-sweetened foods and beverages), red meats, saturated fats, and sodium. The earlier we can incorporate health-promoting behaviors, the better.
In summary, successful hearing with age does not start with the ear but instead starts with health choices that influence our ability to successfully age. Hearing loss and other sensory functions can greatly influence aging and are, in turn, greatly influenced by our lifestyle and general health. As audiologists, we must consider our patients’ entire health and look at factors beyond the usual suspects (noise, age, drugs) to manage and prevent hearing loss today and in the future.
About the Author
Christopher Spankovich is Associate Professor and Director of Clinical Research for the Department of Otolaryngology and Communicative Sciences at the University of Mississippi Medical Center. Spankovich obtained his Master of Public Health degree from Emory University (Atlanta, Georgia); doctor of audiology degree (AuD) from Rush University (Chicago, Illinois); and PhD from Vanderbilt University (Nashville, Tennessee).