Hearing loss is one of the common health problems among individuals ages 20 to 69 years in 2011 and 2012 with the prevalence rate at 14% [1]. An increase of the elderly population and in the popularity of ear plug devices among young adults indicates a further expected increase in the prevalence rates of hearing loss. In addition, hearing loss affects social relationships with poor communications, causes social isolation and depression [2]. It also may lead to a low quality of daily life [3]. Mechanisms linked to hearing loss have been demonstrated with cochlear damage through oxidative stress and inflammation on auditory nerve cells, reduction of the cochlear blood flow, and sensorineural dysfunction from hair cell loss [4, 5, 6]. Generally, the cochlea is a sensitive organ and is highly susceptible to oxidative stress in the inner ear [7]. Thus, it is important to identify ways to delay hearing loss.

Previous cross-sectional studies on diets that include antioxidants such as vitamins [8, 9] and β-carotene [10] have demonstrated inverse associations with hearing loss. However, previous studies have primarily focused on individual nutrients and dietary patterns. In another crosssectional study, the “Healthy Dietary Pattern”, mainly consisting of fruit, vegetables, and milk, indicated an inverse association with hearing loss [11]. Although dietary patterns were derived from various food groups, individual food group-based associations with hearing loss were not specified. It is important to investigate food group-based associations in order to provide more practical guidelines in terms of specific food choices that could help delay hearing loss.

Therefore, the associations of food group intake with hearing loss need to be investigated to specifically identify which food groups attribute to exacerbating or delaying hearing loss in the general population in order to establish more practical guidelines. Thus, we investigated an association between food groups and hearing loss in a large cross-sectional study of 1,312 participants from the Korea National Health and Nutrition Examination Survey (KNHANES).

Table 1 shows the general characteristics of all the 1,312 participants. The average age was 50.53 years. The average age of participants with hearing loss was significantly higher than those without hearing loss (55.60 vs. 49.56, P < 0.001). Participants with hearing loss were likely to be men than women (58.46 vs. 40.75, P < 0.001). Furthermore, the proportion of current smokers was greater in those with hearing loss than in those without (P < 0.001). However, no differences between participants with and without hearing loss in BMI, energy intake, physical activity, and alcohol drinking were found. Additionally, the prevalence rates of hypertension and diabetes were different between those with and without hearing loss.

Table 2 shows the characteristics according to the tertile ranges of the two food groups of vegetables and nuts. Participants in the groups of higher vegetable intake were more likely to be women (46.80%, 54.29%, 69.69%: P < 0.001), less likely to consume alcohol (15.91%, 11.38%, 9.41%: P = 0.030), less likely to smoke (29.98%, 16.40%, 15.09%: P < 0.001). Individuals in the group of higher intake of nuts were likely to be older (P < 0.001), less likely to have total energy intake (P < 0.001), likely to be women (P < 0.001), less likely to have alcohol consumption (P = 0.030), and less likely to currently smoke (P < 0.001).

Table 2
Characteristics of the study participants according to vegetables and nuts food groups (n=1,312)

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Table 3 shows the associations between the various food groups and hearing loss among 1,312 participants from the general population. As compared with participants in the lowest tertile, those participants in the highest tertile of vegetables and nuts food groups were less likely to have hearing loss (P for trend = 0.019 and 0.020, respectively).

Table 3
Associations between food groups and hearing loss (n=1,312)

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We found significant inverse associations between intakes of vegetables and nuts food groups and hearing loss among 1,312 participants aged between 40 to 64 years from a general population, after adjusting for confounding variables of age, total energy intake, sex, drinking, BMI, smoking, diabetes, hypertension, and physical activity. This study was unique in that it reported food group-based associations with hearing loss, suggesting a more practical dietary guidelines with specific food choices that could help delay hearing loss.

Our findings of significant inverse associations between vegetables and nuts food groups with hearing loss are concurrent with previous cross-sectional studies that suggested antioxidants in foods to delay hearing loss by preventing sensorineural impairment in the cochlea [8, 9, 10]. A prospective cohort showed a positive association with high sugar foods on age-related hearing loss [22]. In addition to studies with a nutrient focused approach, a previous study with dietary patterns presented a significant inverse association of hearing loss with a Healthy Dietary Pattern that was mainly featured with food groups of cereals, fruit, bread, vegetables, and milk [11]. As noted in our study, the vegetable food group, a part of the Healthy Dietary Pattern, indicated a significant inverse association on hearing loss [11]. Vegetables are known to provide vitamins, minerals, and fibers. These nutrients of vitamin A [8], vitamin C [10], folate [9] and vitamin E [8] have been demonstrated to have inverse associations with hearing loss. Folate deficiency has been reported to cause damage to the neurons and the vessels of the auditory system [9, 23, 24]. Vitamin B12 deficiency has also been shown to increase homocysteine level which promotes free radical formation and exerts a thrombogenic effect on the blood flow in the cochlea [25]. Additionally, other nutrients like riboflavin, retinol, and niacin have an inverse correlation with hearing loss in older adults [26].

Our findings also demonstrated an inverse association between nuts food group and hearing loss. Nuts, such as peanuts and chestnuts, are known to contain monounsaturated fatty acids like oleic acid [27], selenium, zinc, and vitamin E, which are demonstrated to be antioxidants [28], that protect the auditory nerves [29], have beneficial effects on the blood vessels in the cochlea [30], and help reduce inflammation [31].

The underlying mechanisms of the association linked to the food groups and hearing loss have not been fully elucidated. Our current findings align with previous suggestions of antioxidants and anti-inflammatory agents in the vegetables and nut food groups contributing to decreasing the risk of hearing loss. One of possible mechanisms of exacerbating hearing loss is that reactive oxygen species in the inner ear induce neuronal cell impairment and affect t he c ochlear b lood f low [32, 33]. Vitamins from vegetables have been demonstrated to act as antioxidants, removing singlet oxygen [10, 34]. Monounsaturated fatty acids and minerals from nuts food group have also been shown to reduce inflammatory markers [35]. The vegetables and nuts food groups decrease oxidative stress and also reduce proinflammatory markers.

Although participants in the middle tertile showed a reduced likelihood of having hearing loss in the seaweed and fruit food groups, neither the seaweed nor fruit food groups showed the statistical significance of a quadratic term for hearing loss (P = 0.08 and 0.05, respectively). Additionally, multi-collinearity among independent variables as well as the correlation between vegetables and nuts food groups were examined and no collinearity was confirmed. Also, sex-specific difference was examined but confirmed not to be statistically significant. It was examined if BMI played a role as a mediator due to the suggested oxidative stress. Then, the test results confirmed that the BMI variable was not a mediator, but rather considered as a confounding factor.

Our study has its strengths and limitations that are taken into considerations when interpreting our findings. First, as our study population was a large and nationally representative sample from the general population, it gives enough statistical power to demonstrate significance and retains the capability to generalize our findings into other populations. Second, the food group-based approach of our current study contributes to establishing a practical guide geared toward delaying hearing loss. However, this study also has limitations. The study design was a cross-sectional study, which imposed a limit on examining causality. Furthermore, socioeconomic variables such as education or income were not included as part of the confounding variables, which may have affected the results.

In conclusion, we found that vegetables and nuts food groups had significant inverse associations with hearing loss among the 1,312 participants from a general population, after adjusting for confounding variables.