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Submission: July 22, 2018; Published: July 25, 2018
*Corresponding author: Michael AB Naafs, Internist-endocrinologist with a long clinical career in internal medicine and endocrinology, Naafs International Health Consultancy, Dutch, Europe, Email: email@example.com
Recent research showed an association between nutritional iodine deficiency and hearing loss. Little is known about iodine deficiency in relation to auditory function. Even more controversial is the role of vitamins, antioxidant and mineral supplements in preventing or reducing hearing loss. The advent of nutrigenomics is expected to build on new research in the field of “nutritional hearing loss”.
Recently, researchers reported that U.S. teens with the lowest levels of urinary iodine were five times more likely to have hearing loss associated with speech comprehension than their peers with higher iodine levels . Iodine deficiency affects an estimated 241 million school-aged children in the world. Little is known about iodine deficiency in relation to auditory function, except for the fact that deaf-mutism is one of the features of cretinism . Hearing loss is the fourth-leading cause of disability worldwide. About 80% of people with hearing loss live in low-and middle-income countries. John Hopkin’s researchers studied 2200 children in Nepal, who were undernourished during their preschool years. They found that those who were undernourished in their preschool years were about twice as likely to have hearing loss 16 years later than those who were better nourished as young children . Previous studies have linked deficiencies of micronutrients, including vitamin A and zinc to hearing impairment . although this was believed to be related to an increased incidence of otitis media in malnutrition .
Of course, it is far more difficult to quantify the quantity and quality of foods consumed over a long period of time, than it is to quantify hearing loss at a moment in time. In high-income countries, large population studies have reported protective risk ratios against hearing loss with higher dietary intakes of fish, long chain polyunsaturated fatty acids (PUFAs) folate, beta-carotene and vitamins A,E, and C . Heavy metals have been implicated in hearing loss . All these studies add to the developing story that adequate and balanced nutrition during pregnancy, infancy may reduce hearing loss globally and across the life-span. Accurate, faster and less costly studies for measuring diet, status of micronutrients, and hearing are needed to investigate the role
of nutrition in hearing loss, both in under-and over-nutrition. In this mini-review the available evidence for the role of nutri
tion in hearing loss will be discussed. Nutrition and tinnitus is beyond the scope of this review.
The occurrence of congenital deafness, mutism and goiter unassociated with cretinism or mental retardation in euthyroid patients is known as Pender’s syndrome. It is estimated that 4-10% of children with congenital deafness suffer from this condition . The perceptive hearing loss is considered to be present at birth although it is frequently not recognized for years. The goiter becomes only apparent in the prepubertal years. The cause of the hearing defect is a congenital bilateral malformation of the cochlea of the Mendini type. The thyroid defect has been shown to be a partial defect in iodine organocation leading to the underproduction of thyroxine, progressing to a nodular goiter. The autosomal recessive mutant gene is responsible for both the deafness and goiter . Hearing impairment was also reported in thyroid hormone resistance syndromes caused by mutations in the beta-thyroid hormone receptor gene (beta TR gene).Because of its otogenic distribution in the cochlea the beta-TR may have a pivotal role in the development of hearing impairment in thyroid hormone resistance syndromes . Hearing loss in thyroid disease is in addition to congenital hypothyroidism most commonly associated with hypothyroidism due to autoimmune disorders, as e.g. Hashimoto’s disease .
Hearing loss associated with Graves’disease (hyperthyroidism) and or propylthiouracil treatment is less commonly reported. Taken together it is not surprisingly the role of iodine in hearing loss has been investigated further. Van den Briel et al . investigated 197 school children in an iodine-deficient area in northern Benin. In this randomized placebo-controlled intervention trial with an observation period of 11 months a toGlobaltal of 97 children received an oral dose of iodized oil containing
540mg/l, while 100 children received a placebo. After 3-4 months
supplementation, the whole population began to have access
to iodized salt. Urinary iodine was measured at the beginning
and the end of the study, as well as thyroglobulin (TG) concentrations.
In this mildly iodine-deficient child population children
with higher TG concentrations had significantly higher hearing
thresholds in the higher frequency range (>2000Hz) than children
with lower serum TG concentrations. Moreover, children
with lower hearing thresholds performed significantly better
on the mental tests used. The authors concluded that adequate
iodine intake through salt iodization programs and other means
are crucial . Males Bootstrap and Mackenzie reviewed the literature
regarding the role of iodine and hypothyroidism on the
auditory system .
On the internet a plethora of vitamin supplements, antioxidants
and minerals are offered to prevent or reduce age-related
and noise-related hearing loss. Is there any scientific base for
these claims? Numerous animal studies have shown the otoprotective
effects of free radical scavengers, and the antioxidant
properties of vitamin C,E and beta-carotene have been demonstrated
to protect from inner ear damage caused by aminoglycosides,
cisplatin, acoustic trauma, noise exposure and presbyacusis
[14,15]. However, the limited number of human studies have
yielded conflicting results. The Health Professional Follow-up
Study enrolled 51.529 male participants who were 41-75 years
of age at baseline in 1986.During a 20 year follow-up participants
filled out yearly questionnaires about diet, medical history
and medication use. Of the 33.884 men who responded to the
long form questionnaire,7092 (20,3%) reported a diagnosis of
hearing loss. Overall the study found no prospective association
between vitamin C,E, beta-carotene,B12 or folate intake and incident
hearing loss in men 60 years and older .
The Australian Blue Mountain Study enrolled 2956 participants
aged 50 plus at baseline that have been followed from
1979-9 to 2002-4. Dietary data were collected in a semi-quantitative
food frequency questionnaire. Intakes of alpha-carotene,
beta-carotene, beta cryptoxanthin. lutein, zeaxanthin, lycopene,
vitamins A,C,E, Iron and zinc were calculated. The authors
concluded dietary vitamin A and vitamin E were significantly associated
with the prevalence of hearing loss but not with the incidence
of hearing loss. Dietary antioxidant use did not increase
the risk of hearing loss . A NHANES cohort (2001-2004) was
studied by Choi et al for the associations between intake of antioxidant
vitamins (daily beta-carotene and vitamins C and E and
magnesium) and hearing thresholds and explored their joint effect
in U.S. adults. A cohort from 2592 participants, aged 20-69
years, were studied.in the NHANES 2001-2004 cohort. Higher
intakes of antioxidants and magnesium, individually and in combination
appeared to be associated with a lower risk of hearing
This cross-sectional finding does not allow for the conclusion
that antioxidants and magnesium have a causal protective
effect on hearing loss . The Conservation of Hearing Study
examined risk factors for hearing loss among participants in the
Nurses Health Study 2,an ongoing cohort of 116.430 female registered
nurses in the U.S. aged 25-42 year at cohort inception
in 1989 . Participants have been followed by biennial mailed
questionnaires asking for diet information, life style, incident disease,
and various health outcomes.After1.084.598 person-years
of follow-up 12.789 cases of hearing loss were reported in this
white women study. Higher intakes of carotenoids, especially of
beta-carotene and beta-cryptoxanthin were statistically associated
with a lower risk of hearing loss. Higher vitamin C levels
from supplements were associated with a higher risk of hearing
loss. Higher folate levels tended to be associated with lower risk.
No significant associations were observed between intake of vitamin
A, other carotenoids, or vitamin E and risk of hearing loss
in these women .
Ibrahim et al  reviewed the evidence for an effect of adjuvant
vitamin/mineral therapy for sudden sensorineural hearing
loss but could not find convincing evidence as the vitamins
were combined together or were used in combination with selenium.
From 446 manuscripts only 3 were eligible and were
included with 279 patients following Cochrane bias criteria.
So, these questionnaire studies will not give the answer if vitamins
,antioxidants and minerals are beneficial in preventing or
reducing hearing loss. Multivitamin/multimineral supplements
are widely used in the US ,sometimes containing 20 different of
each per supplement. This reduces deficiencies in micronutrient
in take, but has also the potential for exceeding tolerable upper
intake levels. The advent of nutrigenomics and the enhanced ability
to directly study the interaction between nutrition and genetic
variants and expression will allow for more targeted studies
in the field of personalized nutrition. This will also be the case in the field of ”nutritional hearing loss”. The ongoing Cocoa and
Multivitamin Outcomes Study (COSMOS) is expected to build on
this research and provide additional insights in these areas .
Recent research showed an association between iodine
deficiency and hearing loss [1,3]. Although the role of thyroid
hormone in auditory development is fairly well established in
congenital hypothyroidism and thyroid hormone resistance syndromes,
little is known about iodine deficiency in relation to auditory
function Population questionnaire studies did not resolve
this problem. The role of vitamins, antioxidants and minerals in
“nutritional hearing loss” is even more controversial. The advent
of nutrigenomics and the ability to directly study the interaction
between nutrition and genetic variants will allow for more targeted
studies, also in the field of “nutritional hearing loss”.