Study Title:

Folic Acid and Hearing Loss

Study Abstract

Elevated total serum homocysteine (tHcy) concentrations associated with vitamin B-12 or folate deficiencies may adversely affect blood flow to the cochlea, leading to age-related hearing loss (presbycusis). However, only 2 small cross-sectional studies have assessed the link between folate, vitamin B-12, or tHcy and presbycusis. We aimed to determine both the cross-sectional and longitudinal association between serum concentrations of folate, vitamin B-12, or tHcy and risk of age-related hearing loss. The Blue Mountains Hearing Study is a population-based survey of age-related hearing loss (1997–1999 to 2002–2004). Presbycusis was measured in 2956 participants (aged 50 y) and was defined as the pure-tone average of frequencies 0.5, 1.0, 2.0, and 4.0 kHz >25 dB hearing level (HL). Serum concentrations of folate, vitamin B-12, and tHcy were determined from blood samples. Participants with elevated tHcy (>20 µmol/L) concentrations had a 64% increased likelihood of prevalent hearing loss (>25 dB HL) [multivariate-adjusted odds ratio (OR) 1.64; 95% CI, 1.06–2.53]. Low serum folate levels (<11 nmol/L) increased the odds of prevalent mild hearing loss (>25–40 dB HL), multivariate-adjusted [OR 1.37 (CI 1.04–1.81)]. Serum vitamin B-12, however, was not significantly associated with prevalent hearing loss. Serum folate, vitamin B-12, and tHcy concentrations were also not significantly associated with an increased risk of incident hearing loss. Serum concentrations of tHcy and folate were associated with age-related hearing loss cross-sectionally, but no temporal links were observed, which could be due to insufficient study power. Further, large prospective studies will be required in the future to assess these associations.

From press release:

Low blood levels of folate are associated with a 35 per cent increased risk of hearing loss, says a new study from Australia that strengthens the link between B vitamins and hearing.

Findings published in the Journal of Nutrition indicated that vitamin B12 levels were not associated with hearing, however.

This is not the first time the B vitamin has been linked to the prevention of hearing loss, the most common sensory disorder in the United States, affecting more than 36 million people. In 2007 scientists from Wageningen University reported that folic acid supplements delayed age-related hearing loss in the low frequency region in a study of 728 men and women between the ages of 50 and 70 (Annals of Internal Medicine, Vol. 146, pp. 1-9).

Furthermore, in 2009 Boston-based researchers told the 2009 American Academy of Otolaryngology-Head and Neck Surgery Foundation (AAO-HNSF) Annual Meeting in San Diego that men over the age of 60 with high folate intake from foods and supplements had a 20 per cent decrease in risk of developing hearing loss.

Down Under

The Blue Mountains Hearing Study now adds to the small but growing body of science supporting folate for hearing. The study was based on a population of 2,956 people aged 50 and over.

Researchers at the University of Sydney examined blood levels of folate, vitamin B12, and homocysteine and correlated this with the risk of age-related hearing loss. The data showed that folate levels below 11 nanomoles per litre were associated with a 34 per cent increased risk of age-related hearing loss.

In addition, levels of homocysteine over 20 micromoles per litre were associated with a 64 per cent increase in the risk of hearing loss.

High blood levels of the amino acid homocysteine have been linked to a range of detrimental health conditions, including heart disease and dementia. Elevated levels of homocysteine are also said to adversely affect blood flow in the inner ear, which would increase the risk of age-related hearing loss.

Numerous studies have shown that B vitamin levels influence homocysteine levels in the blood.

While the data do show a correlation, they do not prove that higher levels of folate may reduce the risk of age-related hearing loss. Indeed, the researchers state: “large prospective studies will be required in the future to assess these associations”.

Study Information

Bamini Gopinath, Victoria M. Flood, Elena Rochtchina, Catherine M. McMahon, and Paul Mitchell.
Serum Homocysteine and Folate Concentrations Are Associated with Prevalent Age-Related Hearing Loss
Journal of Nutrition
2010 June
Centre for Vision Research, Department of Ophthalmology, Westmead Millennium Institute, University of Sydney, Sydney, NSW 2006, Australia.

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