By Stephen Daniells, 24-Jun-2010
Low blood levels of folate are associated with a 35 percent 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”.
Folate and folic acid
Folate is found in foods such as green leafy vegetables, chick peas and lentils, and an overwhelming body of evidence links has linked folate deficiency in early pregnancy to increased risk of neural tube defects (NTD) – most commonly spina bifida and anencephaly – in infants.
This connection led to the 1998 introduction of public health measures in the US and Canada, where all grain products are fortified with folic acid – the synthetic, bioavailable form of folate.
Preliminary evidence indicates that the measure is having an effect with a reported 15 to 50 per cent reduction in NTD incidence. A total of 51 countries now have some degree of mandatory fortification of flour with folic acid.
Source: Journal of Nutrition
Published online ahead of print, doi:10.3945/jn.110.122010
“Serum Homocysteine and Folate Concentrations Are Associated with Prevalent Age-Related Hearing Loss”
Authors: B. Gopinath, V.M. Flood, E. Rochtchina, C.M. McMahon, P. Mitchell