Environmental and lifestyle factors involved in normal hearing function and age-related hearing loss

Background Until now, little is known about environmental/lifestyle factors underlying normal hearing function and age-related hearing loss (ARHL). To reach this goal we decided to run an epidemiological study on hearing quantitative and qualitative traits (analysing the low, medium and high Pure Tone Average-PTA) on subjects coming from several isolated populations from Europe, Caucasus and Central Asia. Methods 4401 subjects coming from Europe (Italy, Croatia and Ukraine), Caucasus (Armenia, Azerbaijan, Georgia) and Central Asia (Uzbekistan, Kazakhstan, Tajikistan and Kirghizstan) and ranging from 4 to 95 years were included in the analysis. Different thresholds (0.25, 0.5, 1, 2, 4, 8 kHz) as well as PTAs have been considered in the study. A medical examination has been performed in order to exclude pathological conditions related to the hearing impairment. A series of lifestyle/environmental factors have been tested including habits (smoking, drinking, etc.), diet (several foods and beverages intakes), level of education, etc. A model based on linear/logistic regression was used to fit PTAs to all the covariates (smoking, chocolate, coffee, tea, wine, beer, dairy products, hard-liquor) including sex and age. Results As regards hearing function, our results show, for the first time, that among eight analyzed variables only coffee consumption (but not the coffee intake) was strongly associated with better normal hearing function in particular at low and high frequencies in four out of ten countries investigated (p=0.038 in Sardinia, 0.006 in Southern Italy, 0.017 in Azerbaijan, 0.016 in Tajikistan). As represented in the Figure 1, in the coffee-drinkers, the hearing function improves on average of 5.01 dB in Tajikistan. No association was found in the other populations, neither with other substances or coffee intake. In this light, we might suppose a connection between specific populations/communities, genes and environment. As regards ARHL phenotype, we found a strong association in two Italian isolated populations (p=0.02 for Sardinia, and p=0.05 for Southern Italy), in which a lower level of education is associated to an increased susceptibility to ARHL (Figure 2). Conclusions These data demonstrate, for the first time, a relationship between coffee consumption and a better hearing function, and confirm the relevance of a higher education in protecting against ARHL. The understanding of lifestyle/environmental risk factors will help us in developing new preventive strategies for ARHL.