Insulin-like Growth Factor 1 and Variation in Normal Hearing in Male Adolescents

Abstract

Insulin-like growth factor 1 (IGF-1) is a polypeptide hormone that is involved in various physiological and cellular functions. It plays a crucial role in foetal development, adolescent growth, and adult tissue homeostasis. While the exact relationship between IGF-1 and hearing remains unclear, previous research has suggested that IGF-1 is important for the development, function, and protection of the auditory system. It is proposed that variation of hearing within the normal range may depend on the natural variation in IGF-1 levels in utero as reflected by IGF-1 levels in adolescence. This study aims to investigate the influence of IGF-1 levels on the hearing ability of normal-hearing male adolescents. It is hypothesised that higher IGF-1 results in better normal hearing. This study assessed the influence of IGF-1 levels on peripheral hearing and central auditory processing separately. Auditory sensitivity was measured using three-alternative forced choice pure-tone audiometry, while the nonlinearity of the cochlea was assessed using Distortion Otoacoustic Product Emissions, and relative cochlear length was estimated based on the timing of Transient Evoked Otoacoustic Emissions. Additionally, the Frequency Pattern Test, Dichotic Digits Test, and Listening in Spatialised Noise - Sentences Test were used to evaluate temporal ordering, binaural integration, and spatial segregation, respectively. Cognition was assessed using the Test of Nonverbal Intelligence and digit span tests. There was no correlation between serum IGF-1 levels and hearing thresholds in male adolescents with normal hearing. This contrasts with a previous study that observed this effect in female adolescents, indicating that the effect of IGF-1 on hearing may differ due to sex differences. On the other hand, IGF-1 was associated with some aspects of peripheral hearing and central auditory processing. The findings suggest that IGF-1 may affect the Distortion Product Otoacoustic Emissions input/output growth function compression threshold of low frequencies in the cochlea and also play a role in the functional laterality of dichotic listening. Further research is needed to evaluate the potential biological differences that may cause IGF-1 to affect normal hearing differently. This will help with a better understanding of the clinical and therapeutic implications of IGF-1 for hearing.