Insulin-like growth factor 1 and hearing impairment in older adults: results from the English Longitudinal Study of Ageing

Abstract Background Age-related hearing impairment is the most common hearing disorder, affecting two-thirds of people aged over 70 years in the UK. It is a major cause of disability, with considerable social and health implications, accompanied by a major economic burden. With the condition essenti... Full description

Abstract Background Age-related hearing impairment is the most common hearing disorder, affecting two-thirds of people aged over 70 years in the UK. It is a major cause of disability, with considerable social and health implications, accompanied by a major economic burden. With the condition essentially incurable, the focus becomes identification of risk factors. The biological determinants of hearing impairment remain poorly understood. Despite a suggestion from animal studies that insulin-like growth factor 1 (IGF-1) is implicated in the development of hearing impairment, we know of no studies in human beings. Methods 4398 participants with no missing data (mean age at baseline 64·2 years [SD 8·1], 55% women) from the English Longitudinal Study of Ageing provided serum concentrations of IGF-1 in 2008 and 2012. We used the average of these two measurement when available, one if not. Hearing acuity was measured with a HearCheck Screener (Siemens, Erlangen, Germany) in 2014. Hearing impairment was defined as hearing fewer than all six tones, three with decreasing intensity at two frequencies (1 kHz and 3 kHz). Logistic regression models were used to estimate odds ratios (OR) of hearing impairment across five quintiles of IGF-1 concentration. Presence of interaction and non-linearity were assessed by likelihood ratio tests. Findings Mean IGF-1 was 16·1 nmol/L (SD 5·2). In the full analytical sample, IGF-1 was not associated with subsequent hearing impairment (OR per 5 nmol increase in IGF-1 1·01, 95% CI 0·94–1·09). However, this association differed by age (pinteraction =0·03). Thus, in participants younger than 60 years (n=1402), IGF-1 was linearly associated with a lower risk of hearing impairment (0·85, 0·73–0·99) after adjustment for age, sex, smoking, height, body-mass index, cognitive function, education, and self-reported hearing at baseline. Among participants 60 years and older, there was some evidence of a J-shaped association (pcurvature =0·02). Compared with the lowest quintile of IGF-1, ORs for quintiles 2, 3, 4, and 5 were 0·94 (0·72–1·22), 1·13 (0·86–1·48), 0·97 (0·74–1·27), and 1·24 (0·95–1·62), respectively, but associations were not statistically significant. Interpretation In people at the lower end of the older-age spectrum, there was some support for lower levels of IGF-1 being linked with hearing impairment. These results warrant replication and then testing in trials of IGF-1 supplementation. Funding The English Longitudinal Study of A