BMI over the life course and hearing ability at age 45 years: a population-based cohort study
Previous research on anthropometric factors and adult hearing loss has found relationships, in separate studies, to birthweight and contemporary BMI. However no study has examined data on BMI over the life course. This paper uses data from the 1958 British Birth Cohort to examine relationships between BMI (both in childhood and adulthood), changes in BMI between adjacent age waves, and hearing thresholds at 1 kHz and 4 kHz obtained by audiometric examination at age 45 yrs. Body Mass Index (BMI) in adulthood, but not in childhood, was associated with increased hearing threshold levels at both 1 kHz and 4 kHz at age 45 yrs. Two further models examine the effect of changes in BMI between successive waves and adult hearing thresholds, firstly adjusting for childhood hearing loss and a range of further childhood factors (including birthweight, family history of hearing loss, mother’s weight, childhood social class) and secondly adjusting in addition for noise, current social class, current systolic blood pressure and diabetes, current smoking and drinking. In the first model, increases in BMI at age intervals throughout the life course, over both childhood and adulthood, were independently associated with increased hearing threshold levels at both frequencies in mid-life, largest relationships being shown at both frequencies to increasing BMI in adolescence and in early adulthood. These relationships generally persisted in the second model, though were reduced more at earlier ages (pre 23 yrs). Noise at work attenuates the relationship between BMI change and mid-life hearing threshold, more so at 4 kHz than at 1 kHz and for BMI change at older ages. The relationship between 1 standard deviation of BMI change between 11 and 16 years, and mid-life hearing threshold was close to one-third that of noise at work (>5yrs vs. none). Future studies should be carried out to determine the mechanisms underlying these relationships and whether these relationships strengthen as the cohort ages further.