Measures of aging tend to correlate with one another in any given study population. If someone is more affected by aging, then all of his or her physiology tends to be more functionally impacted. Thus it isn't always clear as to what can be learned from epidemiology of the sort noted here. One has to look closely at the details. Nonetheless, researchers here show that allostatic load over the course of aging correlates with the risk of suffering hearing loss. Allostatic load is a measure of stress and divergence from optimal function in the systems of the body, more or less, as determined by a range of biomarkers relating to the endocrine system, cardiovascular system, immune system, and metabolism.
Allostatic load is a cumulative measure of the physiological stressors to the body throughout the life course, reflected by damage to multiple biological systems over time. An advantage using allostatic load in predicting health outcomes, as opposed to the use of single biomarkers, is that it captures the effects of stressors on several biological systems simultaneously. Several conditions implicated with high allostatic load have associations with hearing impairment, including diabetes, obesity, sub-clinical atherosclerosis, and vascular degeneration, as have behaviours including poor diet and smoking. However, little work has been carried out into the association between inflammatory biomarkers and hearing impairment, and none (to our knowledge) on the association with allostatic load.
Data were taken from the English Longitudinal Study of Ageing (ELSA), a nationally representative study of people aged 50+ living in England over 3 time points between 2008 and 2014. Allostatic load score was comprised of thirteen different measures available at baseline and 4 years post-baseline (high-density lipoprotein/total cholesterol, triglyceride, fibrinogen, haemoglobin A1c, C-reactive protein, insulin-like growth factor 1 (IGF-1), systolic and diastolic blood pressure, mean arterial pressure, resting pulse rate, peak expiratory flow, BMI and waist circumference), measured using clinical cut-off points for normal biomarker parameters. Hearing acuity was measured with a simple handheld tone-producing device at follow-up 7 years post-baseline, while self-reported hearing impairment was measured at time point.
We included samples of 4,373 and 4,430 individuals for the cross-sectional and longitudinal analysis, respectively. In the cross-sectional model high allostatic load was associated both self-reported (odds ratio, OR = 1.08) and objective hearing loss (OR = 1.10) adjusting for age and sex. In longitudinal modelling, high allostatic load was associated with both audiometric (OR = 1.11) and self-reported hearing impairment (OR = 1.08) adjusting for age and sex. Thus prolonged high allostatic load was associated with risk of hearing impairment.