Up until recently, little was known about the association between noise frequency characteristics and hyperglycaemia onset.
However, in May, an article published in the Scientific Reports journal (from the publishers of the Nature journal) claimed that a breakthrough discovery had been made in relation to this relatively untouched area of human epidemiology.[i]
N.B. hyperglycaemia is the technical term for high blood glucose (blood sugar) and is the principal symptom of diabetes.[ii] Diabetes is a medical condition caused by the body’s deficient/defective production of the hormone, insulin, which prevents the body from carrying out its vital function of turning glucose into energy.
The study results were derived from a cohort of 905 volunteer employees, who worked at 4 machinery and equipment manufacturing companies for a period in excess of 1-year. Sources of high-level occupational noise exposures included metal cutting, pressing, grinding, sand blasting, polishing, and gear washing processes.
Researchers estimated the relative risk (RR) of hyperglycaemia across a range of octave band frequencies (31.5 Hz, 63 Hz, 125 Hz, 250 Hz, 500 Hz, 1 kHz, 2 kHz, 4 kHz and 8 kHz).
Overall, the participants were 80% more likely to develop hyperglycaemia if they were exposed to stimuli ≥85 dB(A), compared with those exposed to 70 dB(A).
For those exposed to peak sound pressure, hyperglycaemia risk was correlated with lower-frequency noise (excluding 4 kHz and 8 kHz). In fact, a 5 dB(A) increase in noise exposure elevated hyperglycaemia risk for all frequencies, except 2 kHz, 4 kHz and 8 kHz, with the most significant elevation in risk transpiring at 31.5Hz (27%).
Cumulative noise exposure and biological sex were also linked with increased hyperglycaemia prevalence, with women being worse affected.
Similar (albeit insignificant) observations were made in respect of diabetes.
So, how might long-term noise exposure lead to hyperglycaemia? The following metabolic pathway was proposed:
‘Repeated and chronic stimuli may cause overproduction of stress hormones (e.g., cortisol) that increase the levels of fatty acids and glucose to partially restore homeostasis. In addition, catecholamines also boost the energy supply by breaking down triacylglycerol. Such increases in stress hormones may lead to pathophysiologic alterations in blood pressure, blood lipids, blood viscosity, and blood glucose, which promote the development of hypertension, arteriosclerosis, and CVD. Because the overproduction of cortisol may inhibit pancreatic insulin secretion and reduce insulin sensitivity in the liver, skeletal muscles, and adipose tissue, it is plausible that long-term noise exposure may produce adverse changes in blood glucose’.
All in all, the authors of the paper concluded that occupational noise exposure was associated with a heightened risk of incident hyperglycaemia and that there was some evidence to imply a conceivable link between noise exposure and cardio-metabolic disease, though the biomechanical processes are not yet comprehensively understood.
They went on to boldly state that, ‘in addition to noise-induced hearing loss … the possibility of hyperglycaemia from occupational noise exposure should be considered in future studies’. This may raise some alarm bells for employers (and their liability insurers).
In order to validate, improve and build upon the present findings, a much deeper awareness of the biological processes connecting noise frequency components and hyperglycaemia is essential. Research teams may choose to recruit participants from different industrial settings and may also choose to take better account of contributing factors (sleep patterns, stress hormones, psychological factors, accurate recall of lifestyle habits, aircraft and traffic noise exposure, non-work related noise exposure, previous employment noise exposure, particulate matter/gaseous pollutant exposure, etc.), which could have skewed the relative risk ratios calculated in this latest study.
[i] Chang TY et al., Occupational noise exposure and its association with incident hyperglycaemia: a retrospective cohort study. Scientific Reports. Volume 10, Article number: 8584 (2020) <https://www.nature.com/articles/s41598-020-65646-1.pdf> accessed 9 September 2020.
[ii] ‘Hyperglycemia (High Blood Glucose)’ (American Diabetes Association) <https://www.diabetes.org/diabetes/medication-management/blood-glucose-testing-and-control/hyperglycemia> accessed 10 September 2020.