Traffic noise revs up thyroid and stress hormones in healthy adults, study finds

Traffic noise is one of the most pervasive environmental exposures of modern urban life, and its links to heart disease and metabolic disorders are well documented at the population level. What has been far less clear is what happens inside the human body during a single day of realistic noise exposure, and whether anything as simple as playing nature sounds over the top of it can blunt the damage. A randomized crossover trial now published in the Journal of Translational Medicine offers some of the most controlled human evidence to date, and its findings point to an unexpected hormonal player: the thyroid.

The study enrolled 26 healthy adults who each completed three separate 24-hour stays in a metabolic chamber. One day served as a fixed quiet reference, with ambient sound levels of roughly 46.5 dBA. On the other two days, delivered in randomized order with a 24-hour washout period between them, participants were exposed for 14 daytime hours, from 08:00 to 22:00, to either recorded traffic noise at approximately 76.2 dBA or natural-sound masking at the same equal level of 76.2 dBA. This design allowed the researchers to compare each participant against their own quiet baseline while isolating the specific effect of the noise content itself, since the masking condition matched the traffic noise in loudness but differed in character.

The measurement battery was unusually comprehensive. The researchers tracked hormones of three distinct neuroendocrine systems: the hypothalamic-pituitary-thyroid, or HPT, axis; the sympathoadrenal, or SAM, axis; and the hypothalamic-pituitary-adrenal, or HPA, axis. Alongside these they monitored cardiovascular parameters, glucose-insulin homeostasis, substrate oxidation, salivary melatonin and a series of self-reported psychological scales. All analyses used linear mixed-effects models, which are well suited to repeated-measures crossover designs because they account for the fact that each person contributes data under multiple conditions.

The headline result concerns the HPT axis, a hormonal system that regulates metabolic rate and has been virtually unexplored in noise research until now. During the traffic-noise day, thyroid-stimulating hormone rose by 0.26 µIU/mL, free thyroxine by 0.94 pmol/L and free triiodothyronine by 0.42 pmol/L, all statistically significant at P < 0.05. The sympathoadrenal axis, which governs the release of catecholamines from the adrenal medulla, was also engaged: metanephrine increased by 5.77 pg/mL and normetanephrine by 7.71 pg/mL, both significant. Notably, the classical HPA axis, the cortisol-driven stress pathway most often invoked in discussions of environmental stress, showed no measurable activation at all.

These hormonal shifts were accompanied by a cluster of early subclinical cardiometabolic changes. Heart rate climbed by 3.34 beats per minute, a highly significant effect, and diastolic blood pressure rose by 1.66 mmHg. Venous glucose increased by 0.45 mmol/L and insulin by 12.78 µIU/mL, while fat oxidation rose by 0.01 g/min. Energy expenditure showed only borderline late-day trends rather than clear elevations. Taken together, the pattern suggests that even a single day of daytime traffic noise can push multiple metabolic and cardiovascular dials in a direction associated, over longer timeframes, with elevated disease risk.

The masking intervention produced a more selective picture. When natural sounds replaced the pure traffic-noise signal at the same loudness, several of the noise-driven elevations were significantly reversed: free triiodothyronine fell by 0.27 pmol/L, free thyroxine by 0.70 pmol/L, insulin by 10.71 µIU/mL and self-reported anxiety dropped markedly. However, the sympathoadrenal catecholamine output was not measurably reduced, and the improvements in heart rate and diastolic blood pressure reached only borderline significance. In other words, masking the noise with pleasant natural sound softened some hormonal and psychological responses but did not fully normalize the body’s physiological reaction.

The authors conclude that acute daytime traffic noise triggers a selective, coordinated activation of the HPT and SAM axes without classical HPA engagement, producing early subclinical cardiometabolic alterations that include increased fat oxidation. They frame natural-sound masking as a feasible mitigation strategy for urban environments where reducing noise at its source is difficult, while cautioning that it does not erase every physiological endpoint. The trial was registered with the Chinese Clinical Trial Register under identifier ChiCTR250098645 on 12 March 2025, and the article is published open access.

Several caveats deserve emphasis. The study involved a small sample of healthy adults observed over single-day exposures in a laboratory chamber, so the findings cannot be extrapolated to people with existing cardiovascular or metabolic disease, to chronic real-world exposure, or to outcomes measured over months or years. The hormonal and cardiovascular changes, while statistically robust, were modest in absolute magnitude and their clinical significance over the long term remains to be established. What the trial does establish is a mechanistic foothold: a specific, reproducible hormonal signature through which acute noise exposure begins to reshape human metabolism within hours, and a practical, low-cost intervention that partially blunts it.

For researchers, the identification of the HPT axis as a noise-responsive system opens a new line of investigation into how environmental acoustics might influence metabolic regulation. For city dwellers, the results add to a growing body of evidence that the soundscape is not a neutral backdrop but an active physiological exposure, one that simple acoustic design choices may help to manage even when the traffic itself cannot be quieted.

Subject of Research: Acute traffic noise exposure and natural-sound masking effects on neuroendocrine and cardiometabolic responses in healthy adults

Article Title: Neuroendocrine and cardiometabolic responses to acute traffic noise and natural-sound masking in healthy adults: a randomized crossover trial

Article References: Bao, R., Xu, R., Hu, Y., Song, Y., Guo, Y., Zhu, Y., Hu, Y., Huang, Z., Ning, G., Cai, J., Wang, W., & Pan, S. (2026). Neuroendocrine and cardiometabolic responses to acute traffic noise and natural-sound masking in healthy adults: a randomized crossover trial. Journal of Translational Medicine. https://doi.org/10.1186/s12967-026-09164-0

Image Credits: AI Generated

DOI: 10.1186/s12967-026-09164-0

Keywords: traffic noise, noise pollution, hypothalamic-pituitary-thyroid axis, sympathoadrenal axis, natural-sound masking, cardiometabolic risk, randomized crossover trial, metabolic chamber, insulin, anxiety, Neuroendocrine, cardiometabolic