Noise pollution has emerged as one of the leading environmental health threats globally, second only to air pollution from particulate matter in terms of burden of disease attributable to environmental risk factors (1). The increasing urbanization and industrialization have intensified noise levels in both living and working environments. In occupational settings, especially in low- and middle-income countries (LMICs), noise pollution remains a pervasive and largely under-regulated hazard. An estimated 250 million workers globally are exposed to hazardous noise levels, defined by the World Health Organization (WHO) and the Occupational Safety and Health Administration (OSHA) as exceeding 85 decibels (dB) over an 8-h time-weighted average (2). In India, studies have suggested that approximately 25% of the industrial workforce experiences exposure levels exceeding 65 dB(A), with many settings surpassing even higher thresholds (3, 4). Traditionally, occupational noise exposure has been associated with auditory effects, particularly noise-induced hearing loss (NIHL). However, a growing body of evidence now indicates that chronic exposure to high-decibel environments also results in substantial non-auditory effects. These include cardiovascular dysfunction, sleep disturbances, metabolic disorders, increased cortisol levels, impaired immune responses, and cognitive dysfunctions (5, 6). Mechanistically, noise exposure leads to activation of the hypothalamic–pituitary–adrenal (HPA) axis and the sympathetic-adrenal-medullary (SAM) system, resulting in increased secretion of stress hormones such as cortisol and adrenaline. This sustained activation can elevate blood pressure, increase heart rate, and impair cognitive performance, particularly in tasks requiring sustained attention and quick decision-making (2, 7). Despite these recognized impacts, there remains a paucity of primary research on the non-auditory effects of occupational noise in the Indian context. This gap is especially pronounced in Northeast India, a region undergoing rapid industrial growth occupational health surveillance and protective regulations. Furthermore, most existing studies are either cross-sectional or limited in sample size, failing to capture dynamic physiological changes due to acute noise exposure. In this context, the present longitudinal study aims to comprehensively evaluate the non-auditory health impacts of workplace noise exposure among industrial workers in Guwahati, Assam. Specifically, the study investigates alterations in cognitive performance using reaction time assessments, cardiovascular parameters including blood pressure and heart rate, and metabolic indicators such as blood glucose and blood cortisol levels. The study seeks to contribute to evidence-based policymaking and reinforce the need for noise mitigation strategies in Indian industrial health frameworks.

The present study employed a longitudinal observational design conducted from July 2023 to October, 2023 to evaluate acute physiological and cognitive changes associated with occupational noise exposure among industrial workers. Data collection was conducted over a four-month period, pre- and post-shift measurements were measured to assess immediate effects during a typical workday. The study was carried out in selected industrial units located in and around Guwahati, Assam. Although the broader research project includes multiple industrial sectors, the present analysis focuses specifically on chemical processing manufacturing units with similar production processes, selected to ensure comparability of noise exposure conditions and to characterize typical noise environments within this industrial category. A total of 590 adult workers aged 18–60 years participated, meeting inclusion criteria of at least 6 months of continuous employment and voluntary consent, while individuals with neurological, psychiatric, or cardiovascular disorders, or those on medications affecting cardiovascular or metabolic function, were excluded. Recruitment was facilitated through factory management, and participation was entirely voluntary. The study protocol received approval from the Institutional Ethics Committee (IEC) of AIIMS Guwahati, and all participants provided written informed consent after receiving detailed information about the objectives, procedures, and potential risks in the study.

Data collection was performed on-site within factory premises, with each participant assessed for all the mentioned parameters at the beginning and end of their 8-h shift. Ambient noise levels were measured using calibrated digital sound level meters (SLMs) mounted at shoulder height, positioned away from reflective surfaces to prevent distortion, and averaged over 15-min intervals across operational zones such as E-cutting machine areas, SRP units, cooling sections, batch rooms, and weighing areas. Ambient noise levels were measured using a calibrated digital sound level meter (Model: SIGMA SL101+; Manufacturing country: China; Serial No.: 25107797). Measurements were recorded in A-weighted decibels [dB(A)]. The instrument was operated in hand-held mode and positioned at approximately shoulder height of the workers, away from reflective surfaces, following standard occupational noise measurement guidelines. Physiological parameters, including blood pressure and heart rate, were measured at rest using validated automated sphygmomanometers after a minimum 5-min seated rest, with two readings averaged per time point. Metabolic assessments included capillary blood glucose, measured using calibrated Accu-Chek® Active glucometers, and serum cortisol, quantified via enzyme-linked immunosorbent assay (ELISA) from samples stored at −20 °C, maintaining inter and intra-assay coefficients of variation below 10%. Cognitive performance was evaluated using reaction time tests both visual and auditory administered through standardized computerized tools developed and validated in prior Indian population studies; the mean of five trials was used for analysis.

Statistical analyses were performed using SPSS version 26. Descriptive statistics were computed for all variables, and paired t-tests were applied to compare pre- and post-shift values of blood pressure, heart rate, blood glucose, cortisol, and reaction times. Statistical significance was defined as p < 0.05. To explore the relationship between noise exposure and cognitive performance, simple linear regression analyses were conducted with noise level as the independent variable and reaction time as the dependent variable, and the coefficient of determination (R²) was reported to quantify the strength of associations.

The findings from our study reaffirm that occupational noise exposure functions as a significant multi-system health hazard. While the auditory consequences of noise exposure have been widely acknowledged, our data provide compelling evidence for its acute non-auditory physiological and cognitive impacts in industrial workers. Specifically, significant post-shift elevations were observed in blood pressure, heart rate, blood cortisol, blood glucose, and reaction time performance (2, 8). The increase in systolic and diastolic blood pressure, coupled with a rise in heart rate, suggests activation of the sympathetic-adrenal-medullary (SAM) axis, likely due to noise-induced stress. Similarly, Babisch (8) and van Kempen et al. (9) documented that prolonged exposure to noise, particularly above 70 dB(A), is associated with hypertension and ischemic heart disease, especially in occupational settings. Cognitive performance, assessed using visual and auditory reaction times, showed significant associations with workplace noise exposure. Regression analyses demonstrated moderate positive associations between ambient noise levels and delayed reaction times (R² = 0.48 for visual and R² = 0.32 for auditory), indicating that higher noise levels are associated with slower cognitive responses. These findings are consistent with prior evidence linking noise exposure to impaired cognitive performance (Clark and Paunovic (10)). Blood cortisol, a well-validated biomarker of physiological stress, showed substantial post-exposure elevation in our study. This suggests heightened hypothalamic–pituitary–adrenal (HPA) axis activity, a hallmark of acute stress responses. Our findings corroborate those by Babisch (11) and Seidler et al. (12), who identified significant associations between noise exposure and elevated cortisol levels in both occupational and residential settings. A particularly novel and concerning finding was the acute rise in blood glucose levels in 22% of participants post-shift, with values exceeding 140 mg/dL. While temporary hyperglycemia may be part of an acute stress response, the observed elevations likely represent short-term stress-related metabolic responses or pre-diabetic states. Prior research has suggested that stress-mediated increases in cortisol and catecholamines may impair insulin sensitivity, leading to transient or even chronic metabolic dysregulation (13–15). There is emerging evidence that prolonged exposure to noise can increase the risk for type 2 diabetes, possibly through chronic stress pathways and circadian rhythm disruption. These findings are consistent with global evidence on the non-auditory health effects of noise exposure Basner et al. (2) and the Environmental Noise Guidelines World Health Organization (1). Our study also fills a critical evidence gap by contextualizing these effects within the Indian industrial workforce, particularly in the under-researched region of Northeast India, where baseline health data and occupational safety protocols are often lacking. The proportion-based analysis further highlighted the public health relevance of our findings. Notably, 18.5% of workers experienced a systolic blood pressure increase >20 mmHg, 12.5% had diastolic increases >10 mmHg, 28% showed heart rate elevations >15 bpm, and an alarming 71% had cortisol levels above the upper reference range. These findings are not only statistically significant but also clinically relevant, warranting immediate occupational health interventions (9, 11). Given the same-day pre-post study design, the observed changes represent acute physiological responses to occupational noise exposure and should not be interpreted as evidence of chronic or long-term cardiovascular or metabolic disease risk. While the present findings reflect acute physiological responses to occupational noise exposure, repeated exposure to similar stress responses may potentially influence homeostatic regulation over time, a hypothesis that warrants confirmation through longitudinal studies. In light of this, there is a pressing need to integrate noise monitoring into workplace health and safety frameworks (19, 20). Implementing engineering controls, enforcing regulatory compliance, and promoting worker awareness are key steps toward mitigating the non-auditory effects of noise exposure.

Occupational noise exposure in industrial settings has far-reaching health implications beyond hearing loss. This study establishes a clear association between elevated noise levels and adverse changes in blood pressure, heart rate, cognitive performance, and metabolic stress indicators. Recognizing noise as a systemic hazard mandates comprehensive workplace safety reforms.