This cross-sectional study is the baseline survey of the Seafarers Health Cohort of China, which is an ongoing large-scale health surveillance cohort aiming to promote physical and mental health among seafarers in China.

Participants were recruited from March to May 2024 in collaboration with the China Shipowners’ Association (CSA). As a national authoritative maritime industry organization, the CSA consists of nearly 400 domestic and international member entities, including shipowners, shipping operators, vessel managers, as well as shipping insurance, financial institutions, maritime research institutes, and universities. Its member enterprises account for more than 85% of China’s national maritime transport capacity. This membership system encompasses both national leading shipping conglomerates and numerous local professional maritime service institutions.

Considering seafarers’ frequent cross-regional mobility and irregular work schedules, all recruitment and data collection procedures were conducted online using a structured electronic questionnaire hosted on the Wenjuanxing survey platform [17]. This allowed participants to complete the survey either on board or on shore leave, without geographical constraints. A standardized, multistage recruitment procedure was followed across all participating institutions. The research team developed a unified study protocol and the electronic questionnaire. The questionnaire link and recruitment notice were distributed by the CSA through its official communication channels to the designated contacts at each participating enterprise. The coordinators were then responsible for forwarding the survey invitation to all active seafarers within their respective companies. The recruitment strategy covered all occupational ranks and departments, with no artificial screening or selective exclusion. All eligible seafarers accessed the survey voluntarily and completed it independently, free from managerial supervision or external interference. Participants were informed of their right to decline or withdraw from the survey at any time.

Several exclusion criteria were applied to the final analytical sample. Participants with preexisting hepatic conditions were excluded, including viral hepatitis (hepatitis B, C, etc), drug-induced liver injury, autoimmune liver diseases, and inherited metabolic liver disorders. Female seafarers accounted for merely 0.85% (n=70) of the original sample and were excluded from formal analyses due to extremely limited sample size. The characteristic comparisons between excluded female seafarers and included male seafarers are presented in Table S2 (Multimedia Appendix 1). Additionally, participants with missing BMI records were also excluded (Figure S1 in Multimedia Appendix 1).

This study was approved by the Institutional Review Board of Ruijin Hospital (approval number: 2023248). Written informed consent was obtained from all study participants before enrollment. Prior to data analyses, complete anonymization of all study datasets was performed to protect participants’ privacy and maintain information confidentiality. No financial remuneration was offered to participants for their involvement in this research. In addition, none of the images and figures in the manuscript and supplementary materials contains any information that could identify individual participants.

Descriptive characteristics of seafarers were described as mean (SD) or median (IQR) for continuous variables and numbers and percentages for categorical variables. The Student t test and Kruskal-Wallis tests were used for continuous variables, and χ² test was used for categorical variables in comparing characteristics differences between the groups, as appropriate. Harman’s single-factor test incorporating all 123 questionnaire items was conducted to assess common method bias. The first factor accounted for 19.94% of the total variance, which fell below the 40% threshold, indicating that common method bias was unlikely to be a major concern (Table S1 in Multimedia Appendix 1).

The prevalence of NAFLD was estimated across strata by demographic characteristics, lifestyle factors, occupational characteristics, comorbidity, noise exposure, as well as perceived impact of noise. To explore the associations of noise exposure and perceived noise impact with NAFLD, we performed a series of age-adjusted and fully adjusted logistic regression, calculating odds ratios (ORs) and 95% CIs. Next, we estimated the prevalence, ORs, and 95% CIs of NAFLD stratified by noise exposure and BMI, as well as by perceived noise impact and BMI. In addition, we explored the combined associations of noise exposure and perceived noise impact with NAFLD and further examined these combined associations stratified by noise levels at different locations (workplace and rest areas). Multiplicative interactions between noise exposure, location-specific noise levels, and perceived noise impact were tested by including product terms in the regression models, and the corresponding interaction P values were calculated. All models were adjusted for age, educational level, marital status, household registration, smoking status, physical activity, dietary habits, shift work, monthly income, sleep duration, hypertension, dyslipidemia, DM/IGT, and BMI as a continuous variable.

To assess the robustness of our findings, we conducted sensitivity analyses excluding participants with hearing loss and reestimated both the independent and combined associations. All analyses were performed using Stata (Stata Corporation). A 2-tailed P value of <.05 was considered to be statistically significant.

A total of 8143 male seafarers were included in the final analysis, with a median age of 39 (IQR 33‐49) years. Over half (n=4868, 59.8%) of the participants had a BMI of 24.0 kg/m² or above. The demographic characteristics of the study population are presented in Table 1. Compared with those without NAFLD, individuals with NAFLD tended to be older and more likely to be married, and had higher proportions of smoking, frequent alcohol consumption, and lack of regular exercise. They also tended to have shorter sleep duration. Participants with NAFLD also had significantly higher prevalence of hypertension, dyslipidemia, and DM/IGT (all P<.001). Notably, the proportions of overweight or obesity, exposure to chronic workplace noise, and high perceived noise impact were significantly higher among individuals with NAFLD. The distributions of various noise exposure types and perceived noise impact are illustrated in Figures S2 to S4 (Multimedia Appendix 1).

To examine the robustness of our findings, we performed sensitivity analysis by excluding participants with self-reported hearing loss. The associations of chronic noise exposure and perceived noise impact with NAFLD across BMI strata (Tables S5-S6 in Multimedia Appendix 1) remained materially unchanged, confirming the stability of our results.

This is the first large-scale study to estimate the prevalence of NAFLD and its associations with noise exposure, perceived noise impact, and BMI among seafarers. It not only fills a critical gap in maritime occupational noise-related metabolic health research, but also highlights an urgent need for targeted NAFLD prevention strategies to mitigate liver damage in 2.03 million Chinese seafarers and global seafarers more broadly [21]. The overall prevalence of NAFLD among 8143 Chinese seafarers was 18.5% (n=1503), with higher prevalence observed in those with a BMI of 24.0 kg/m² or above, chronic noise exposure, and higher perceived noise impact (Textbox 1). The combined association of chronic noise exposure and perceived noise impact with NAFLD was only observed among individuals with a BMI of 24.0 kg/m² or above. Furthermore, a significant interaction between resting-area noise levels and perceived noise impact in relation to NAFLD was identified specifically in the overweight and obese subgroup.

The prevalence of NAFLD in this study was significantly lower than that reported in the general Chinese population in 2 previous studies (36.7% and 23.6%) [22,23]. This difference is partly attributable to the predominantly manual labor roles of seafarers, which result in higher levels of habitual physical activity compared to the largely sedentary general population. Additionally, the occupational demands of seafaring impose higher physical fitness requirements, necessitating preemployment medical screening. This selection process likely contributes to a “healthy worker effect,” leading to a higher baseline level of health within this occupational group. As seafaring is a strenuous occupation with rigorous physical fitness criteria, only physically qualified individuals can sustain active sea service, rendering currently employed seafarers generally healthier than the general population. Additionally, NAFLD prevalence increases progressively with age. While our study population was predominantly composed of young and middle-aged seafarers, with individuals aged 55 years or above accounting for merely 6.9% (n=563) of the total sample. This relatively young age distribution may further partially explain the lower NAFLD prevalence observed in the present seafarer population.

Previous studies have confirmed that overweight and obesity act as the core pathological basis of NAFLD through triggering insulin resistance and ectopic fat deposition [24,25]. While our study suggests that the noise exposure may synergistically exacerbate NAFLD pathogenesis alongside obesity-related metabolic disorders. As obesity inherently disrupts insulin sensitivity and promotes ectopic lipid accumulation, concurrent noise exposure might amplify hepatic lipid metabolic disturbances via the HPA axis. This pathway elevates circulating cortisol and stimulates sympathetic nerve activity, jointly accelerating the progression of NAFLD [26].

Several studies have reported associations between occupational noise exposure and lipid metabolic disorders, yet direct evidence linking noise exposure to NAFLD, and its combined effects with obesity, remains limited. Studies based on Chinese public institutions and corporate workers, as well as the general US population, have documented a significant association between noise exposure and elevated BMI [27,28]. A previous study involving 4672 male automotive manufacturing workers reported that individuals with cumulative noise exposure of 95 dB(A) or above had a 39% increased risk of NAFLD [29]. Chronic noise exposure may activate the HPA axis, resulting in elevated glucocorticoid levels [8]. Glucocorticoids in turn promote hepatic lipid accumulation by stimulating adipose tissue lipolysis and hepatic de novo lipogenesis, while simultaneously reducing hepatic fatty acid β-oxidation [30], thereby favoring the development of NAFLD.

Interestingly, we observed that higher perceived noise impact was significantly associated with a higher prevalence of NAFLD. Perceived noise impact can be conceptualized as a phenotypic expression of psychological stress in response to environmental noise. It arises from the combined influence of noise stimuli and personal traits and is positively associated with noise sensitivity [31,32]. The positive relationship between perceived noise impact and NAFLD might also be mediated by the chronic HPA axis stress pathway. Long-term perceived noise disturbance may elicit negative emotions and psychological annoyance, thereby activating the HPA axis and promoting excessive cortisol secretion. Previous acoustic research has shown that individuals with high perceived noise exposure report significantly higher levels of negative emotions and remain in a sustained stress state [31], which provides theoretical support for the mechanistic hypothesis of this study. However, given the cross-sectional design of this study, the observed association between perceived noise impact and NAFLD cannot rule out reverse causality; that is, individuals with preexisting NAFLD may be more vulnerable to perceived noise disturbance. To date, some studies have reported a positive association between NAFLD and anxiety, and further targeted research on this topic is warranted.

This study is also the first to investigate the combined associations of chronic noise exposure and perceived noise impact with NAFLD. We found that NAFLD risk was significantly elevated among individuals who reported higher perceived noise impact in relatively quiet environments, or who had both chronic noise exposure and perceived noise impact. This suggests that perceived noise impact may operate independently of noise exposure. Accordingly, environmental noise reduction alone is insufficient to protect this population; psychological stress alleviation and acoustic environment optimization are also needed. Notably, perceived noise impact was significantly associated with higher risk of NAFLD regardless of whether the workplace or living quarters were reported as noisy, underscoring its importance as a psychological stress indicator. In resting areas, even when perceived noise impact was rated as “no effect,” NAFLD risk remained significantly elevated, possibly because metabolic regulation is more vulnerable during rest periods, and residential noise may still disturb metabolic homeostasis with little subjective awareness. Furthermore, a significant multiplicative interaction between noise exposure and perceived noise impact in resting areas suggests that noise-related psychological stress is a key driver of NAFLD.

These associations were observed exclusively among overweight or obese individuals, indicating that this population is more vulnerable to noise-induced stress, which may disrupt hepatic lipid metabolism through chronic stress pathways. Notably, clinical research further supports this biological rationale: body fat distribution and cortisol clearance jointly modulate the association between NAFLD and insulin sensitivity, and higher cortisol clearance is independently associated with reduced insulin sensitivity regardless of BMI [33].

Given that noise-induced psychological stress contributes to metabolic dysfunction, lifestyle interventions that relieve stress and improve metabolism may mitigate NAFLD risk. Currently, physical activities, such as yoga and mindfulness meditation, not only exert positive effects on mood regulation but also contribute to the improvement of inflammation and metabolic status [34,35]. Consistent with this, our study found that regular physical activity and a healthy diet were both significantly associated with a lower prevalence of NAFLD. All the above findings confirm that a healthy lifestyle may effectively improve health simultaneously through multiple pathways.

This study highlighted the importance of corresponding public health interventions for seafarers. The onboard acoustic environment can be improved by renovating living quarters, reducing mechanical equipment noise, and developing and deploying advanced noise-protection equipment for seafarers. Beyond physical noise control, targeted support for crew members is also critical, such as reasonable shift planning to secure adequate rest and avoid cumulative noise-triggered psychological stress, psychological counseling services, and regular recreational activities. Shipping companies should also establish integrated occupational health management systems featuring routine health education, specialized physical examinations, and personalized intervention programs to sustain seafarers’ physical and mental health.

Several limitations should be considered when interpreting the findings of this study. First, noise exposure was assessed via self-reported measures rather than objective personal dosimetry. While self-reported noise exposure assessment is a practical approach for large-scale epidemiological surveys and has been shown to correlate reasonably well with objective instrumental measurements in previous validation studies, it does not allow for precise quantification of the actual decibel levels experienced by individual seafarers. Second, detailed data on the use of hearing protection devices (HPDs) were not collected. The use of HPDs could attenuate the actual noise exposure intensity and thus may influence the observed effect estimates. Nevertheless, self-perceived noise exposure—even with HPD use—may still reflect the actual exposure level in the current occupational setting and may capture the association with the outcome of interest [36]. However, the absence of both objective dosimetry and HPD usage data in the present study limits our ability to directly compare our findings with quantitative exposure-response relationships reported in the literature. Future investigations incorporating objective noise dosimetry and detailed HPD usage records are needed to more precisely describe the association between occupational noise exposure and NAFLD among seafarers. Third, as seafarers self-reported their fatty liver findings from routine check-ups, which may introduce information bias. Participants might underreport fatty liver due to poor memory or stigma, or alternatively over-attribute liver abnormalities to occupational stress. Although multivariate adjustment for highly comorbid metabolic disorders was performed, it cannot correct for recall errors directly. However, the questionnaire did not explicitly implicate a causal link between noise exposure and liver disease, reducing the likelihood of systematic overreporting driven by participant expectations. We additionally conducted a sensitivity analysis excluding participants with self-reported hearing loss—a subgroup potentially more attentive to noise-related health effects—and found that the ORs, effect directions, and statistical significance of the noise-NAFLD associations were consistent with the primary analysis, suggesting that reporting bias did not materially alter our main findings. Nevertheless, in the absence of objective clinical gold-standard verification or individual-level Kappa concordance tests against medical records, residual recall bias cannot be entirely ruled out. Fourth, the nature of the cross-sectional study design limits its capacity to establish causality. In addition, the sample only comprises Chinese male seafarers. Female participants only accounted for only 0.85% (n=70) of the original sample, consistent with the 1% share of female maritime workers reported in the 2024 survey by the International Maritime Organization and the Women’s International Shipping & Trading Association [37]. Therefore, the results cannot be generalized to female seafarers. Finally, the generalizability of our findings to other populations or occupational settings should be interpreted with caution, as offshore working conditions and living environments differ substantially from land-based jobs.

In conclusion, this study suggests that chronic noise exposure and perceived noise impact are significantly associated with elevated NAFLD risk among seafarers, particularly individuals with a BMI higher than 24.0 kg/m². The combined associations of chronic noise exposure and perceived noise impact highlight the potential role of environmental and psychological factors in NAFLD. Longitudinal studies are warranted to confirm these associations.