Sleep health is critical for psychosocial well-being and optimal physiological function (1, 2). Adults typically spend 20–40% of their day sleeping (3). Substantial epidemiological evidence indicates that sleep deficiency and disorders significantly increase the risk of cardiovascular diseases, obesity, and depression, along with other mental health conditions (4–6). It is thus imperative for public health efforts to identify modifiable factors that can improve sleep quality among older adults, particularly in light of these adverse impacts.

Household solid fuels combustion for cooking is a major source of indoor air pollution, emitting pollutants such as fine particulate matter (PM) and carbon monoxide. These pollutants degrade indoor air quality, thereby inducing systemic inflammation and oxidative stress and contributing to an estimated 4 million premature deaths annually (7, 8). In China, more than 700 million people, predominantly older adults, still rely on solid fuels for household cooking (9). Research indicates that air pollutants from such cooking practices are risk factors for coronary heart disease and increase the likelihood of non-fatal cardiovascular events (10, 11). Furthermore, a cross-sectional study of rural Chinese adults demonstrated a significantly higher prevalence of sleep disorders among solid fuel users (12). Furthermore, smaller PM particles can penetrate deep into the alveolar regions of the lungs, thereby directly interacting with pulmonary receptors and triggering systemic inflammatory responses (12, 13). Beyond the lungs, a fraction of these particles can translocate via the olfactory nerve pathway directly to the brain, constituting another pathway by which they may disrupt central nervous system functions and contribute to sleep disturbances (12, 13). These pathophysiological manifestations collectively suggest that solid cooking fuel use may impair sleep health, particularly in the elderly. However, epidemiological evidence specifically examining the relationship between exposure to different types of household solid fuels and sleep health in this population remains scarce.

Meanwhile, research interest in the relationship between dietary diversity and chronic diseases has grown. In line with previous research, dietary diversity in our study was assessed using the dietary diversity score (DDS) and the anti-inflammatory dietary diversity score (AIDDS). The DDS was designed to serve as an indicator of nutritional adequacy and a comprehensive measure of dietary patterns, as well as to capture the associated health benefits of diverse food group consumption. Evidence suggests that dietary diversity may help preserve hippocampal structure (14). A study involving 2,409 participants also reported a positive association between higher DDS and better sleep quality (15). Furthermore, several studies indicate that dietary diversity may influence sleep health in older adults through multiple pathways, such as the gut microbiota, inflammation, and oxidative stress (16–18). However, the impact of dietary diversity on sleep outcomes in the elderly remains underexplored, and it is still unclear whether dietary diversity can modify the relationship between solid fuel use and sleep health.

To investigate the potential associations between these factors and sleep health, we analyzed data from the Chinese Longitudinal Healthy Longevity Survey (CLHLS) to evaluate the relationships between household exposure to solid fuel use for cooking, adherence to dietary diversity, and sleep health in the elderly population.

In this nationwide study of Chinese older adults, exposure to solid cooking fuels was significantly associated with poor self-reported sleep quality. In contrast, higher DDS/AIDDS were associated with better self-reported sleep quality and adequate sleep duration. Notably, higher dietary diversity appeared to attenuate the adverse association between solid fuel use and poor self-reported sleep quality.

Currently, evidence on the association between exposure to solid cooking fuels and sleep health remains limited. Only three studies have explored this link. For instance, a case–control study involving 1,616 Chinese participants over the 80 years of age reported an association between solid fuel use and poor sleep quality (29). A study from the China Kadoorie Biobank prospective cohort, included 283,170 rural participants and demonstrated an association between solid cooking fuel use and sleep disturbance (30). In addition, a research conducted in rural Henan, China, reported a positive association between solid cooking fuel use and poor sleep quality (12). Our findings were consistent with these studies and provide further evidence that exposure to solid cooking fuels was correlated with poor self-reported sleep quality among older adults. The underlying mechanism of this association involves exposure to particulate matter (PM)_2.5 generated by incomplete combustion of solid fuels, which may reduce serotonergic neurotransmission and disrupt circadian rhythms, thereby contributing to daytime sleepiness and impaired nighttime sleep in the elderly (31). Furthermore, pollutants from solid fuels can impair pulmonary function, exacerbate respiratory symptoms, or induce neuroinflammation, all of which were potential pathways to sleep disturbances (32, 33). Meanwhile, pollutants from solid fuels may induce neural damage by altering blood–brain barrier integrity and promoting cortical neuron degeneration, which could ultimately impair brain function and disrupt sleep architecture. These effects were likely to be more pronounced in elderly populations experiencing age-related declines in cerebral function (29, 34). Interestingly, analyses of specific fuel types revealed that only the use of wood or straw was significantly associated with poor self-reported sleep quality compared to clean fuels (OR = 0.85, 95%CI = 0.76–0.94), whereas no significant associations were found for coal/coke or charcoal. This underscores the particularly detrimental impact of biomass fuels like wood and straw. Consequently, future public health policies should prioritize phasing out these highly polluting fuels, especially among vulnerable populations. While a full transition to clean energy remains the ultimate goal, implementing feasible interim solutions-such as improving ventilation and promoting efficient cookstoves-was of more immediate practical significance. It should be noted that the non-significant findings for coal/coke and charcoal should be interpreted with caution due to the small sample size (N < 300), which limited the statistical power and increases the possibility of chance findings. Therefore, large-scale, multi-center prospective studies were warranted to confirm these relationships.

Consistent with the only published study to date (15), our study also identified an association between a higher DDS and better self-reported sleep quality and adequate sleep duration. Furthermore, we also reported a significant link between a higher AIDDS and better self-reported sleep quality and adequate sleep duration among older adults. These findings suggest that adopting a diverse and anti-inflammatory diet rich in fruits, vegetables, legumes, and tea may help prevent sleep disturbances in older adults. The underlying mechanism may be that such a diet provides abundant anti-inflammatory and antioxidant compounds, which can mitigate systemic inflammation and oxidative stress, thereby improving sleep (16, 17). Furthermore, dietary diversity may influence sleep through the gut microbiota, which plays a critical role in sleep regulation (18). A varied diet can promote a favorable gut microbiome by increasing the abundance of beneficial bacteria, thereby potentially supporting healthier sleep patterns (35, 36). Therefore, the association between dietary diversity and sleep health were likely underpinned by multifaceted mechanisms, potentially involving nutrient synergy, anti-inflammatory effects, gut microbiota interactions, and reduced oxidative stress. Further experimental studies were warranted to elucidate the precise biological pathways involved. Although direct evidence linking DDS/AIDDS to sleep health was limited, these scores have been consistently associated with broader health benefits. For instance, higher DDS has been linked to reduced all-cause mortality and lower incidence of type 2 diabetes in Anglo-American cohorts (37), a 5% lower risk of dementia in a UK population (38), and a lower prevalence of metabolic syndrome in Japan (39). This established role of dietary diversity in promoting overall health provides a valuable context for interpreting its potential benefits on sleep.

Our study found a null association between solid fuel use and sleep duration in both the main and subgroup analyses. One possible explanation was that sleep duration in this study was determined by the question, “How many hours do you sleep per day?” This measure does not distinguish whether the reported sleep duration includes daytime napping. Therefore, it may fail to capture potential compensatory sleep behaviors, which could contribute to the observed null association. Additionally, we observed that solid fuel use appeared to be associated with inappropriate sleep duration in model 1 and model 2, but this association disappeared in the fully adjusted model. This suggests that, after adjusting for chronic diseases, residence, lifestyle, and occupation, the association between solid fuel use and sleep duration appears to be mediated through related determinants like the need to wake up early for strenuous work. Any remaining direct effect of solid fuel use may be too weak to significantly alter total sleep duration. Thus, the adverse impacts of solid fuel use may manifest more precisely in sleep quality than in sleep duration. Further research is necessary to confirm these findings and to inform more targeted public health interventions.

Notably, our joint-effect analysis revealed that the combination of clean cooking fuels and a higher DDS/AIDDS was associated with better self-reported sleep quality and sleep duration, and a significant interaction was detected (P _interaction < 0.05). This protective effect may be explained by the anti-inflammatory and antioxidant properties of a diverse diet (40), which could counteract the systemic inflammation and oxidative stress induced by solid fuel emissions, thereby mitigating their adverse effects on sleep (41, 42). Furthermore, a diverse diet provides an array of nutrients (e.g., vitamins C and E, minerals, polyphenols) that can directly neutralize free radicals generated from PM_2.5 exposure, thereby alleviating oxidative damage (43, 44). Our findings demonstrate that high dietary diversity can substantially mitigate the adverse effects of solid fuel use on sleep. Therefore, promoting dietary diversity represents a viable nutritional intervention strategy to protect sleep health, especially for vulnerable populations in regions where a rapid transition to clean fuels was not immediately feasible. However, due to the inherent limitations of the study, further research on causal relationships is necessary to validate our findings.

Our study represents, to our knowledge, the first investigation into the association between solid cooking fuel exposure and sleep health and the potential moderating role of dietary diversity. Major strengths include the large, nationally representative sample and the robustness of the findings across sensitivity and subgroup analyses.

This study has several limitations. First, the cross-sectional design precludes the establishment of causal relationships between dietary diversity, household fuel use, and sleep outcomes. Furthermore, we cannot rule out the possibility of reverse causality. For instance, poor sleep patterns may themselves influence choices regarding cooking fuels or dietary habits. This potential bidirectional relationship could have affected the observed associations and must be considered when interpreting our findings. Second, the self-reported data on exposure and outcomes were susceptible to recall bias, although face-to-face interviews by trained staff may have mitigated this. Third, the use of different frequency thresholds (“often” for fruits and vegetables vs. “weekly” for other foods) to define habitual consumption in our study may affect the internal consistency and comparability of the DDS. Future research would benefit from adopting a more uniform standard for defining dietary frequency. Fourth, the findings from Chinese older adults may not be generalizable to other populations. Future longitudinal studies across diverse populations are needed. Finally, despite adjusting for numerous confounders, residual confounding (e.g., by unmeasured environmental factors) remains possible, although E-value analysis suggested that substantial unmeasured confounding would be needed to nullify the observed associations.

In this national study of Chinese older adults, exposure to solid cooking fuels was associated with poor self-reported sleep quality, while higher DDS/AIDDS were associated with both better self-reported sleep quality and adequate sleep duration. Notably, high dietary diversity appeared to mitigate the adverse association between solid fuel use and sleep health. These results highlight the potential of dietary interventions and underscore the need for further research to confirm causality and elucidate mechanisms.