In the present study, the relation between adherence to a pro-inflammatory diet and lifestyle, reflected by DLIS, and mental health and sleep quality were investigated in a multicenter cross-sectional study of Iranian maintenance HD patients. The results revealed that there was a significant association between high DLIS and having poor sleep quality and mental health disorders including stress, anxiety, and depression among HD patients.
Sleep disturbances are frequent consequences of ESRD and are a major cause of death and deterioration in these patients' quality of life (2). Numerous factors can impact sleep hygiene, including age, gender, comorbidities, anemia, uremic pruritus, and the length of dialysis treatment (27). However, previous research has indicated that diet and lifestyle are also important sleep hygiene predictors. It has been found that older adults who have a Mediterranean diet, which is regarded as a healthy eating pattern, have better sleep hygiene (28). A cross-sectional study consisting of 741 maintenance HD patients also indicated that a higher intake of dietary fiber in vegetables could enhance the quality of sleep (29). Jansen et al. in a cohort study with 4467 Mexican women, showed that participants in the highest quartiles of the modern Mexican pattern (tortillas and soda, along with low fiber and dairy products) had a 23% higher likelihood of having poor sleep quality compared to those in the lowest quartile (30). Due to concerns about phosphorus and potassium, HD patients are required to undergo significant lifestyle changes, including adhering to a typical renal diet limited to vegetables, fruits, nuts, legumes, dairy, and whole grains (31). Therefore, unhealthy eating habits may be more common in HD patients, and these habits can be related to poor sleep hygiene.
In the current study, more than 60.5% of hemodialysis patients had poor sleep quality. This study showed that after controlling for potential confounders, HD patients with a pro-inflammatory diet and lifestyle were more likely to experience poor sleep quality. Our findings are consistent with other research that has demonstrated positive correlations between a pro-inflammatory diet indicated by higher scores of the dietary inflammatory index (DII), and short sleep duration, sleep disturbances, poor sleep quality, higher wake-after-sleep onset, and dysfunction during the day (32–35). Notably, the DIS is a novel dietary inflammatory index that may offer benefits over the DII; the DII mostly comprises certain anti/pro-inflammatory nutrients, and may not take into account other dietary components in foods, that can cause inflammation. Also, the DII mostly does not consider the impacts of nutrient interactions. Furthermore, in three populations, the DIS was found to have a stronger direct correlation with the circulating levels of inflammatory markers than the DII and Empirical Dietary Inflammatory Pattern (EDIP) (36). Moreover, previous studies have indicated that the lifestyle-related components of LIS, such as smoking, BMI, and physical activity, may also have a significant impact on metabolic homeostasis and inflammatory state. According to a population-based cohort study, a higher inflammatory potential of lifestyle, measured by the higher score LIS, was associated with an increased incidence of CKD in Iranian adults (37). Since the LIS only contains lifestyle and non-dietary components and the DIS only focuses on diet, we employed the combined DLIS index (16), which is a more comprehensive index that includes both dietary and non-dietary elements. Recent studies have demonstrated a clear correlation between the DLIS and the risk of developing chronic illnesses associated with systemic low grade inflammation such as metabolic syndrome and insulin resistance (38, 39). Currently, there is growing evidence that inflammatory factors and sleep quality are significantly associated.
The biological mechanisms underlying the relationship between dietary and lifestyle factors and the quality of sleep may include the regulation of sleep by inflammatory peptides (40), neuroendocrine and autonomic pathways connecting sleep to the immune system, and cytokine responses (41). It has been previously documented that inflammatory status and metabolic homeostasis may be significantly impacted by lifestyle factors such as physical activity, BMI, and smoking. Increased adipose tissue and a raised BMI are significantly correlated with pro-inflammatory biomarkers (adipokines, TNF-α, CRP, and interleukin-6) and systemic chronic inflammation (42), which in turn can cause poor sleep quality. It is reported that higher BMI is associated with a poor quality of sleep in young adults. However, some cross-sectional studies have not discovered any correlation between obesity as an inflammatory condition and diet-induced inflammation as evaluated by DII or EDII (43, 44). The differences between our results and the results showing no association could be attributed to variations in the population, the study design, the assessed food items, the dietary indices (like the DII, which emphasizes nutrients rather than food groups), the tools used to assess dietary intake, and the influence of unmeasurable confounding factors.
Another key lifestyle component that has demonstrated promise in terms of bettering overall sleep quality, reducing sleep latency, and improving sleep quality is physical activity (45). Nonetheless, studies have revealed that HD patients, for various reasons, are less physically active than healthy age-matched controls. Through a comprehensive analysis of 23 articles, a systematic review study discovered a favorable correlation between physical exercise and sleep quality across various demographic categories (46). Several processes can explain the relationship between physical activity and better sleep, such as the release of endorphins, which can reduce stress and anxiety and improve relaxation and sleep quality, circadian rhythm regulation, and increase anti-inflammatory cytokines production (47). Furthermore, a population-based study including 26,282 Chinese people revealed that smokers experienced far worse sleep quality and disruptions from their sleep compared to nonsmokers (48). Smoking negatively affects metabolism, β-cell dysfunction, and IR, which are mostly caused by an increase in inflammatory biomarkers and cytokines such as CRP (49).
Our research also suggested that a lifestyle and dietary pattern with more pro-inflammatory qualities may be associated with an increased risk of mental health issues. Our results indicate that in our HD population, the prevalence of depression, anxiety, and stress was 53.7%, 53.0% and 47.3%, respectively. A study conducted by Palmer et al. involving an observational sample of 55,982 individuals with CKD revealed that approximately 25% of these patients experienced depression, and those with HD were at an increased risk (50). The association between single components of the DLIS and mental health disorders has been also investigated in previous research. A large body of research supports the link between mental problems and diet quality. The risk of depression and anxiety in Iranian adults was found to be negatively correlated with their adherence to the healthy eating index (51). A 2021 meta-analysis looked at the relationship between dietary potential for inflammation and mental health among 92,242 men and women from Asia, Europe, America, and Australia. The findings indicated that there is a substantial correlation between symptoms of depression, anxiety, and distress and a more inflammatory diet, as measured by the DII (52). However, in a cross-sectional study involving 400 health professionals conducted by Rostami et al., no significant associations were found between adherence to the Mediterranean-DASH Intervention for Neurodegenerative Delay (MIND) diet as an anti-inflammatory dietary pattern and odds of stress, anxiety, and depression either in the crude or multivariable-adjusted models (53). The study's conclusions may apply to only a small group of populations, male health professions, and might not be generalizable to females or other populations. Furthermore, the study's results were evaluated by self-reported questionnaires, which raises the possibility of recall bias and misreporting.
Nevertheless, it is still unclear what precise biological process leads to depression or other mental illnesses. A growing body of evidence suggests that systemic inflammation, as indicated by high levels of CRP, may be a significant contributor to mental health problems like depression and anxiety (54). There is two-way comorbidity between inflammation and mental illness, meaning that increased inflammation of the body is associated with an increased risk of mental problems (such as depression), and depression itself is associated with increased behaviors that trigger inflammation, such as unhealthy eating habits (55). A comprehensive meta-analysis examining the contributions of main modifiable lifestyle factors to the prevention and treatment of mental disorders revealed that smoking is a causal factor of both common and severe mental illness, while physical activity protects against some mental disorders (56). Additionally, using data from the population-wide Austrian registry, obesity was found to be a significant risk factor for obtaining additional mental health diagnoses at every decade of adulthood, highlighting the significance of obesity as a pleiotropic promotor of health problems (57).
The strength of the current study is that it is the first to examine the relationship between DLIS and sleep quality and mental health conditions in HD patients. Furthermore, our study includes a relatively large sample size from eight different hemodialysis centers in three cities with a variety of dietary and lifestyle habits. In-person interviews with participants were conducted using valid questionnaires to gather information on their dietary intakes and level of physical exercise. However, the current study had some limitations. The weights assigned to the DIS and LIS have been verified for the US population; they might not be suitable for other populations. Secondly, the reliance on self-reported measures for assessing sleep quality and mental health conditions may introduce response and recall bias. Some items were excluded in the calculation of DIS and LIS. The final DIS was calculated using 18 instead of 19 items and 3 instead of 4 for LIS.