IL6 and major depressive disorder: These sleep disorders are complex and multifactorial, with causes including pro-inflammatory cytokines (e.g., IL-6, IL-1β, TNF-α, IFN-γ), hormonal imbalances, obesity-related cytokines, dietary factors, melatonin, depression, anxiety, chronic pain, and smoking, along with medications like high-dose glucocorticosteroids.