When music matters: how music app use buffers the relationship between boredom proneness, loneliness and Internet Gaming Disorder.

Chronic diseases are a major threat to the life and health of older adults. Multimorbidity—the coexistence of two or more chronic conditions—afflicts the majority of older adults and markedly impairs physical and mental function, quality of life, and survival. Against the backdrop of rapid population ageing, the number of older adults living with multimorbidity is steadily increasing (). The high prevalence of chronic illness exposes older people to persistent somatic pain; more than two-thirds report persistent pain complaints (). Somatic pain is an unpleasant bodily sensation linked to tissue damage, and chronic-disease complications can intensify pain in multiple body regions (). Individuals suffering from pain frequently experience sleep disturbances—shortened sleep duration, reduced sleep quality, and insomnia (, ). Evidence indicates that the likelihood of sleep problems among people in pain is up to 70% higher than among their pain-free counterparts (). Prolonged pain not only curtails sleep but may also contribute to systemic inflammation and hypothalamic-pituitary-adrenal (HPA) axis hyperactivity (, ), and disturbs serotonin and norepinephrine metabolism, key regulators of sleep and mood (, ). These physiological changes jointly disrupt the sleep-wake cycle and further induce negative emotional states (). Globally, more than 50% of patients with chronic pain exhibit depressive symptoms (). Depression in later life undermines appetite, lowers mood, fuels anxiety, and increases suicide risk (). In primary care, chronic pain is one of the most demanding long-term conditions in terms of consultation rates and costs (). To date, most studies have examined pairwise links among chronic disease, pain, and depression, leaving the interrelationship among all three underexplored. In particular, whether somatic pain and sleep duration mediate the association between chronic disease burden and depressive symptoms remains insufficiently investigated. Based on pathophysiological evidence, we propose a chain mediation model: chronic disease count (X) is associated with greater somatic pain (M1), which is associated with shorter sleep duration (M2), and both M1 and M2 are associated with higher depressive symptoms (Y). This temporal sequence is clinically plausible because chronic diseases are long-standing conditions that predispose to pain, which in turn disrupts sleep and mood (, ). We hypothesize that: (1) chronic disease count is directly associated with depressive symptoms; (2) somatic pain independently mediates this association; (3) sleep duration independently mediates this association; and (4) somatic pain and sleep duration form a sequential (chain) mediating pathway (). By testing this model, we seek to elucidate the intrinsic mechanisms underlying the clustering of health problems in later life and provide a theoretical basis for integrated geriatric care.