How strong is the evidence for Sleep Quality?

The evidence base for this topic is comparatively weak and diffuse: available studies address related but distinct subjects, such as loneliness and sleep, herbal supplements (ashwagandha, lemon balm) and psychological well-being, and gut-brain-axis nutrition, none of which directly test structured interventions to improve sleep quality itself. That evidence is currently rated moderate (50/100), built on 4 published studies, including 1 randomized controlled trial and 3 meta-analyses -- a reasonable base, but not yet enough for full certainty.