How strong is the evidence for Sleep Duration?

Sleep duration and mortality risk is one of the more extensively meta-analyzed relationships in sleep research, with multiple independent meta-analyses of prospective cohorts consistently finding a U-shaped relationship: both short and long habitual sleep are associated with higher all-cause and cardiovascular mortality compared to moderate durations. That evidence is currently rated strong (80/100), built on 6 published studies, including 2 meta-analyses -- enough for real confidence in the effect.