What makes some people natural deep sleepers?

Some people are naturally deep sleepers due to a combination of genetics, brain chemistry, and physiology. Research has identified specific gene variants, including mutations in the ADRB1 gene and others affecting circadian rhythms, that influence sleep depth and duration. These genes affect how the brain cycles through sleep stages, particularly slow-wave sleep, which is the deepest and most restorative phase. Neurologically, deep sleepers tend to produce more sleep spindles, which are bursts of brain activity during non-REM sleep that essentially act as a shield against external disturbances. Age, fitness level, and overall health also play roles, as younger people and those in good cardiovascular shape often experience more slow-wave sleep naturally.