Sleep duration

Hours of sleep recorded for the night. Most trackers estimate this from movement and heart rate rather than measuring it directly.

Short sleep shifts glucose handling, blood pressure and appetite hormones within days, so it often explains a metabolic marker that moved for no other visible reason.

Consistency matters as much as the total. Read the spread across a month rather than the best or worst night in it.

Worth mentioning if you sleep a full night and still wake unrefreshed for weeks.