Circadian Rhythm

The suprachiasmatic nucleus synchronises to light, and every peripheral tissue — liver, muscle, gut — runs its own clock downstream. Misalignment (shift work, late-night screens, weekend social jetlag, long-haul travel) worsens insulin sensitivity, raises evening cortisol, and shifts appetite hormones. The highest-leverage fix is 10–20 minutes of outdoor light within an hour of waking, dim light after sunset, and a wake time that varies by less than 30–60 minutes across the week — including weekends.