Persistently high levels of the hormone cortisol reduce the body's ability to release stored fat and lead to elevated cortisol levels at night, which interferes with uninterrupted sleep.

When your body doesn't make enough cortisol, insulin can drop your blood sugar too much at night, which might wake you up.

When healthy young men don't get enough sleep for a few nights, their stress hormone (cortisol) actually goes down—but their blood sugar control gets worse. This suggests that something other than stress hormones is causing the metabolic problems.

Staying awake all at once doesn't actually change your stress hormones, blood pressure, or heart rate the next day if you're a healthy young adult in a relaxed setting. This means that just losing a night of sleep won't automatically spike your body's stress response unless you're also under other pressures.

Men with a lot of belly fat tend to have higher stress hormone levels during the day, but their nighttime levels stay normal—like their body’s stress clock is out of sync.

People who work night shifts or irregular hours tend to have weird cortisol patterns—low in the morning and high at night—which seems to make their sleep worse. This might be because their body’s internal clock is out of sync with their work schedule.