What changes heart rate variability (hrv)

Beat-to-beat variation in heart rate during sleep. Higher than your own usual is generally better.

Every page below says it can change this metric. Strongest evidence first. Each page's "Effect on your sleep score" section says how much and how sure we are.

AlcoholAlcohol can help you fall asleep, then breaks up the second half of the night, cuts REM sleep, raises your heart rate and lowers HRV. Less, and earlier, is better.
- Evidence: Strong
- Medium effort
- Free
- Works: tonight
Darkness and eye masksMake the bedroom as dark as you can, with blackout curtains or an eye mask. Experts recommend under 1 lux at the eye while you sleep.
- Evidence: Some
- Low effort
- Low cost
- Works: tonight
Exercise timingRegular exercise helps sleep a little. Evening exercise is fine for most people; just finish hard sessions more than an hour before bed.
- Evidence: Some
- Medium effort
- Free
- Works: a few weeks
HRV, resting heart rate and temperatureWhat your overnight HRV, resting heart rate and skin temperature mean, what moves them, and why to compare them only with your own baseline.
- Evidence: Some
- Low effort
- Free
- Works: 1–3 weeks
Room temperatureKeep the bedroom between about 18 and 25 °C (64–77 °F), and use bedding to fine-tune. Heat harms sleep more clearly than mild cool.
- Evidence: Some
- Low effort
- Low cost
- Works: tonight
What sleep scores measureWhat goes into the sleep and readiness scores from Oura, WHOOP, Apple Watch and Garmin, according to each company's own documentation.
- Evidence: Some
- Low effort
- Free
- Works: today
Which habits change which metricA table of common sleep habits against the numbers your wearable shows, with the direction of each effect, how sure the research is, and where nobody has looked.
- Evidence: Some
- Low effort
- Free
- Works: tonight to 2 weeks
Breathing techniquesSlow breathing at about 6 breaths a minute reliably raises HRV while you do it. Evidence that it improves sleep is small but promising; 4-7-8 and box breathing have even less.
- Evidence: Weak
- Low effort
- Free
- Works: tonight
SaunaMany regular sauna users say it helps them sleep, but no good trial has tested it. If you enjoy it, finish an hour or two before bed, drink water and skip the alcohol.
- Evidence: Weak
- Medium effort
- Medium cost
- Works: tonight