Most people think heart rate variability (HRV) is just something you check after a big workout, a long run or a brutal gym session. 

But here’s the twist, your HRV at night might be one of the most insightful indicators of how your body is coping with life’s stressors during the day. And if you’ve ever wondered why companies track it, it’s because it reveals information your sleep score never could.

So, what actually is HRV?

Think of your heartbeat like footsteps. Some steps are slightly closer together, some slightly further apart, even when you’re just walking in a straight line.

HRV measures those tiny variations between each beat. Not in a creepy, medical way, but in a “how flexible is your nervous system right now?” way.

  • Higher HRV correlates with rest, exercise and good recovery1
  • Lower HRV  is an effect of stress, illness and inflammation1 

At night, HRV becomes even more interesting. It’s one of the only times your body isn’t trying to answer emails, digest dinner or panic-scroll TikTok. It’s just… being.

That makes your overnight HRV a kind of internal whisper that reveals how you’re really doing.

‍HRV is personal

If your friend has an HRV of 110 and yours is 45, it doesn’t mean anything is wrong. HRV is influenced by many things including age, sex, genetics, fitness level, hormones, food, hydration, alcohol, menstrual cycle, anxiety, travel, illness, inflammation… the list genuinely goes on.1,2 

That’s why comparing your HRV to anyone else’s is like comparing fingerprints. The number itself isn’t the point. The trend is. One low night? Normal. A week of lower-than-your-usual nights? That’s when your body is nudging you for attention.

Why sleep and HRV are locked in a two-way conversation

People love asking: “Does poor sleep make HRV worse… or does low HRV cause poor sleep?” The answer is yes. Both. 

When sleep is poor your HRV dips and your stress hormones stay elevated; you drift in and out of sleep cycles and your heart works harder to keep things balanced. 

When HRV is low, sleep becomes more difficult. Your system is already on high alert, it takes longer to fall asleep, you wake more frequently, and you spend less time in deep, restorative phases of sleep. It becomes a loop – not a doom loop, just a very human one.3 

‍What actually improves HRV (and your sleep) the most?5-8

Not hacks. Not supplements. Not optimised protocols.

  • Good sleep quality8
  • Less alcohol7
  • Breathing slowly before bed6
  • Moving your body during the day5
  • Letting your nervous system exhale6

So, should you pay attention to HRV at night? 

Yes but gently. HRV is one of those “holy grail” metrics people can get a little too attached to. 

Like REM sleep, it’s easy to start worrying about the number instead of paying attention to what it’s trying to show you. HRV naturally rises and falls and it’s not a report card on your progress, just one signal in a much bigger conversation your body is having. 

If it sits lower than your usual range for a few days, that’s your cue to return to the basics.

References: 

  1. Olivieri F, Biscetti L, Pimpini L, Pelliccioni G, Sabbatinelli J, Giunta S. Heart rate variability and autonomic nervous system imbalance: Potential biomarkers and detectable hallmarks of aging and inflammaging. Ageing Res Rev. 2024;101:102521.
  2. Sammito S, Thielmann B, Böckelmann I. Update: factors influencing heart rate variability-a narrative review. Front Physiol. 2024; 6;15:1430458.
  3. da Estrela C, McGrath J, Booij L, Gouin JP. Heart Rate Variability, Sleep Quality, and Depression in the Context of Chronic Stress. Ann Behav Med. 2021; 16;55(2):155-164.
  4. Routledge FS, Campbell TS, McFetridge-Durdle JA, Bacon SL. Improvements in heart rate variability with exercise therapy. Can J Cardiol. 2010; 26(6):303-12.
  5. Steffen PR, Bartlett D, Channell RM, Jackman K, Cressman M, Bills J, Pescatello M. Integrating Breathing Techniques Into Psychotherapy to Improve HRV: Which Approach Is Best? Front Psychol. 2021; 15;12:624254.
  6. Timothy A, Sharma S, Sharma S. Changes in heart rate variability in patients of alcohol dependence syndrome-Do we have a biomarker for craving? Indian J Psychiatry. 2025; 67(10):969-975.
  7. Sajjadieh A, Shahsavari A, Safaei A, Penzel T, Schoebel C, Fietze I, Mozafarian N, Amra B, Kelishadi R. The Association of Sleep Duration and Quality with Heart Rate Variability and Blood Pressure. Tanaffos. 2020; 19(2):135-143.