How much does sleeping heart rate change from night to night?

In members wearing the Ultrahuman Ring, sleeping heart rate changed by 3.9 bpm between back-to-back nights on average (likely between 3.8 and 4.0 bpm). On average, 26.1% of a member's nights were high nights, at least 3 bpm above their usual level. That share was likely between 25.7% and 26.5% across 1,483 members.

How much does sleeping heart rate change between nights?

Sleeping heart rate in these members moved by a few beats per minute between back-to-back nights, up or down.

Each member's nights over four months counted when the ring recorded a valid sleeping heart rate, all on the member's most-used ring and firmware version. A member needed at least 60 such nights. A member's usual level was the middle value of their counted nights, so half their nights sat above it and half below.

The change between nights was the difference between one night and the next, whichever way it went, averaged over every pair of back-to-back nights. A high night sat at least 3 bpm above the member's usual level, and a larger rise at least 5 bpm above it.

Each member counted equally, however many nights they recorded; the uncertainty ranges resampled whole members.

The top bar in the chart above is the average change between back-to-back nights. The second bar shows how far a member's nights typically sat from their own average. That spread averaged 4.6 bpm (likely between 4.5 and 4.7 bpm). Both bars compare each member with their own nights, so the chart shows movement around each person's own level. In a study of 92,457 adults wearing a wrist tracker, resting heart rate differed widely between people but was much more consistent within each person over time [1]. For most of them it stayed fairly stable over the short term, but 20% had at least one week in which it moved by 10 bpm or more [1]. These are resting readings from a wrist tracker, a different measure from sleeping heart rate. The page on resting heart rate by age covers how resting heart rate differs by age and sex.

How often does sleeping heart rate run high?

High nights, when sleeping heart rate sat at least 3 bpm above the member's usual level, came up regularly, and larger rises were rarer.

Each bar in the chart above is the average share of a member's nights at or past one cutoff above or below their usual level. The bar for the smallest cutoff, 2 bpm above usual, therefore also counts every high night and larger rise. Nights at least 8 bpm above usual made up 7.1% of a member's nights (likely between 6.8% and 7.4%), about 2 nights a month.

How well do wearables track sleeping heart rate?

Wearables differ in how well they track heart rate during sleep, and this analysis did not check the Ultrahuman Ring against a clinical recording. In a study of healthy adults, the accuracy of resting heart rate during sleep differed between wearable devices checked against an electrocardiogram [2]. A study comparing Apple Watch with a chest strap found accurate resting heart rate readings [3]. Both studies checked resting heart rate, a related measure, and neither tested the Ultrahuman Ring.

What this analysis can't tell you

The analysis had no record of illness, alcohol, training, or stress, so it cannot say why a night ran high. Travel across time zones was not accounted for. The share of high nights depends on how the usual level was set. When each member's average night was used in place of their middle night, the share of high nights was smaller. Nights the ring missed were left out, so the counted nights may skip some of the most disrupted ones. Members who wear the ring on most nights may have steadier nights than most adults, so the group may understate how much nights move in the wider population. Part of the change between nights may also come from the measurement itself.

Frequently asked questions

Is one high night of sleeping heart rate unusual?

No: a night at least 3 bpm above usual came about 2 nights a week in this group. The analysis compared each member's nights with that member's own usual level. A rate far from your usual level that stays there may be worth a conversation with your clinician.

Is sleeping heart rate the same as resting heart rate?

No. Sleeping heart rate is your average heart rate across the whole night's sleep. Resting heart rate is a separate measure, covered in Ultrahuman's resting heart rate explainer, so the numbers here don't apply to it.

Who should not read this as being about them?

These findings may not fit people whose nights are shaped by shift work, a newborn, or illness, because the analysis had no record of those things. People with a diagnosed heart rhythm condition were not studied as a separate group. Children were not included, because the analysis covered adults.

References