kyriakosel

Founder here

We worked on a publication for NPJ biological timing and sleep

A few things that are surprising from the research

- sleep duration decreases by 4.4 minutes for each additional hour of daylight

- The effect didnt get much stronger at higher altitudes (even though daylight swings are much larger)

Plain English summary here

https://tryterra.co/research/terra-research-nature-publicati...

great

that would be interesting to study - let me follow up on this

anecdotal -but- it took me 6 months after covid for my breathing rate to go back to normal, and to be able to do consistent max our efforts of >190BPM for >5 seconds like previously

indeed - fixed now, let me know if you can see it!

Cyprus summers are like 45C and its almost like a sauna :)

i was mostly refering to humidity/duration/temperature given that most devices do not report back these values

it works for me - what browser are you using?

Fair flag: 256 users, 59k days

we agree - but thats not that simple :)

Agreed - one is muscular/metabolic demand, the other (sauna) is thermoregulation.

Agreed on the long-term effect too: doing a study on long term health is a completely different story

Author here. Methodology upfront because I'd ask the same things:

Data: daily records from wearable users who logged sauna sessions via connected apps. Within-person design — each user is their own control, comparing their own sauna-day nights against their own non-sauna-day nights. No cross-user comparisons.

Stats: paired t-tests, FDR-corrected p < 0.05, Cohen's d > 0.2 threshold for "meaningful effect." Anything below d=0.2 we don't report as a finding.

What we measured: minimum nighttime HR, max and average HR, HRV, activity minutes and distance, menstrual cycle phase (for female subset).

What we found: - On sauna days, minimum nighttime HR drops ~3 bpm (~5%) vs. the same user's non-sauna days. - Effect survives controlling for activity level. It's not "sauna users just exercised more that day." - Strongest hypothesis: elevated parasympathetic tone from the post-sauna cooling phase carries into sleep. Consistent with heat-stress physiology literature. - Sex difference: for women, the nighttime HR effect only crosses the d > 0.2 threshold during the luteal phase. No meaningful effect during the follicular phase. We didn't expect this; worth replicating.

What we can't control for: - Sauna type (dry / infrared / steam), duration, temperature. Not captured. - Dose-response. We don't know session length per user. - Timing of sauna relative to sleep. - Reverse causation: people may sauna on days they already feel recovered. - Selection: wearable users who bother logging sauna are a health-conscious cohort.

What surprised us: the effect is larger than what we see for comparable-intensity exercise days. If you treat nighttime HR as a parasympathetic recovery signal, sauna beats a moderate workout on the same user. Not what I'd have predicted.

certainly - their ecosystem is a big reason why they are here

There are too many books that I would want to listen to and don't have audiobooks. i'd definitely give it a try with that in mind

TERRA (YC W21) | LONDON | Full-Time/On-Site |

Terra is an API for apps to connect to wearables and sensors. We are Backed by YC, General Catalyst, and many more

Positions: | AI Engineer | Software Engineer | Growth Engineer | Product Engineer

I'm shocked by how realistic it sounds. Can we embed it in our website/blog ?