Yes, I get a BG spike about 5 min after getting hit by hot water (about 2 mmol/L) and CGM rises likewise. Both remain high unless prebolused. I'm assuming its the work of those stress hormones, cortisol, epinephrine and glucagon.
Do you always have a shower in the morning? Do you think the BG rise might in fact be due to
dawn-effect foot-on-the-floor (with an additional apparent rise in the CGM, potentially for other reasons re calibration, etc.)? I could imagine that getting in the shower first thing might well be the kick that starts the stress hormones going. My
dawn effect foot-on-the-floor doesn't register for about 10min after getting up (on the CGM, so it is probably actually happening as soon as I get up.)
I don't have a shower straight after getting up these days - I usual need to persuade/drag my children from their beds, chivvy them into getting ready and then drive them to school, and then am either WFH, so tend to either do some admin so I know what's coming or sit in a 9am meeting if one's scheduled. If I'm going to work I tend to ride my bike so don't bother with a shower before leaving.
As I tend to have a shower later in the day (lunchtime after an exercise loop on the bike if WFH) or at work/in the evening if doing my cycle commute, this means there's no dawn effect/foot-on-the-floor in progress so I see that my CGM rise (though I accept we're all different of course!) is transient. I suppose it's possible my actual BG is also rising then falling rapidly back to where it was by the time I'm dressed. If I remember I'll try to stick my hand out of the shower and do a blood test one day to see what it says, though like you the CGM rise is only on the order of a couple of mmol/l so how easily I'll be able to pick that out of the usual noise is hard to tell.
Edit: changed "dawn effect" to foot-on-the-floor -> not enough coffee before writing the post!
