Heart Rate indication of T2D

[harbottle]

In 2021, before diagnosis, I went for 50+ checkup. My resting heart rate was 100 so they gave me an ECG. Then a blood test…


I have been looking at the historical data on my watch recorded and noticed that in May that year, my resting heart rate (which was ahead a bit high) starting going up. This was the time my eyesight went blurry.

A bit of research online has indicated that ‘prediabetes’ can cause a slightly elevated resting heart rate (pre-May?)

So I’m wondering if this rise may be the point my BG went out of control. I was not sleeping much and very stressed early in that year.

It started to fall in October, when I went low carb (and lost weight)

 

[harbottle]

I showed this to a GP friend and he commented the same, that it looks like that's the point where the blood sugar ramped up.

 

[silver minion]

That is very interesting. My husband's cardiologist told him several years ago that illness or infection puts stress on his heart and lungs causing his BP and heart rate to rise and often triggers his AF.
I had a well woman check when I moved here but before diabetes diagnosis. I did mention my weight loss but as my BP was in normal range and resting heart rate was around 72 no further action taken. I am a non smoker and not overweight plus fairly active so I ticked all the boxes. No HbA1c check done.
My resting heart rate is now between 59 and 64 bpm, and BP is low end of normal. This is where I was for very many years. I put my higher(for me) readings down to age and life stress. My previous health check was a few years before covid. There were no red flags, then either.

 

[PerSpinasAdAstra]

I have noticed correlations between resting heart rate, blood pressure and fasting blood glucose levels. After a stressful couple of days, followed by a couple of poor nights' sleep as a result, my RHR, BP and fasting levels will all be higher in the morning after waking up. The peak of the spike after breakfast will also be higher as a result, as the spike starts at a higher 'baseline', if that makes sense. A few nights good sleep and it seems to drop back to normal.

I would guess that the single factor which influences all of these is the stress hormone cortisol. The Garmin fitness tracker I use has a stress indicator, which is based on heart rate variability. After a good nights sleep I wake up to zero 'stress' according to Garmin and a low RHR. A restless night though seems to often result in a high 'stress' reading even though I'm not actually stressed, I'm still half asleep. As far as I know cortisol is capable of influencing all of these metrics. Perhaps if the stress you experienced resulted in high fasting levels that would lead to very high spikes after eating and lead to the blurry vision?

 

[harbottle]

Here is what AI says:

Yes, that graph very likely reflects the physiological shift from prediabetes into type 2 diabetes—or at least a worsening of insulin resistance and autonomic imbalance—before your formal diagnosis.

Here’s why:

• Your resting heart rate climbs gradually from around May to October, peaking around August–October at close to 90 bpm.
• This kind of steady RHR rise is not typical unless something is stressing the system, such as:
• Worsening blood sugar control
• Increasing insulin resistance
• Systemic inflammation
• Stress or poor sleep (also common in undiagnosed diabetes)
• You were then diagnosed in October, right at the peak RHR.
• After that, there’s a steep and sustained drop, likely tied to changes you made post-diagnosis—such as diet, weight loss, and better glucose control.

⸻
What this graph may be showing:

• Mid-2021: Prediabetes progressing—RHR rising gradually.
• Late 2021: Blood sugar likely hitting diabetic levels—autonomic nervous system becomes more imbalanced.
• Post-diagnosis (Oct onward): You take action, leading to improved metabolic health and remarkably lower RHR—down to around 60 bpm by early 2022.

⸻

Why this matters:

A falling resting heart rate like yours is a powerful sign of recovery—not just from diabetes, but in overall cardiovascular and autonomic health. It reflects lower sympathetic nervous system activity, better insulin sensitivity, and lower inflammation.

Want help linking these improvements to what changes you made, or curious how this ties in with your current risk profile?

 

[harbottle]

As far as I know cortisol is capable of influencing all of these metrics. Perhaps if the stress you experienced resulted in high fasting levels that would lead to very high spikes after eating and lead to the blurry vision?

The weird thing is, my fasting levels were around 6 shortly after I was diagnosed (hba1c of 83) and before I started the low-carb diet.

I am starting to get the impression that this implies that liver insulin resistance was not present (My liver tests have all been excellent.) but the hba1c was due to post-prandial spikes. Going back further with the data I can see that my resting heart rate went up initially in 2018/19, which was also a stressful year (Redundancy plus my Mum getting cancer and dying.)

I was so stressed in 2021 that from March to October don't think I had a single night's sleep!

 

[Homer]

Very interesting on blood pressure, heart rates, I’ve had AF for over 15 years before I was diagnosed with type 1.
My heart rate according to my Apple Watch drops down when I’m sleeping to 30 beats - 35 , which happens a lot, now I should be a very fit athlete, I’m not. The advice from my GP was to throw my watch in the bin. My sugar levels are mostly the same when this happens, so to be honest I’m more concerned about being a diabetic than having heart disease.

 

[harbottle]

Why did he tell you to throw it away?
It's very accurate for resting heart rate - a little less when walking, and not so great when doing exercise. Movement and heat can affect its readings.

 

[PerSpinasAdAstra]

The weird thing is, my fasting levels were around 6 shortly after I was diagnosed (hba1c of 83) and before I started the low-carb diet.

I am starting to get the impression that this implies that liver insulin resistance was not present (My liver tests have all been excellent.) but the hba1c was due to post-prandial spikes. Going back further with the data I can see that my resting heart rate went up initially in 2018/19, which was also a stressful year (Redundancy plus my Mum getting cancer and dying.)

I was so stressed in 2021 that from March to October don't think I had a single night's sleep!

I've looked into how the fasting level 'system' works quite a bit and my current understanding is that a fasting level of 6 mmol/L might well indicate at least some insulin resistance in the liver. The fasting level is primarily governed by glucagon (from the alpha cells in the pancreas) and insulin (from the beta cells). Below around 3.9 mmol/L glucagon secretion increases greatly, and above around 4.4 mmol/L insulin secretion increases greatly. In a perfectly healthy person in normal circumstances the fasting level stays mostly within this range. Glucagon boosts glucose output from the liver and insulin reduces it. It's not a kind of on-switch and off-switch situation though - in the range between 3.9 and 4.4 there is glucagon and insulin in the blood at the time, both being secreted to some degree.

At 6 mmol/L there should be next to no glucagon being secreted and there should be loads of insulin. Glucose output from the liver should be very low. Things are complicated though by counter-regulatory hormones - cortisol, adrenaline and a load of others. A 'normal' fasting level is 5.5 mmol/L or lower - 6 is in the prediabetic range - and as far as I can tell it's liver fat that is the probable culprit. The main effect of weight loss is reducing liver fat and triglycerides.

I don't understand how inflammation fits into it all - whether inflammation causes stress on the body which causes cortisol or some other counter-regulatory hormone to be released. I primarily looked at the things that affect the liver and pancreas and that affect the action of insulin. I'll never understand it - it's all fiendishly complicated. What I can say though is that at peak after diagnosis I lost 33Kg and my fasting level (according to Contour Next) dropped to 3.8 to 4.6 mmol/L or so. I've since put nearly 10Kg back on and my (morning) fasting level is now up to 5.2 to 5.5 mmol/L. I believe this means I've built up fat in my liver again though am uncertain. I had blood tests yesterday to gather my HbA1c and triglyceride data and I'm about to lose most of the weight again. I'm hoping to gather a pile of data on how my fasting level and response after meals change after losing weight. What I'm hoping to do it test Taylor's Personal Fat Threshold to some extent. It seems like I've come close to it, or the complex reality that theory represents, and I'm going to try to gather data on the (hopefully) fall back down to my lowest possible fasting level.

Incidentally my post-prandial spikes also went up some time after my my triglycerides did (I bought a finger-stick triglyceride meter like the data junkie that I am). I can't tell if that's because of the higher fasting level though, the higher baseline, or because I'm starting to see harm to my alpha cells again due to fat building up in the pancreas. Impossible to tell, though at the very least I hope to have some interesting graphs in a couple of months (if I can get back on my diet and get it done).

Sorry to hear about your Mum. My condolences.

 

[Homer]

I think the GP was saying it can’t judge heart rates properly when you have AF, it’s ok for other things , I did ask a cardiologist about the watch , he was saying when the heart rate does go very low as it happens to me, he would ignore it unless I have pains in the chest or arms, or was sweating and I must admit this is be going on for years with the low heart rate. The GP also said how many patients have came into the surgery saying exactly what I told her and a lot of them where panicking to her opinion unless you have symptoms of having a heart attack.

 

[harbottle]

6 was a level after I'd been up and active for a while.
Even now, once I get up I see a little nudge into the 6s sometimes, which is nothing to be concerned about - the circadian rhythm means insulin sensitivity, amount secreted by the pancreas and the level beta cells release insulin at changes during the day, plus hormones like cortisol being at the peak in the morning (And dwindling during the day) - plus under 7, the secretion pretty much goes down towards 'basal' levels (Apparently) hence why you see a quick drop and then a slower curve. All designed to stop BG dropping to fast.

 

[everydayupsanddowns]

Really interesting observations @harbottle

 

[silver minion]

I think the GP was saying it can’t judge heart rates properly when you have AF, it’s ok for other things , I did ask a cardiologist about the watch , he was saying when the heart rate does go very low as it happens to me, he would ignore it unless I have pains in the chest or arms, or was sweating and I must admit this is be going on for years with the low heart rate. The GP also said how many patients have came into the surgery saying exactly what I told her and a lot of them where panicking to her opinion unless you have symptoms of having a heart attack.

My BiL was left with persistent AF following a heart attack a few years ago. As his heart beat is always irregular now he had to stop wearing his smart watch because an alarm kept going off. Fortunately he doesn't have massive rate swings and his medication mitigates the worst of the symptoms. He is also T2 diabetic. He has changed his diet and takes metformin to manage his BG and keeps as active as possible.