Interesting article about how the Apple Watch can detect diabetes with 85% accuracy:
https://app.upbeatpr.com/stories/cardiogram/cardiogram-android-4-2/
This goes along with what I believe about insulin affecting heart rate. When insulin is high–especially with insulin resistance–heart rate is high. In the mornings my heart rate is often 80+. However, by the evening, it is usually 50.