What is the connection between sleep and blood sugar?

Stronger than most people realise and bidirectional. Short or poor-quality sleep measurably reduces insulin sensitivity — experimental studies show meaningful reductions after only a few nights of restriction in healthy people. It also raises appetite-driving hormones and shifts food preference towards high-carbohydrate options. In the other direction, high or fluctuating blood sugar disturbs sleep, and undiagnosed obstructive sleep apnoea is both common in people with type 2 diabetes and independently worsens control. If someone has stubborn glucose readings despite good diet and medication, sleep is a genuinely worthwhile thing to examine.