How Sleep Affects Your Blood Sugar

Sleep affects your blood sugar directly, which is why a run of bad nights can show up in your readings even when nothing about your food or medicines has changed.

A systematic review of the evidence found a significant association between insufficient sleep and insulin resistance — the state in which your body's own insulin works less well. Seven hours a night is the usual minimum for an adult; short sleep is generally counted as under six. Strikingly, a single night of partial sleep deprivation was enough to measurably increase insulin resistance compared with a full night.

Experimental work on circadian timing found much the same. When sleep was restricted to 6.5 hours, fasting glucose rose about 8% and post-meal glucose about 14%.

There is a loop here worth naming. Poor sleep raises glucose. High glucose at night means more trips to the bathroom, which breaks sleep. Stress does both. It is common to be caught in all three at once and to conclude that your diet has failed, when the problem is upstream of the plate.

What actually helps

• A consistent bedtime, more than a long one.
• Deal with a late-night high rather than assuming the broken sleep is unrelated.
• Take snoring seriously. Sleep apnoea travels closely with diabetes and is often undiagnosed — more on that here.
• Do not judge a week's readings after a bad week's sleep. The numbers are telling you about your nights.