High fasting blood sugar: the causes and what to do tonight.

On Tuesday your work health check results arrive. All fine except one line: high fasting blood sugar, just over the limit. Your GP says 'keep an eye on it'. And you think: I hadn't even had breakfast.

I see it often in the people I work with: they cut out bread and keep the five-hour nights. High morning blood sugar usually starts in the hours before the test, and that's where you can act.

What the number tells you

• Your liver works all night. Over half a day's insulin is used while you're fasting, to keep it in check.
• At dawn your body gets ready. Between five and eight, growth hormone and cortisol nudge blood sugar up, even in healthy people. If you compensate well, it won't show on the test.
• One result is a snapshot of one morning. High only on waking and normal the rest of the day, it may owe more to cortisol than to insulin working poorly. Your doctor will judge that.

Why is my blood sugar high in the morning if I haven't eaten?

Because when you're fasting your liver makes the sugar, and overnight it can make more than you need. Short sleep, stress and idle muscles push it that way.

The short night. For blood sugar, deep sleep matters most. A single five-hour night can make insulin work less well the next morning, and your liver releases more sugar.

Stress that stays switched on. Cortisol should rise when you wake and fall in the evening. If it stays high all day, your blood sugar tends to follow.

Your belly and your liver. Fat around the middle sends its fatty acids straight to the liver, which then listens less to insulin and puts less of a brake on the sugar it makes overnight.

Muscles at rest. Muscle is the main store for sugar, and trained muscle takes up more. But the advantage doesn't last: two or three days without moving and it's gone.

High fasting blood sugar: what to do tonight

Eat early and light, with your carbs at lunch. Finish three hours before bed. At night your sleep hormone holds insulin back, so a late snack catches your body off guard. On the plate: vegetables with fish, eggs or pulses. Move the bread, pasta and rice to lunch, when insulin works better. If your morning sugar is normal, a portion at dinner is fine. A common mistake is skipping dinner to bring the number down. Under stress, fasting calls up cortisol, and your morning sugar can rise anyway.

Walk for ten to fifteen minutes after dinner. Working muscles clear some of dinner's sugar before bed.

Never two days in a row without moving. Two strength sessions a week build the store. On other days walk, take the stairs or cycle, because what you gain fades quickly.

Seven or eight hours, protected. That's the range where the risk linked to blood sugar is lowest. Keep the bedroom dark and quiet, and screens down after dinner: noise and light break up deep sleep.

Start with tonight's dinner. At your next test, tell your doctor how these weeks have gone too.