Can't concentrate at work: win back one hour of full attention.

'I can't concentrate at work.' I hear it often, and the scene is nearly always the same. Half past ten, a contract to review. You read the same line three times, answer a message, open your inbox. By midday you have ten things open and none finished.

Most people blame their age. I look at how you slept, how much water you've had, what was on your plate and where your phone is. Anyone who asks me for a trick to focus nearly always has a gap in one of those.

Wandering attention: the signs

• You reread. The same line three times, and it still hasn't gone in.
• You interrupt yourself. Nobody was after you. You open your inbox mid-sentence.
• Some days it's everything. 'I can't focus on anything', even a film. Usually after a short night.

Why can't I concentrate at work?

Usually for two reasons at once. You reach your desk with your body running low, and the day interrupts you before your attention has warmed up.

Every interruption has a price. A call lasts a minute, but getting back to where you were takes several. If that happens a few times an hour, you rarely reach deep work at all.

Many are your own. Staying with a hard task is tiring, and distraction brings relief. Your inbox gives your brain a small, instant reward, so you open it at the hardest paragraph.

A short night shows up at ten. While you sleep, your brain prunes the day's connections and keeps the ones that matter. After a short night your attention dips.

Too little water, and digestion. Lose about one per cent of your body's water without replacing it that day, and your head underperforms. After lunch, digestion asks you to slow down. That's a good time for meetings, calls and email.

How to improve concentration, starting with your body

One hour a day, between nine and twelve. That's when your mind usually sharpens, peaking around midday. Put it in your diary like a meeting, with one task only. A full block runs sixty to ninety minutes; if that feels long, start with twenty-five or thirty and build up. Then a few minutes on your feet, away from your phone.

Phone in a drawer. Or in your bag, on silent. Face down on the desk is a start, but it's still within reach. With a drawer in the way, you think twice before picking it up. Inbox closed. Keep paper by the keyboard: when a thought turns up, write it down and go back to the task.

Move before the block. After a training session, attention and reaction times stay sharper for at least two hours. If you train in the morning, put the work that matters straight afterwards.

Light, water, coffee. Ten minutes of outdoor light within an hour of waking, because daylight helps keep you alert. A glass of water before you start. Coffee peaks after about forty minutes and helps your attention last, so have it before the block. Last one straight after lunch.

At lunch, vegetables and protein before carbs. Your blood sugar rises more slowly, and your head usually holds up better mid-afternoon.

Start tomorrow with a single block. Keep it up for two weeks and see how much work you finish before lunch.