The cry of frazzled workers everywhere has always been "I'm dying for a coffee".
But if you're feeling tired then you should be pouring yourself an orange juice instead, say scientists.
Researchers have found the drink helps to boost alertness, concentration and reaction times.
What is more, the effects last for hours, with those who have juice at breakfast more alert than others by mid-afternoon.
Reading University researchers put 24 men through a battery of mental tests over two days.
On one of the days, they had a glass of orange juice before the tasks and on the other a flavoured, sugary water that looked and tasted like orange juice.
After the real juice they did better on tests of speed and attention and still felt very alert six hours later, the European Journal of Nutrition reports. Just 240ml - or a small carton - was enough to give the brain a boost, the study found.
