Coffee in smaller doses keeps us awake longer

A grande latte or double espresso in the morning is no substitute for regular small doses of caffeine throughout the day to keep you awake, researchers have found.

A grande latte or double espresso in the morning is no substitute for regular small doses of caffeine throughout the day to keep you awake, researchers have found.

Small, frequent doses of caffeine, which build up to counteract the body's natural desire for sleep, were best for truck drivers, doctors and others who needed to stay awake over a long period, according to the Sleep Disorder Centre at Rush University Medical Centre in Chicago.

"Most of the population is using caffeine the wrong way by drinking a few mugs of coffee or tea in the morning," said the centre's laboratory director, James Wyatt.

Researchers at Rush, along with others at Harvard Medical School, studied men in private suites, who had no way of knowing the time, for 29 days.

The men were scheduled to stay awake for nearly 29 hours straight, simulating the amount of time some doctors, military and emergency services personnel have to remain alert.

Those who were given a caffeine pill equivalent to two ounces of coffee every hour did better on tests than those who received a placebo, the study said. The subjects who took the caffeine pill also felt sleepier than the others when bedtime finally arrived, the study said.