TOKYO -- Men who sleep fewer than five hours a night run greater risks of becoming obese and of having high levels of blood sugar that could lead to diabetes, a Japanese study showed.

Lack of sleep triggers a hormone in the blood which stimulates the appetite, said the study's lead author, Nihon University medical department associate professor Yoshitaka Kaneita.

"It increases a sense of hunger as well as an appetite for high-calorie food," he said Thursday, calling for people to pay due attention to how much they sleep.

His study, released Wednesday, looked at 21,693 men in 1999 and followed up to see how they were doing in 2006.

Men who were not fat in 1999 were 1.36 times more likely to become obese if they slept fewer than five hours a night on average over the next seven years compared with men who slept more.

Short-sleepers were also 1.27 times more likely to have high blood-sugar levels.

Comparable data for women was not available.