Inadequate sleep increases the risk of stomach pain and ulcers, a University of Hong Kong research team has found. The study by the department of pharmacology divided 24 mice into two groups for different sleep hours and examined the function of their stomachs after a week. One group slept without interruption for an average nine hours a day, while the others were put into a rotating drum which allowed them to sleep only one hour a day. Researcher Dr Marcel Koo Wing-leung said mice that had inadequate sleep recorded a higher incidence of ulcers. After all the mice were put under cold stress for two hours, mice which had inadequate sleep had ulcers of an average 13mm in length, compared with only 4mm-long scars in the other group. Dr Koo said the sleep-deprived mice also had thinner and weaker stomach protective linings and stomach walls, making them more prone to ulcers. He said the genes that could cause gastric cancer were also found in sleep-deprived mice. 'There are many people who constantly do not have adequate sleep, like health-care workers and drivers on shifts - the studies show they will have a higher risk of ulcers,' Dr Koo said.