By Agence France Presse "This is a public health issue that can no longer be ignored," said study co-author Malcolm van Schantz of the University of Surrey -- and argued that "night types" should be allowed to start and finish work later in the day. "Night owls trying to live in a morning-lark world may (suffer) health consequences," said fellow author Kristen Knutson of the Northwestern University in Chicago. The duo gathered information on nearly half-a-million people aged 38-73 from a public database. The participants had defined themselves as either "definitely a morning person" (27 percent), "more a morning person than evening person" (35 percent), "more an evening than a morning person" (28 percent), or "definitely an evening person" (nine percent). They also listed their weight, smoking habits, and socioeconomic status. Deaths in the group -- just over 10,500 in total -- were documented for six-and-a-half years. The night owl group, the team found, had a 10-percent higher risk of dying than those in the extreme early-morning group. People in the late-night group were more likely to suffer from psychological disorders, diabetes, and stomach and breathing troubles, and slept fewer hours per night. They were also more likely to smoke, drink alcohol and coffee, and use illegal drugs. The higher risk may be because "people who are up late have an internal biological clock that doesn't match their external environment," Knutson said. "It could be psychological stress, eating at the wrong time for the body, not exercising enough, not sleeping enough, being awake at night by yourself, maybe drug or alcohol use." The research duo urged special treatment for night owls. "If you can recognise these (types) are, in part, genetically determined and not just a character flaw, jobs and work hours could have more flexibility for owls," Knutson said. "They shouldn't be forced to get up for an 8.00 am shift."