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Nearly 40 per cent of Auckland University students in a survey had significant sleep problems, with depression and anxiety the leading causes.
Other causes were suffering from a delayed cycle of sleeping and waking, problematic alcohol use and "parasomnias" such as sleep-walking, sleep-talking and tooth-grinding.
The researchers said it was the first New Zealand study to explore rates of causes of sleep symptoms in young adults.
The survey, conducted among students at six schools at the university, also found rates of depression and anxiety that were slightly lower than those reported for the general population aged 16 to 24 in a national survey in 2003.
The study, by Auckland University and Middlemore Hospital researchers and published in today's NZ Medical Journal, found medical students had lower rates of depression than those in other fields.
Rates of potential problem drinking were higher among students of engineering, law and architecture than among medical, nursing and health science students.
One of the researchers, Auckland University psychiatrist and sleep specialist Dr Tony Fernando, said the survey showed that sleep disorders, depression, anxiety and alcohol problems started when people were young.
"We need to know how common it is so we can address it at an early stage."
Ten per cent of all respondents had delayed sleep phase disorder, in which, typically, people can't get to sleep until after midnight and in some cases much later.
Dr Fernando said the disorder was a worse form of the normal, mild tendency of teenagers and young adults to go to sleep -- and to prefer to wake up -- later than younger and older people.
High schools and universities ought to consider starting and finishing academic classes later to accommodate this.
He said the majority of patients diagnosed with the disorder experienced improvements following treatment.
"We can make it much easier for them. It's possible to adjust their body clock by two to three hours earlier."
Others went to sleep as early as 5pm and woke soon after midnight. This was quite rare and harder to treat.
The researchers say the rates of recent suicidal thoughts or self-harm in the survey were similar to rates found in studies of tertiary students overseas.
Potential causes for depression and anxiety among such people include long work hours, sleep deprivation, increasing debt, challenging career decisions and uncertainty about job prospects.
1292 Auckland University students completed the questionnaire
39% - had significant sleeping problems for more than a month
17% - depression
20% - anxiety
16% - potential drinking problem
9% - used recreational drugs in the preceding three months
7% - recent thoughts of being "better off dead" or of hurting themselves
62% - "satisfied" or "extremely satisfied" with life
Source: NZ Medical Journal