The controversial theory comes from visiting Harvard psychiatry professor Robert Stickgold.

Professor Stickgold will tell the Australasian Sleep Conference in Adelaide today that sleep deprivation is not just linked to, but actually causes, major psychiatric disorders in people.

''It could very well be that the increases we're seeing in some of these disorders are a direct reflection of the increasing loss of sleep in the general population,'' he said.

''This is staggering if it's proven to be concrete and it suggests that taking a closer look at the sleeping habits of mentally ill people could be key to treating their condition.'' Professor Stickgold will present evidence to the conference backing his theory including studies of children in the United States with the disrupted breathing condition, sleep apnoea, caused by enlarged tonsils.

''These children have massively disrupted sleep and are five times more likely to have ADHD [attention deficit hyperactivity disorder] but if you treat their condition by removing their tonsils their ADHD improves dramatically,'' he said.

''That shows the condition is at least partly caused by the problematic sleep.''

He said sleep apnoea was also five times more common in people with major depression, suggesting a similar link.

''This isn't just a small corner of the depression population.

''This is a lot of people that might never have been diagnosed with depression if they were able to get a good night's sleep.''

Professor Stickgold's theory extends to bipolar disorder, where he believes lack of sleep can switch a person from the depressed to manic cycle in their illness.

He also believes lack of sleep can trigger the anxiety condition, post-traumatic stress disorder, because a person is unable to sleep and receive the necessary ''memory processing'' needed to work through the trauma.

Professor Ron Grunstein, of Sydney's Woolcock Institute of Medical Research, said there was growing evidence of the causal links between lack of sleep and mental illness.

''A closer look at the quality and quantity of sleep in these patients can only help,'' he said. AAP