A West Australian study of more than 500 people who suffered from obstructive sleep apnoea, but were yet to begin treatment, has found more than 40 per cent of them also experienced problems with their memory.
These sufferers also reported higher rates of depression, anxiety and stress.
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Dr Romola Bucks, from the University of WA, said this pointed to the way poor quality sleep could have a major, but often overlooked, impact on mental health.
It could be the "silent disorder" behind a host of depressive illness and cognitive problems across the community, she said.