A study has found couch potatoes are at much higher risk of mental health issues, heart disease and diabetes.

The Baker Heart and Diabetes Institute research found mentally-passive, sedentary behaviour increased the risk of depression.

But mentally-active, yet sedentary behaviour like reading or office work may protect against the onset of depression.

Professor David Dunstan says reducing Australians passive, sedentary behaviour - like watching TV - may help reduce the risk of future depression.

"In the context of psychological wellbeing, the way we use our brain while sitting appears to be important," Professor Dunstan said on Tuesday.

The average Australian adult sits for approximately nine hours per day.

Physical and mental health risks of too much sitting can be offset by exercise.

Researchers said more research was needed to clearly establish the links between sedentary behaviour and depression.

The study paper also called for more research to determine what types of sedentary behaviour would increase depression risk, as well as what factor genetics may have.

Melbourne resident Joanna Thorne, 34, who was diagnosed with depression when she was a teenager, was told to take up reading.

She said her mind tended to worry the most before she went to sleep but reading helped her focus.

"The saying goes 'use it or lose it' so I read regularly to keep my mind active and my imagination stimulated," Ms Thorne said.

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Australian Associated Press