Doing crosswords, using a computer, keeping a journal and playing games such as chess may help older people ward off dementia.

A Monash University study suggested Australians over 70 who regularly did those activities were nine to eleven per cent less likely to develop the condition.

That compares with a seven per cent reduction in dementia risk for people who do activities the researchers said were more passive like painting, knitting and crafting.

The findings were based on data from more than 10,300 Australians involved in the ASPREE longitudinal study of older adults and the findings were published in the journal JAMA Network Open.

Frequent outings to places like restaurants or cinemas and the size of a person's social network were not shown to have an impact on reducing dementia risk.

The findings were consistent across education level, gender and socioeconomic status.

Senior author Associate Professor Joanne Ryan said it was critical to identify strategies that could prevent or delay dementia.

"What our results tell us is that active manipulation of previously stored knowledge may play a greater role in dementia risk reduction than more passive recreational activities," Associate Professor Ryan said.

"Keeping the mind active and challenged may be particularly important."

However, she noted there were some limitations in the research such as whether results in people naturally drawn to activities associated with cognitive health were influenced by other lifestyle behaviours.

Those taking part in the study were also more likely to be living healthier lives than the general population.

"While engaging in literacy and mental acuity activities may not be a magic pill to avoid dementia, if that was your goal and you had to choose, our research certainly suggests these are the activities most likely to support prolonged good cognitive health," she added.