Sex, simple sports and doing the crossword seem to be a good means to fend off dementia that usually comes along with ageing, according to a research.

Sex, cryptic crosswords and a good run could help ward off this and other degenerative conditions by stimulating new brain cells.

According to Perry Bartlett, a professor at the University of Queensland's Brain Institute, mental and physical exercise helped create and nurture new nerve cells in the brain, keeping it functional and warding off diseases such as Alzheimer's and Parkinson's.

He said a chemical called prolactin appeared to promote new cells in the brain and could be found in high levels in pregnant women.

"Perhaps doing something a little more inquisitive or intellectual might be good at selecting their survival so perhaps we should run a long distance and do the cryptic crossword or something like that," he said.

"If we understand these mechanisms we should be able to use them to treat neurodegenerative diseases, or even mental illnesses in the long-term," he added.