Want to stay mentally healthy in old age? Stimulating your brain by going to university or taking on leadership roles at work may help, a new study suggests.

The research led by University of Exeter in the UK used data from more than 2,000 mentally fit people over the age of 65.

Researchers examined the theory that experiences in early or mid life which challenge the brain make people more resilient to changes resulting from age or illness – they have higher "cognitive reserve".

The analysis found that people with higher levels of reserve are more likely to stay mentally fit for longer, making the brain more resilient to illnesses such as dementia.

"Losing mental ability is not inevitable in later life.

We know that we can all take action to increase our chances of maintaining our own mental health, through healthy living and engaging in stimulating activities," Linda Clare, Professor at the University of Exeter, said.

"It is important that we understand how and why this occurs, so we can give people meaningful and effective measures to take control of living full and active lives into older age.

"People who engage in stimulating activity which stretches the brain, challenging it to use different strategies that exercise a variety of networks, have higher Cognitive reserve'," said Clare.

"This builds a buffer in the brain, making it more resilient. It means signs of decline only become evident at a higher threshold of illness or decay than when this buffer is absent," she said.

The research team analysed whether a healthy lifestyle was associated with better performance on a mental ability test.

They found that a healthy diet, more physical activity, more social and mentally stimulating activity and moderate alcohol consumption all seemed to boost cognitive performance.

"We found that people with a healthier lifestyle had better scores on tests of mental ability, and this was partly accounted for by their level of cognitive reserve," said Professor Bob Woods of Bangor University in the UK.

"Our results highlight the important of policies and measures that encourage older people to make changes in their diet, exercise more, and engage in more socially oriented and mentally stimulating activities," Woods said.

The study was published in the journal PLOS Medicine.