People who take about 30 minutes of nap during daytime may have improved brain health that can significantly lower the risk of dementia, according to a study.

The study led by researchers at University College London in the UK and the University of the Republic in Uruguay showed that daytime napping slowed the rate at which brains shrink as we age, by seven years.

The study, published in the journal Sleep Health, gathered data from almost 400,000 people in Britain aged between 40 and 69.

The findings showed that the average difference in brain volume or the size of the organ between people programmed to be habitual nappers and those who were not was equivalent to 2.6 to 6.5 years of ageing.

"Our findings suggest that, for some people, short daytime naps may be a part of the puzzle that could help preserve the health of the brain as we get older," said Dr Victoria Garfield, MRC Unit for Lifelong Health & Ageing at UCL.

In the study, the researchers looked at 97 snippets of DNA thought to determine people's likelihood of habitual napping. MRI scans revealed that their brain volume was 15.8 cubic centimetres bigger than those who did not nap.

They, however, found no link between napping and the size of the hippocampus -- the region of the brain linked to memory and learning.

"This is the first study to attempt to untangle the causal relationship between habitual daytime napping and cognitive and structural brain outcomes. Our study points to a causal link between habitual napping and larger total brain volume," said lead author Valentina Paz, from the University of the Republic and UCL.

"I hope studies such as this one showing the health benefits of short naps can help to reduce any stigma that still exists around daytime napping," added Dr Garfield.