Poor sleep in old age can result in brain changes associated with dementia, scientists have found.
Study participants who spent the least amount of time in deep "slow wave" sleep were significantly more likely to lose brain cells than those who slept the most deeply.
The research also showed that lack of oxygen caused by the snoring condition sleep apnoea increased the risk of tiny areas of damage in the brain nearly four times.
Sleep apnoea occurs when the airway becomes repeatedly blocked, leading sufferers to snore and often wake up as they struggle for breath.
The study involved 167 men from Hawaii with an average age of 84 who had sleep tests conducted at their homes.
After they died an average of six years later, post mortems were conducted on their brains to look for changes such as loss of neurons and "microinfarcts" - areas of dead tissue caused by oxygen starvation.
Of the 37 men who spent the least time in slow wave sleep, 17 had brain cell loss compared with seven of the 38 who spent the most time in slow wave sleep.
Dr Rebecca Gelber, from the Pacific Health Research and Education Institute in Honolulu, Hawaii, said: "These findings suggest that low blood oxygen levels and reduced slow wave sleep may contribute to the processes that lead to cognitive decline and dementia."