Having a stroke or snoring can increase the risk of developing Alzheimer's disease, new research has shown.
Both result in a lack of oxygen reaching the brain which can have a negative effect on brain cells.
The lack of oxygen blocks the expression of proteins needed for brain cells to carry out their functions, causing the cells to become toxic.
Professor Chris Peers, who contributed to the study, said: "We are looking into what happens when oxygen levels in the brain are reduced by a number of factors, from long-term conditions like emphysema and angina, to sudden incidents such as a heart attack, stroke or even head trauma."
Of such factors he said: "Even though the patient may outwardly recover, the hidden cell damage may be irreversible.
"It could even be an issue for people who snore heavily, whose sleep patterns are such that there will be times in the night when their brain is hypoxic: deprived of sufficient oxygen."
The research has been welcomed by the Alzheimer's Society.