Taking heartburn medication for longer than four-and-a-half years could raise the risk of developing dementia in later life.
A study looked at drugs called proton pump inhibitors, or PPIs, which are taken for acid reflux and heartburn by more than 15million people in the US and UK each year.
Researchers analyzed 5,712 people, aged 45 to 64 when they were recruited to a health study in the late 1980s.
The volunteers were regularly asked what medications they were taking up until 2011, when they were aged 75 on average, to calculate the length of time they used PPIs.