Dizzy spells experienced in middle age when standing up have been linked to an increased risk of dementia.
The brief drop in blood pressure that causes the dizziness may result in lasting damage to the brain, scientists believe.
A study found that the effect, known as orthostatic hypotension, upped the chances of developing dementia in old age by 40pc.
Lead researcher Dr Andreea Rawlings, from the Johns Hopkins Bloomberg School of Public Health in the US, said: "Even though these episodes are fleeting, they may have impacts that are long lasting.
"We found that those people who suffered from orthostatic hypotension in middle age were 40pc more likely to develop dementia than those who did not. It's a significant finding and we need to better understand just what is happening."