You could have dementia if...

Researchers found those who had orthostatic hypotension had a 54 per cent higher risk of developing dementia.

Photograph: Kind courtesy Bhernandez/Creative Commons

People who feel faint, dizzy or lightheaded when standing up -- caused by a sudden drop in blood pressure -- may be at a greater risk of developing dementia or stroke decades later, a study has found.

The study, published in journal of the American Academy of Neurology, involved 11,709 people with an average age of 54 who were followed for an average of 25 years.

Participants met with researchers up to five times over the course of the study. None had a history of heart disease or stroke at the beginning of the study.

"Orthostatic hypotension has been linked to heart disease, fainting and falls, so we wanted to conduct a large study to determine if this form of low blood pressure was also linked to problems in the brain, specifically dementia," said Andreea Rawlings, from Johns Hopkins Bloomberg School of Public Health in the US.

For the study, low blood pressure upon standing was defined as a drop of at least 20 millimetres of mercury (mmHg) in systolic blood pressure, which is the pressure in the blood vessels when the heart beats, or at least 10 mmHg in diastolic blood pressure, the pressure when the heart is at rest.

Normal blood pressure is less than 120/80 mmHg. During the initial exam, participants were screened for orthostatic hypotension.

They were instructed to lie down for 20 minutes and then stand up in a smooth, swift motion.

Blood pressure was taken five times upon standing. Researchers determined the average of the readings and then calculated the difference from the participant's average resting blood pressure.

Researchers determined that 552 participants, or 4.7 per cent, had orthostatic hypotension at the start of the study.

They monitored participants throughout the study for dementia and stroke with study visits and by reviewing medical records.

During the study, 1,068 people developed dementia and 842 people had an ischemic stroke, which is a stroke where blood flow is blocked to part of the brain.

Researchers found those who had orthostatic hypotension at the beginning of the study had a 54 per cent higher risk of developing dementia than those who did not have orthostatic hypotension at the beginning of the study.

A total of 999 of the 11,156 without orthostatic hypotension, or nine per cent, developed dementia, compared to 69 of the 552 people with orthostatic hypotension, or 12.5 per cent.

In addition, those with orthostatic hypotension had twice the risk of ischemic stroke. A total of 15.2 per cent, or 84 of 552 people, with orthostatic hypotension had an ischemic stroke, compared to 6.8 per cent, or 758 of 11,157 people without orthostatic hypotension.

There was no association with bleeding strokes.

"Measuring orthostatic hypotension in middle-age may be a new way to identify people who need to be carefully monitored for dementia or stroke," said Rawlings.

"More studies are needed to clarify what may be causing these links as well as to investigate possible prevention strategies," she said.