Blood pressure drop on standing 'may be linked to dementia'Posted by Gareth Hargreaves
Following claims that blood pressure drop on standing 'may be linked to dementia', Behind the Headlines, the NHS Choices news analysis service, examines the science behind the story.
"Have you ever felt dizzy when you stand up?" asks the Mail Online. "You could be more at risk of dementia," the website warns.
Researchers in Holland found a weak link between blood pressure drops on standing and the chances of getting dementia. But whether or not people felt dizzy made no difference to the results.
Our blood circulation is designed to compensate for changes in posture to keep a constant flow of blood throughout the body, no matter what we're doing.
When we stand up, our heart automatically pumps faster to keep blood pressure up and ensure blood reaches the brain.
As we get older, that system seems to work less well, so people get short periods of lower blood pressure when they stand up, called postural, or orthostatic, hypotension (PH).
PH can cause short periods of dizziness, although many people don't notice any symptoms.
The study followed 6,204 people in their 60s or 70s for an average of 15 years. It found those who had PH at the start of the study were 15% more likely to get dementia during follow-up.
But this result was on the borderline of statistical significance, so we can't rule out the possibility that this is a chance finding.
While the results are interesting in helping us understand the possible causes of dementia, they don't mean that anyone who's ever felt dizzy on standing is going to get dementia.
When to seek advice
See your GP if you have frequent symptoms of low blood pressure, such as:
- dizziness or lightheadedness
- blurred vision
- heartbeats that suddenly become more noticeable (palpitations)
Where did the story come from?
The study was carried out by researchers from Erasmus Medical Centre in the Netherlands, and was funded by a range of bodies, including the Netherlands Cardiovascular Research Initiative and Erasmus University.
The Mail's headline and opening sentences overstate the study's findings, warning of "devastating implications" for people who have ever felt dizzy on standing – which is probably most of us.
BBC News gives more balanced and informative reporting, quoting one of the study's authors, who explained that the results should not worry young people with one-off episodes of dizziness on standing.
What kind of research was this?
This population-based cohort study followed a large group of people over time. Researchers wanted to see whether people who had postural, or orthostatic, hypotension (PH) at the start of the study were more likely to get dementia.
This type of study can show up links between two things, but can't prove that one factor (in this case, PH) causes another (dementia).
What did the research involve?
Researchers took a group of older people without dementia (average age 68.5) and measured their blood pressure while lying down, then within one, two and three minutes of standing, to see whether they had PH.
They followed them up until they'd been diagnosed with dementia or died, or until the end of the 24-year study. On average, each person was followed up for 15 years.
The study was part of a bigger ongoing study of people in the Netherlands called the Rotterdam Study. The researchers only looked at data on people who didn't have dementia at the start of the study and had the relevant medical tests.
Dementia was assessed using validated assessment scales: the Mini-Mental State Examination and the Geriatric Mental State Schedule. The same tests were used at follow-up.
People found to have dementia were further assessed by specialist doctors and diagnosed formally according to standard diagnostic criteria.
The researchers carried out adjustments for a wide range of confounding factors that might contribute to dementia, such as:
- blood pressure
- cholesterol levels
- other illnesses
- medicine use
- smoking history
They also measured whether people's heart rate rose as a result of standing up, and asked whether they felt dizzy or unwell.
They carried out sensitivity analyses to check whether other factors, such as people with undiagnosed dementia at the start of the study, could have affected the results.
After adjusting their figures for these potential confounding factors, the researchers calculated the chances of dementia for people with and without PH.
What were the basic results?
Of the 6,204 people in the study:
- 1,152 (18.6%) had PH, rising to 30.6% of those aged over 75
- 1,176 (18.9%) got dementia, most of whom (80%) had Alzheimer's
After taking account of confounding factors, having PH at the start of the study just increased the risk of getting dementia by 15%.
When researchers looked at just those people who had PH and had the least increase in heart rate when they stood up, they found the results were stronger – these people had an almost 40% increased risk of dementia (aHR 1.39, 95% CI 1.04 to 1.85).
However, there was little difference between people with PH who felt dizzy or unwell on standing and those who had PH but did not feel unwell. Only 13.9% of people with PH said they felt unwell.
How did the researchers interpret the results?
The researchers said their findings suggest that PH leading to repeated short episodes of insufficient blood flow to the brain plays a part in the development of dementia.
They speculated about how this happens – for example, it could be a direct result of insufficient oxygen getting to the brain causing damage to cells, or it could be to do with the automatic nervous system, which regulates blood pressure, failing to work properly.
They concluded: "OH [PH] is associated with an increased risk of dementia in the general population. This finding supports an important role for maintaining continuous cerebral [brain] perfusion [blood flow to the brain] in the prevention of dementia."
The causes of Alzheimer's – the most common type of dementia – are not well understood, despite much research.
However, we do know that factors like blood pressure, blood flow to the brain and cardiovascular health are linked to the risk of vascular dementia in particular.
In people with vascular dementia, brain scans often show up small areas of stroke where the brain has been starved of oxygen.
This study adds more weight to the idea that constant blood flow to the brain, bringing brain cells the oxygen they need, is important in maintaining a healthy brain as we get older.
But the study has some limitations, and the results are not as clear-cut as some media reports suggest.
The 15% increase in relative risk between those with and without PH is not large and was on the borderline of being statistically significant, meaning it could be a chance finding.
When the researchers split the data to look separately at the risk of getting Alzheimer's disease or vascular dementia, rather than the combined chance of getting either type, the figures were not strong enough to show a statistically significant difference.
Although the researchers took account of many factors that might have affected their results, it's possible they were affected by confounding factors not measured in the study.
For example, people with PH are more likely to experience falls and falls might cause brain injury, which the researchers speculate could increase the chances of dementia.
Dizzy spells on standing are relatively common and can be caused by dehydration, among other things. People who have repeated dizzy spells should have their symptoms checked out by a GP.
However, if you've experienced an isolated incident of dizziness on standing, especially if you're a young person, there's little to worry about.
While there's no guaranteed way to avoid getting dementia, there are some things you can do to reduce your risk:
- take regular exercise
- keep your blood pressure healthy
- don't smoke
- don't drink too much alcohol
- eat a balanced diet and keep to a healthy weight
Links to the headlines
'Dementia link to sudden low blood pressure and dizziness'. BBC News, October 12 2016
Have YOU ever felt dizzy when you stand up? Why you could be more at risk of dementia. Mail Online, October 11 2016
Links to the science
Wolters FJ, Mattace-Raso FUS, Koudstaal PJ, et al. Orthostatic Hypotension and the Long-Term Risk of Dementia: A Population-Based Study. PLOS Medicine. Published online October 11 2016
This article was produced by NHS Choices, for more stories like this visit Behind the Headlines.
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