People who frequently feel dizzy on standing 'at future risk of dementia'

"Middle-aged people who feel dizzy when standing up from a lying-down position may be at a higher risk of dementia or a stroke in the future," reports BBC News, after researchers followed a large group of people in the US for up to 25 years.

The study looked at postural hypotension – where a person's blood pressure drops if they quickly stand up from either lying down or sitting. It can make people feel dizzy and increase their risk of fainting or falling over.

The researchers looked at more than 11,000 middle-aged adults who were tested for postural hypotension in the late 1980s. These people were followed up until 2013 to see if they developed dementia or had a stroke.

People who had postural hypotension were around 1.5 times more likely to go on to develop dementia and twice as likely to have a stroke than those who did not have postural hypotension.

However, we cannot be certain that postural hypotension directly caused these increases in risk.

Postural hypotension can have a wide range of causes, such as heart disease, and is also a side effect of high-blood-pressure medications. Both heart disease and high blood pressure are risk factors for dementia, specifically vascular dementia, which is caused by reduced blood flow to the brain.

Most people will occasionally experience postural hypotension, especially if they have been sitting or lying down for some time.

But if you find yourself experiencing frequent episodes, you should see your GP. This dizziness could be a symptom of another, treatable condition.

Where did the story come from?

The study was carried out by researchers at Johns Hopkins Bloomberg School of Public Health, Oregon State University, Harvard Medical School's Beth Israel Deaconess Medical Center and a number of other US universities.

It was funded by the US National Heart, Lung, and Blood Institute and published in the peer-reviewed journal Neurology.

The BBC News headline – "Dizziness when getting up could increase dementia risk, US study says" – is misleading.

It's understandable the BBC would want to avoid complex terms such as "postural hypotension" in a headline, but the study results do not apply to everyone who has ever been dizzy or lightheaded on standing.

Also, although the study found that postural hypotension was linked to dementia risk, the research did not show that it was a direct cause, as implied in the headline.

The Mail Online's claim that "feeling lightheaded when standing up could be a warning sign of dementia" also had the potential to confuse. It suggests that lightheadedness indicates a person already has dementia, rather than having an increased risk in the future.

However, headlines aside, the media generally did a good job of summarising the research and its findings.

What kind of research was this?

This was a cohort study looking at data from the Atherosclerosis Risk in Communities (ARIC) study, which started in the 1980s.

Postural hypotension, also called orthostatic hypotension, is where a person's blood pressure drops when they suddenly stand up from lying or sitting.

This drop in blood pressure can lead to dizziness or fainting because blood flow to the brain is reduced, and people can fall and injure themselves as a result.

However, postural hypotension is a symptom rather than a disease and can be caused by a number of different conditions.

Researchers were interested in looking at whether postural hypotension might affect brain function and risk of stroke or dementia in the long term, as previous studies have not given a clear answer.

Although cohort studies are good for assessing the effects of risk factors over a lifetime, this particular piece of research had the limitation that it only measured postural hypotension at the start of the study and never again.

This means we do not know whether people who had postural hypotension at the start of the study were successfully treated and it was no longer a problem. We also do not know whether people without postural hypotension at the beginning of the study went on to develop it later.

What did the research involve?

Researchers used data from the ARIC study, which recruited middle-aged people from 4 regions in the US and monitored them over a number of years. They were initially recruited to the study from 1987 to 1989, and then invited back for 4 more visits over the period up to 2013.

For the present study, the researchers excluded anyone who had a previous history of heart disease, stroke or Parkinson's disease, or who did not have the information the researchers needed recorded across the study.

Postural hypotension was measured only at the first assessment. People were asked to lie down for 20 minutes, and had a series of blood pressure measurements taken before and after they stood up.

People were classed as having postural hypotension if they had a drop in systolic blood pressure (the first, higher number in a blood pressure reading) of at least 20mmHg or a drop in diastolic blood pressure (the second, lower number in a blood pressure reading) of at least 10mmHg when they went from lying down to standing.

The researchers used a number of methods to identify which study participants developed dementia.

In some cases, they were able to invite people for examination, while in others they contacted the person or someone associated with them to ask if they had received a diagnosis of dementia. In some cases people's electronic medical records were used.

They used similar methods to find out if people had gone on to have a stroke.

For the analysis, the researchers also took into account other confounding factors that could influence a person's later risk of dementia and stroke – such as age, gender, ethnicity, drinking and smoking habits, and whether they had diabetes, high blood pressure or high cholesterol.

What were the basic results?

The study included a total of 11,709 people with an average age of 54 when they enrolled.

At the start of the study, 552 people (4.7%) had postural hypotension. During a follow-up period of up to 25 years, 1,068 people developed dementia and 842 had a type of stroke caused by reduction of blood flow to part of the brain.

Overall, people with postural hypotension at the start of the study were no more likely to have a decline in their mental function than people who did not have it, after other factors were taken into account.

However, dementia was about 1.5 times more common in people who had postural hypotension at the start of the study than in those who did not (hazard ratio [HR] 1.54, 95% confidence interval [CI] 1.20 to 1.97).

People with postural hypotension at the beginning of the study were also about twice as likely to go on to have a stroke (HR 2.08, 95% CI 1.65 to 2.62).

How did the researchers interpret the results?

The researchers noted there was an association between postural hypotension in middle age and risk of dementia or stroke in later life, even after taking into account some of the other factors that influence health in later life.

They acknowledged, however, that they were not able to account for all the possible things that could have influenced the findings. For example, they were not able to monitor whether people took medication to treat the condition or see what effect this had over time.

They said that further research would be needed to understand the way in which postural hypotension might contribute to increased risk of dementia and stroke, and ways in which any risks might be reduced.

Conclusion

This was a large and reasonably well-conducted study that highlighted a possible association between a symptom people may experience in middle age and their risk of developing dementia or stroke in later life. But it does not tell us why they might be linked.

Because postural hypotension was only measured at the start of the study, we do not know whether people continued to experience it over time, if they were successfully treated, or if some only developed it later. We also cannot tell if it mattered how long someone had postural hypotension or what had caused it.

Another limitation is that the study may not have managed to find everyone who developed a stroke or dementia. Ideally, all participants would have been assessed directly by the researchers to confirm whether or not they had these conditions.

Overall, while this study is likely to prompt further research into whether and why such a link exists, the findings are not conclusive.

If you experience frequent dizzy spells, you should make an appointment with your GP, as this might need investigating.