What we know about blood pressure when it comes to brain health is that it is a Goldilocks phenomenon. By that I mean that there is a range that is “just right”.
Erring either side of this – with high blood pressure (hypertension) or low blood pressure (hypotension) – is not ideal.
The problem with your blood pressure being too low is that the brain may not receive the supply of nutrients and oxygen that it needs over a given period.
Given that the brain is the most energy hungry organ in the body (constituting 25 per cent of the body’s energy requirements), low blood pressure can have significant effects on brain function and cognitive performance.
It is likely that this is more pronounced the older you are as your brain tends to be more vulnerable to physiological changes with age.
Worryingly, if the pressure is too low for too long, this can cause permanent damage to the brain as neurons “starve” and potentially die.
We know there is an association between low blood pressure and dementia, though this is complicated by the fact that dementia itself may damage the centres of the brain responsible for maintaining adequate pressure.
It’s therefore a bit of a chicken-and-egg scenario.
So, what causes your blood pressure to be too low?
Some reasons are obvious: Significant blood loss reduces the volume of blood circulating in the body and brain, and hence lowers the pressure.
More commonly, dehydration is the culprit, again because the volume of blood is reduced (90 per cent of blood is water). This is a real issue in summer especially.
Problems affecting the heart – heart attacks and heart failure – don’t help, and even conditions affecting other organs can be a problem, particularly the adrenal glands above the kidneys.
Medications and severe infections are other not uncommon causes.
When it comes to high blood pressure and the brain, there are two main risks.
One is if your blood pressure acutely becomes very high and results in a stroke; the other comes from have persistently elevated blood pressure above the norm.
Over time, this can be deeply damaging to the brain and is unequivocally associated with an increased risk of dementia – both vascular dementia (due to altered blood supply) and Alzheimer’s disease.
The causes of high blood pressure are myriad.
Acute stress can temporarily increase your blood pressure directly, through the release of stress hormones such as cortisol and adrenaline.
It is less clear whether stress directly induces more persistent changes in blood pressure, but people who are stressed often sleep poorly, eat unhealthily (fat and salt being especially problematic) and stop exercising, all of which do raise blood pressure.
Drinking too much alcohol also increases blood pressure over the longer term. Diabetes is a risk, as is kidney disease and obesity.
So, what pressure should you be aiming for? Well, this is definitely something to discuss with your doctor – as individual needs may differ – but anything above 130/80mmHg is considered high blood pressure.
There is even research suggesting that high normal blood pressure – just below 130/80mmHg – although not officially high blood pressure, is probably not optimal, with higher values being associated with increased brain shrinkage.
Like many factors for brain health, you have agency over your blood pressure, so make sure you live a life that helps you control it and discuss it in a timely fashion with your GP.
Kailas Roberts is a psychogeriatrician and author of Mind your brain The Essential Australian Guide to Dementia now available at all good bookstores and online. Visit yourbraininmind.com or uqp.com.au