Researchers say the findings are just as concerning for systolic blood pressure below 120mmHg treated with antihypertensives.
About one in two people (47%) in Australia aged 75 and over have high blood pressure, which is a major risk factor for chronic conditions including heart failure and kidney disease.
But new research from the Centre for Healthy Brain Ageing (CHeBA) at the University of New South Wales adds to the evidence base that hypertension, when left untreated, can also be significantly associated with cognitive decline in older people.
Using data from the Sydney Memory and Ageing Study, researchers compared the cognitive outcomes of 1015 people without dementia, aged 70–90, who were assessed over a six year period. They were divided into three distinct systolic blood pressure groups: ≤120 mmHg, 121–140 mmHg, and >140 mmHg.
Researchers found that the group of participants with systolic blood pressure reading greater than 140 mmHg and who did not use antihypertensives had rates of cognitive decline of 0.40 – approximately double the average decline of participants over the course of the study.
The cohort with a systolic blood pressure reading of less than 120 mmHg who were being treated with antihypertensive medications also had a worse cognitive trajectory.
‘Over the course of our study they had approximately doubled the rate of cognitive decline compared to the average participant,’ lead author Dr Matt Lennon said.
The findings have raised questions over the American Heart Association’s controversial decision in 2017 to lower the definition of hypertension, recommending that blood pressure be maintained below 120/80mmHg.
In contrast, the National Heart Foundation of Australia’s 2016 Guide to Management of Hypertension in Adults, endorsed by the RACGP, is more cautious. It classifies 120–129 mmHg as normal, and 130–139 mmHg as high normal.
Co-director of CHeBA and co-author of the paper, Professor Perminder Sachdev told newsGP the research raises questions about what the systolic blood pressure targets should be in older populations.
‘High blood pressure is very common in the older population and there have been many recommendations over the years in terms of what the target blood pressure should be,’ he said.
‘The [American Heart Foundation’s] recommendation was based on the fact that people with this lower target had reduced cardiovascular incidence and mortality, and renal disease. The question, of course, is does this apply to the older population as well?’
Professor Sachdev said the concern relates to the stiffening of arteries that can occur in older age, reducing pulsatility.
‘So actually, to maintain perfusion, you may need a higher systolic blood pressure,’ he said.
Professor Nicholas Zwar is a GP and member of the National Heart Foundation of Australia’s National Blood Pressure and Vascular Disease Advisory Committee.
He told newsGP the research supports Australia’s targets and is an ‘an interesting addition’ to the literature linking elevated blood pressure to the risk of dementia.
‘In general terms, the Australian approach is probably pretty consistent with what this article is finding,’ Professor Zwar said.
‘Less than 140/90 mmHg is the general target and the current guidelines … say you may aim for lower blood pressure in selected patients. Those are people at high absolute cardiovascular risk, where it’s deemed safe on clinical grounds and where drug therapy is well tolerated.
‘So it’s not saying aim for lower targets in everyone.’
However, this does pose a challenge, Professor Zwar said, that requires clinical judgement.
Study co-author Professor Perminder Sachdev says the research raises questions about systolic blood pressure targets in older populations.
‘The problem, of course, is that as people get into very old age, everyone is at high cardiovascular risk because absolute risk is very much driven by age,’ he explains.
‘So older people would be at high risk, but in many cases their treating doctor may not feel it safe to try for a lower target because they’d be worried about postural hypotension or acute kidney injury, [as] they’re probably the two biggest risks of going for a lower target.
‘I think GPs are also conscious of the lack of evidence about treatment in the very old, because many of the studies don’t include really elderly people. So the outcomes of treatment on blood pressure in the elderly are less clearly established than in younger people, though that is changing as more older people are included in trials.’
Hypertension is one of the most prevalent risk factors for cognitive decline, and dementia is the second leading cause of death in Australia behind coronary heart disease. Yet despite the links, Professor Sachdev says clinical trials are lacking.
‘One of my gripes is that cardiologists don’t talk to neurologists and vice-versa, even though much of brain health is heart health; the vascular system is the same,’ he said.
‘The risk factors for heart disease are shared by dementia to a significant degree. So we should be talking to each other, and our trials should include each other.’
Professor Zwar agrees.
‘The outcomes that are highlighted or tend to get greatest attention in studies of cardiovascular disease and treating blood pressure are all cause mortality and cardiovascular events or cardiovascular mortality,’ he said.
‘Cognition is, I agree, not as often measured and certainly not as prominent in the outcomes that are focused on as important.’
Despite this, he says GPs tend to take a ‘holistic view’ when treating blood pressure.
‘That’s not only reducing the risk of stroke or other vascular event, it’s also the possible adverse effects of treatment, including postural hypotension, kidney injury and cognitive effects,’ Professor Zwar said.
In light of the research, Professor Sachdev says GPs should aim for that ‘sweet spot – if there is one’.
‘It is really important to control high blood pressure because it is one of the most important risk factors for dementia that is modifiable,’ he said.
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