In what could be a major development in the study of dementia and other cognitive impairments, an American study has found that among those with hypertension, intensive systolic blood pressure control can reduce the likelihood of mild cognitive impairment, which often leads to dementia.
Part of the wider SPRINT trial (Systolic Blood Pressure Intervention), the randomised clinical trial was conducted at 102 sites in the US and Puerto Rico among adults aged 50 years or older.
According to the Heart Foundation, as of 2014/15, close to 6 million Australians (34 per cent) aged 18 or over had high blood pressure (systolic blood pressure 140mm Hg or over) with the percentage creeping up to 41.5 per cent for over 65s.
The trial looked at the effect of intensive blood pressure control treatment (systolic blood pressure of 120mm Hg or less) on the probability of dementia and mild cognitive impairment in comparison with those treated with a blood pressure goal of 140mm Hg or less (standard treatment group), as previous observational studies have shown that hypertension (which effects 35 per cent of Australians over 55) is a risk factor for both conditions.
During a total median follow-up of 5.11 years, adjudicated probable dementia occurred in 149 participants in the intensive treatment group vs 176 in the standard treatment group (7.2 vs 8.6 cases per 1000 person-years). Intensive blood pressure control significantly reduced the risk of mild cognitive impairment (14.6 vs 18.3 cases per 1000 person-years) and the combined rate of mild cognitive impairment or probable dementia (20.2 vs 24.1 cases per 1000 person-years).
The study had some drawbacks. Firstly, it was stopped early for ethical reasons: as the benefits of dropping blood pressure below 120 had such a positive effect on the likelihood of cardiovascular events and death, the researchers felt that those being treated at the higher blood pressure rate needed to be informed.
Furthermore, in her editorial on the paper, Dr Kristine Yaffe from the University of California, San Francisco, wrote that information to compare the effects of different classes of antihypertensive drugs on cognitive outcomes were not provided, and that questions remain as to what age is best to treat elevated systolic blood pressure and whether the same care should be administered to all ages. Yaffe also noted that as participants who had diabetes, stroke or symptomatic heart failure were excluded from the trial, the findings cannot, at this stage, be generalised.
However, Yaffe found the study to be an overall positive step in finding a dementia prevention.
“For older adults, almost all of whom have concern about being diagnosed with Alzheimer’s disease and related dementia, SPRINT MIND offers great hope. The study demonstrates that among those with hypertension, intensive systolic blood pressure control can reduce the development of cognitive impairment,” she said.
Yaffe added: “The SPRINT MIND study may not be the final approach for prevention of Alzheimer’s disease or other cognitive impairment, but it represents a major leap forward in what has emerged as a marathon journey.”
Associate professor Gideon Caplan, director of geriatric medicine at of the Prince of Wales Hospital in Sydney said: “It’s a very exciting result, being the first study to show an effect caused by lowering blood pressure on cognitive function.
“Its not a ‘slam dunk’ result,” he warns, “because there was no significant effect of intensive blood pressure control on dementia, but intensive blood pressure control did reduce mild cognitive impairment and the combined outcome of mild cognitive impairment and dementia. But the study did stop early because of the positive effect on cardiovascular events.
“This builds on what we already knew, that vascular risk factors, like high blood pressure and smoking are associated with more frequent dementia,” he said.
Senior research scientist at NeuRA, Dr Ruth Peters, thinks that this study, one of a number of similar trials looking at cardiovascular issues with dementia as the secondary concern, is the best yet.
“It’s the strongest finding yet, and it adds to an existing body of literature, and existing series of trials that point in the same direction. So, it’s quite promising,” she said.
As to whether doctors should now advise reducing blood pressure with mild cognitive impairment in mind, Peters is cautious, saying that “we already know that reducing blood pressure reduces cardiovascular events, so we should be doing it anyway. The exact goal depends on the particular characteristics of the patient.”
As to next steps, Peters thinks a study that focuses solely on the question of mild cognitive impairment and dementia should be next.
“We really need now to definitively look at this question of blood pressure and dementia in a trial designed to look at that,” she said.
She also believes that study must look at those parts of the populations yet to be considered, such as looking at different racial characteristics and those for whom it may potentially be riskier to lower blood pressure, as in the case of people with orthostatic hypotension.
“We need to know more about the higher risk population. We need to know more about the age ranges, younger adults,” she said.
“What happens if you have high blood pressure below 50? We know your dementia pathology may start to be accrued decades before you develop the symptoms … so, the next questions are around the populations we haven’t studied yet.”
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