Big data reveals connection between hypertension and dementia

The link between hypertension and heart disease or stroke is well understood by doctors and many of their patients. But it’s less commonly known that high blood pressure is a significant risk factor for dementia, including Alzheimer’s disease.

Investigating this relationship has become a priority for Dr Matthew Lennon, a psychiatry registrar working with the research team at UNSW’s Centre for Healthy Brain Ageing.

Dr Lennon’s hope is that increased awareness of the dementia risk of poorly controlled hypertension will provide doctors and patients with additional motivation to diagnose, monitor and more effectively manage high blood pressure.

Dr Lennon and colleagues published a meta-analysis in 2019 that shone new light on the relationship between mid-life hypertension and Alzheimer’s disease (AD). They found the risk of AD increased by 18% and 25% respectively in people with stage 1 (≥140 mmHg SBP) and stage 2 (≥160 mmHg SBP) hypertension.

Key dementia risk factor is treatable

More recently, Dr Lennon used a large, international consortium of datasets, including more than 43,000 participants, to further investigate the effect of blood pressure and antihypertensives on dementia risk in late life.¹

The size of the data is important. As Dr Lennon explains, “Big data allows us to drill down and identify how risk factors may differ between people of different ages, sexes and racial groups. This more basic demographic data, in combination with our increasingly available large genetic datasets, allow us to be more precise in stratifying an individual’s risk of dementia, and thus be more targeted in monitoring and treatment.”

In a separate study, Dr Lennon used one of the largest genetic datasets in the world, the UK Biobank, which has more than 500,000 participants, to explore how the genetic risk for high or low blood pressure affects cognition.

These studies supported earlier findings by showing that individuals with untreated hypertension had a greater risk of both dementia (+42%) and AD (+36%) compared to those without a previous diagnosis of hypertension. Furthermore, individuals whose hypertension was effectively treated had a substantially lower risk than those who were left untreated.

Dr Lennon highlights, "It was particularly interesting to establish that the higher risk of either dementia or AD in people with untreated hypertension remained similar for individuals in their 70s and even 80s. This really does show it’s outdated to believe treating high blood pressure is less important in old age."

Opportunity for an impactful public health campaign

High blood pressure is the leading factor for preventable deaths in Australia, and is becoming more prevalent as the population ages. Historically, hypertension has been underdiagnosed and undertreated, with blood pressure control rates in Australia currently at only 32%. While guidelines for effective management are well established, compliance is poor.

Dr Lennon is hopeful that generating public awareness about this less-known risk of hypertension may change the way people think about, monitor and treat high blood pressure.

He is encouraged by a recent cross-sectional survey of Australians attending an outpatient clinic, which found dementia was the second most feared disease (after cancer).² For 29.3% of respondents this was their primary worry, four times the percentage who replied with “coronary heart disease”. As people age, their fear of getting dementia increases and, for over 65s, it is the most feared health condition.

Dr Lennon concludes, “It’s increasingly recognised that even in older patients, it’s important to keep to a target 120/80 mmHg.

Reducing blood pressure is effective for stroke prevention and heart attack. But for many people, knowing it is protective for dementia will be a greater motivator to manage this often silent but deadly disease.”

Dr Matthew Lennon received funding towards his research work through Avant’s Early Career Research Program.

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This article was originally published in Connect magazine issue 23.