- Researchers recently investigated how age at hypertension diagnosis affects brain volume and dementia risk.
- Their results suggest people with a high blood pressure (HBP) diagnosis between ages 35 and 44 are 61% more likely to develop dementia than those without HBP.
- The team says doctors should help young adults manage HBP, given lower treatment rates in this age group.
According to the World Health Organization (WHO), around 1.28 billion people aged 30–79 worldwide have HBP, or hypertension.
HBP is the leading cause of cardiovascular disease and premature death worldwide. It is also a risk factor for diabetes, depression, and dementia.
Previous research has found that HBP before the age of 35 has associations with cognitive impairment in mid-life. Some studies also suggest hypertension in mid-life is a risk factor for dementia. However, the link between later-life hypertension and dementia is inconsistent.
While the link between hypertension, brain volume, and dementia is well-established, researchers are still not sure how the age of hypertension onset affects dementia risk.
In a recent study, researchers from China and Australia used public health data to investigate how the age of hypertension onset affects brain health and the risk of developing dementia.
“Many previous studies have demonstrated that midlife hypertension is associated with an increased risk of dementia, but whether the association of hypertension with brain volume and dementia is affected by age at diagnosis of hypertension is unclear, “ Dr. Xianwen Shang, lead author of the study, told Medical News Today.
“We found hypertension diagnosed in young adulthood or mid-life, but not late life, was associated with smaller brain volumes and an increased risk of dementia. The younger age at diagnosis of hypertension, the larger brain volume reduction was observed,” explained Dr. Shang, a research fellow at the Guangdong Provincial People’s Hospital in Guangzhou, China.
“Our findings indicate both early- and mid-life are critical periods for the prevention of dementia or brain damage via prevention and treatment of hypertension,” he added.
The authors published their study in the journal Hypertension.
Hypertension data analysis
The researchers used publicly available data from UK Biobank, a database that contains anonymous health records from around half a million people in the United Kingdom.
They included 11,399 individuals diagnosed with hypertension before receiving a brain MRI scan between 2014 and 2019. All participants entered the biobank between 2006 and 2010. The researchers split the participants into five groups according to the age they received a hypertension diagnosis:
- under 35 years
- 35–44
- 45–54
- 55–64
- over 65
The researchers then matched each individual with hypertension with a control individual who had also undergone an MRI but did not have hypertension. The team matched controls for factors including age, sex, ethnicity, income, education, cholesterol, and body mass index.
By comparing MRIs of individuals with and without dementia, the researchers found that those diagnosed with hypertension between the ages of 35 and 54 had smaller brain volumes compared with those without hypertension.
They also discovered that those diagnosed with hypertension before the age of 35 had the largest reductions in brain volume, and this difference remained significant even if these individuals later normalized their blood pressure.
Dementia data analysis
Next, to investigate dementia, the researchers analyzed health records of 124,053 individuals with HBP at baseline alongside matched individuals who did not have HBP. Over an average follow-up of 11.9 years, 4,626 people developed dementia of some type.
The researchers showed that individuals diagnosed with hypertension between ages 35 and 44 had a 61% higher risk of developing dementia than those without hypertension.
In particular, the risk of vascular dementia — a common form of dementia due to impaired blood flow to the brain — was generally higher the earlier individuals received an HBP diagnosis.
Those diagnosed before age 35 were at an 80% higher risk, while those diagnosed between 45 and 54 were at a 45% higher risk. And those aged 65 years or older were at only a 2% higher risk.
However, the researchers found there was no relationship between hypertension diagnosed at any age and the risk of Alzheimer’s disease.
Underlying mechanisms
“There are several mechanisms for the effects of hypertension on the risk of dementia,” said Dr. Shang. “Firstly, hypertension is a well-known primary cause of stroke resulting in an increased risk of dementia, especially vascular dementia.”
“Secondly, a continuous supply of oxygen and glucose from blood to the brain is fundamental for brain and cognitive health. Increased motor stiffness and reduced compliance caused by long-term exposure to hypertension may reduce cerebral blood flow and increase cerebrovascular reactivity, thus resulting in brain damage or cognitive decline,” he added.
“The exact mechanism underlying the link between HBP and dementia risk is unknown and was not the focus of this study,” Dr. Simin Mahinrad, Ph.D., told MNT. Dr. Mahinrad is a research assistant professor at Northwestern University’s Feinberg School of Medicine in Chicago, IL, and was not involved in the study.
“However, it is generally believed that interactions between several pathologic factors are most likely responsible. Importantly, hypertension may result in structural and functional alterations in cerebral vessels, such as atherosclerosis, vascular stiffness, vascular remodeling, and impaired cerebral blood flow circulation and regulation.”
– Dr. Mahinrad
“Such alterations in cerebral vessels predispose the brain to several pathologies, such as white matter damage, brain volume loss, deposition of pathologic proteins, and stroke. All of these pathologies have been shown to affect cognitive function negatively and increase the risk for dementia,” Dr. Mahinrad continued.
MNT also spoke with Keenan Walker, Ph.D., from the Laboratory of Behavioral Neuroscience at the National Institute on Aging, who was not involved in the study. He said:
“Chronic hypertension, especially if untreated, may cause damage to the small vessels, which deliver blood to the brain, making them less efficient and reactive to systemic changes in blood pressure.”
“In this way, hypertension may lead to changes in cerebral blood flow, limiting the brain’s ability to deliver the necessary oxygen and nutrients. [The] age at which hypertension begins and the duration of hypertension seem to matter. Those who have hypertension begin earlier in life will likely have much more exposure to the adverse effects of HBP on end organs, such as the brain.” he added.
The researchers conclude that their findings highlight the importance of age during a hypertension diagnosis in the link between hypertension, brain volume, and dementia.
They say scientists should focus more on managing blood pressure among young adults given high levels of unawareness and lower treatment rates in this age group.
Limitations
The researchers explain that their study cannot prove a causal relationship because of its observational design.
They also say that early dementia can begin decades before diagnosis and, therefore, before a hypertension diagnosis. With this in mind, scientists need to conduct more research to confirm the relationship between dementia and the age of hypertension diagnosis.
“Whether hypertension diagnosed at a younger age is associated with a larger decrease in brain volumes remains to be explored in studies with brain structure measured at multiple time points.”
– Dr. Shang
Another issue is that determining when healthcare professionals diagnosed hypertension relies on participant memory. As Dr. Walker explained:
“This is subject to inaccuracies, and a proportion of participants may have gone with undiagnosed hypertension for some time. Another limitation is the inability [to] differentiate Alzheimer’s dementia from vascular dementia with a high degree of accuracy. Biomarkers would have been helpful for this purpose,” he added.
Dr. Mahinrad explained another limitation: “The effect of antihypertensive treatment on the results has not been reported. This is important because antihypertensive drugs are known to affect neurocognitive measures, and their impact on brain volume within the context of [the] study is unknown.”
Dr. Mahinrad also explained that “the generalizability of these results to other populations with different ethnic backgrounds remains unknown.”
Strengths and the future
“This study has several strengths: a population-based study of a large number of individuals — around 20,000 participants — in the U.K., [the] inclusion of both males and females, rigorous statistical analyses to minimize sources of bias, and use of fully automated quantitative MRI data,” said Dr. Mahinrad.
Dr. Shang added, “Future longitudinal studies with longer follow-up duration are needed to examine whether hypertension diagnosed at a younger age was associated with a larger excessive relative risk of dementia over two or more decades.”
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