BY LIZETTE BORRELI
Elevated blood pressure was associated with lower gray matter volume in young adults, according to a German study published online on January 23 in Neurology.
In individuals age 40 years or younger, those with blood pressure levels above 120/80 mmHg, but who are not considered hypertensive, had lower brain volumes in regions associated with gray matter decline in older individuals with hypertension.
The researchers, led by Lina Schaare, PhD candidate, department of neurology, Max Planck Institute for Human Cognitive and Brain Sciences in Leipzig, Germany, believe the results "highlight the importance of taking BP levels as a continuous measure into consideration, which could help initiate such early preventive measures."
Previous studies have looked at specific brain structures and found a link between hypertension and reductions in brain volume in the medial temporal lobe and other regions. Elevated blood pressure in midlife also has been linked to lower brain volume on autopsy and increases in the tangles and plaques associated with Alzheimer's disease in the hippocampus. But the effects of elevated blood pressure on the brains of individuals age 40 or younger are unclear.
To find out whether elevated blood pressure levels are associated with lower gray matter volume in brain regions, specifically in the frontal and medial temporal lobes, the researchers assessed four unpublished datasets of studies conducted in Germany between 2010 and 2015.
The team identified 423 participants, average age 27.7 years; 42 percent women, who had not been previously diagnosed with hypertension.
They measured systolic blood pressure (SBP) and diastolic blood pressure (DBP) at varying times of day. The researchers then took the average of these multiple measurements to one average systolic and one average diastolic reading for each participant.
Using the 2013 European guidelines for the management of arterial hypertension, they classified participants based on blood pressure levels: individuals in category 1 had SBP < 120 mmHg and DBP < 80 mmHg; category 2 had SBP 120-129 mmHg or DBP 80-84 mmHg; category 3 had SBP 130-139 mmHg or DBP 85-89 mmHg; and category 4 had SBP ≥ 140 mmHg or DBP ≥ 90 mmHg.
All participants had at least one blood pressure reading: 41 percent had blood pressure lower than 120/80 mmHg (defined as normal); 29 percent had blood pressure between 120/80 to 129/84; 19 percent between 130/85 and 139/89; and 11 percent above 140/90 (defined as hypertension in the European study).
The researchers used a statistical mapping technique to detect small differences between volumes in brain regions on MRI scans.
The findings revealed increases in SBP (above 120/80 mmHg) was linked to lower gray matter volume in the hippocampus, amygdala, thalamus, frontal, and parietal structures.
Meanwhile, increases in DBP were associated with lower gray matter volume in the bilateral anterior insula, frontal regions, right midcingulate cortex, bilateral inferior parietal areas, and right superior temporal gyrus.
Differences in gray matter volume were seen among people with blood pressure less than 120/80 mmHg and those with the next two levels of elevated blood pressure.
No significant associations were identified between elevated blood pressure and total brain size.
The findings only show an association, not causality between lower brain volumes and hypertension. The exact mechanism behind the association remains unknown. But, the researchers emphasized, "it has been proposed that medial temporal (and frontal regions) might be especially sensitive to effects of pulsation, hypoperfusion, and ischemia, which often result from increasing pressure."
Further research is needed to observe whether gray matter volume changes in young age could increase the risk for stroke, dementia, and other diseases later in life.
The Max Planck Institute for Human Cognitive and Brain Sciences supported the study.
The researchers reported no conflicts of interest.
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Schaare HL, Masouleh SK, Beyer F, et al. Association of peripheral blood pressure with gray matter volume in 19- to 40-year-old adults. Neurology 2018; Epub 2018 Jan 23.