Dr. Simon Mooijaart of Leiden University Medical Centre, the Netherlands, and colleagues explain that elements of the vascular system (arteries, veins and capillaries) may contribute to the development and progression of dementia.
They point out that some cardiovascular risk factors may be reversible, potentially cutting the risk of cognitive decline and dementia.
The team investigated the link between variability in blood pressure and cognitive function in 5,461 people aged 70 to 82 years living in Ireland, Scotland and the Netherlands. All were taking part in a study on the impact of statin drugs on blood vessel health, as they were at risk of cardiovascular disease. Blood pressure was measured every three months.
The well-known mini mental state examination was used to test cognitive function at the start of the study to exclude those with poor cognitive function.
After a followup of roughly three years, participants were tested on four areas of cognitive function: attention, processing speed, immediate memory and delayed memory.
“Participants with higher visit-to-visit variability in systolic blood pressure had worse performance on all cognitive tests, independent of average blood pressure,” the team reported in the British Medical Journal.
A subgroup of 553 participants underwent magnetic resonance imaging (MRI) of the brain. This showed that greater variability in blood pressure was linked to a smaller hippocampus, which is vital for memory, as well as a higher rate of cortical infarcts, a type of stroke causing difficulties reading, writing or speaking, and visual field defects.
Greater variability in blood pressure was also linked to cerebral microbleeds (small hemorrhages).
The team concluded: “Higher visit-to-visit variability in blood pressure, independent of average blood pressure and cardiovascular disease, was associated with impaired cognitive function in old age.”
It is already established that variability in blood pressure is linked to cerebrovascular damage; that is, damage affecting the blood vessels to the brain. Variability raises the risk of stroke, and possibly microvascular damage, or changes in the small blood vessels of the cerebral cortex due to damage to artery walls.
Mooijaart and colleagues say that disruption of the blood-brain barrier due to microvascular damage “results in neuronal injury and accelerates neuronal loss and brain atrophy.” In this way, higher variability in blood pressure might lead to cognitive impairment via changes in the brain structures and development of cerebral small vessel disease.
“Our findings may suggest that decreased hippocampal volume, cerebral microbleeds, and cortical infarcts are potential pathogenic mechanisms behind the association between variability in blood pressure and cognitive impairment,” they write.
In terms of preventative medication, they add, “Calcium channel blockers, the most effective drug class to reduce variability in blood pressure, show significant efficacy in lowering the risk of vascular cognitive impairment.”
They call for further work to determine whether reducing variability in blood pressure really can decrease the risk of cognitive impairment in old age.
These findings are consistent with an earlier study on 201 elderly people with a mean age of 80 years. All were at high risk of cardiovascular disease.
The researchers showed that high visit-to-visit variability in blood pressure over the course of 12 months was linked to worse performance in the mini mental state examination and global deterioration scale, widely used to measure the progression of dementia.
A separate study has looked specifically at cerebral microbleeds, which are common among the elderly population. Their impact on cognitive function is unclear. So a team from Erasmus MC University Medical Center, The Netherlands, investigated further.
They tested performance over “multiple cognitive domains” in 3,979 people aged around 60 years, without dementia.
A higher number of microbleeds were linked to worse performance on the mini mental state examination, particularly in tests of information processing speed and motor speed. Having five or more microbleeds was linked with worse performance in all cognitive domains except memory.
All of these findings emphasize the connection between healthy blood vessels and better cognitive functioning. “Once the correct treatment is in place for variation in blood pressure, this will eventually contribute to a further decline in the risk of dementia,” believes Dr. Mooijaart.
Sabayan, B. et al. Association of visit-to-visit variability in blood pressure with cognitive function in old age: prospective cohort study. BMJ, 31 July 2013 doi: 10.1136/bmj.f4600
Nagai, M. et al. Visit-to-visit blood pressure variations: new independent determinants for cognitive function in the elderly at high risk of cardiovascular disease. Journal of Hypertension, August 2012, Volume 30, pp. 1556-63, doi: 10.1097/HJH.0b013e3283552735
Poels, M. M. et al. Cerebral microbleeds are associated with worse cognitive function: the Rotterdam Scan Study. Neurology, 31 January 2012, Volume 78, Issue 5, pp. 326-33, doi: 10.1212/WNL.0b013e3182452928
Elderly woman having her blood pressure taken photo by shutterstock.