Multiple non-genetic factors contribute to the development of cognitive decline and dementia

The next time you find yourself forgetful, do not pass it off as part of aging. While it is commonly believed that memory loss is an inevitable consequence of aging, medical research has provided physicians with evidence that this deterioration can be reduced and even reversed when appropriate measures are taken.

Blood pressure and cognitive decline

The development of high blood pressure in midlife appears to be an important risk factor for the development of dementia later in life. The presence of poorly controlled high blood pressure is associated with cognitive decline .Prolonged elevation of blood pressure leads to thickening of the blood vessel wall and cause narrowing of the lumen of the microscopic vessels in the brain.  Multiple studies on blood pressure lowering in the middle aged showed that blood pressure lowering decreased the incidence of dementia.

In the well designed Syst-Eur trials, the results show that the treatment of 1000 high blood pressure patients for 5 years can prevent 20 cases of dementia .This benefit is also seen in those with prior strokes. For those with prior stroke, the Perindopril Protection Against Recurrent Stroke Study (PROGRESS), showed that there was a reduction of incident dementia or cognitive decline when blood pressure was reduced. It is less certain how the development of high blood pressure in the very elderly affects the development of high blood pressure.

While studies on the lowering of blood pressure in the very elderly had mixed effects on cognitive function, it was nevertheless consistently associated with lower risk of stroke and heart attacks. Part of the reason could be that these studies were for too short a period for benefits on cognitive function to be seen.

The benefits of blood pressure lowering were particularly seen in certain classes of blood pressure lowering drugs.   In 2013 Neurology  journal publication on the subsequent analysis of the Ginkgo Evaluation of Memory Study (GEMS ) study, a six-year effort to determine if  use of the herb ginkgo biloba reduced dementia risk, a study team led by researchers from John Hopkins found that people over the age of 75 with normal cognition who used blood pressure drugs such as diuretics, angiotensin-1 receptor blockers (ARBs) and angiotensin-converting enzyme (ACE) inhibitors showed a reduced risk of Alzheimer dementia by at least 50%. Beta blockers and calcium channel blockers did now show a link to reduced risk in this study.Hence, the selective choice of blood pressure drugs can provide incremental benefit for reduction of dementia risk.

Interestingly, a 1996 Swedish study published by Guo in British Medical Journals showed that those with a SBP of 140 or less mm Hg and DBP of 75 or less mm Hg were significantly more likely to have dementia. However, this may be explained by the impaired neural blood pressure regulatory system in those with Alzheimer dementia, which may result in low blood pressure and postural drop in blood pressure.  Hence, it is not low blood pressure that causes dementia but dementia that may result in low blood pressure.

Is a fast heart rate detrimental?

The question that is often asked is that if the resting heart rate is high, is there a detrimental effect on health. In the Prevention Regimen for Effectively Avoiding Second Strokes (PRoFESS) study, those with prior stroke who had a  higher heart rate of more than 67/min had an accelerated decline in cognitive decline.  The findings suggest that a low heart can reduce the size of the stroke rather than reducing the likelihood of a second stroke.  The data suggests that high heart rate may be considered as a risk factor for cognitive decline and dementia.  It has also been observed that patients with Alzheimer’s dementia had  a higher heart rate when compared with controls.

Sleep disturbances

Patients who snore or sleep with their mouths open are likely to have decrease in the oxygen saturation in their blood while they sleep, resulting in oxygen “starvation” of the brain during sleep. This is also termed as sleep apnoea and can be diagnosed with a sleep test. Chronic oxygen deprivation during sleep can result in reduction of brain volume and damage to the brain.  This damage to the brain appears as white patches on a magnetic resonance scan of the brain and are referred to as white matter hyperintensities (WMH). Decrease in brain volume and progressive increase in WMH are associated with cognitive decline and dementia. This oxygen deprivation is due to obstruction of the nasal passages and/or obstruction of the upper airway and can be relieved by appropriate treatment.  Studies have also shown that those with decreased brain volume and memory impairment who are given sufficient oxygen therapy continuously during sleep for 3 months have an increase in brain volume and improvement in cognitive testing.  While most will expect to see such changes in the elderly, these changes can appear in those as young as forties. Hence, if you snore, sleep with your mouth open and constantly feel tired despite adequate hours of sleep, it is highly likely that your brain is not getting sufficient oxygen when you sleep.  Taking proactive measures to diagnose the problem and address the airway obstruction can help to reduce the likelihood of cognitive decline.

Strokes

Strokes can cause significant cognitive decline.  Risk factors for stroke include high blood pressure, diabetes mellitus, high cholesterol and smoking.  These risk factors are easily identified and can be treated to reduce the risk of stroke.  However less apparent and a relatively common cause of stroke in the elderly is the abnormal heart rhythm termed as atrial fibrillation (AF) .  It is estimated that for those 65 years and above, about one in ten has AF.  In AF, there is a “short circuit” of the electrical system in the upper heart chambers resulting in a heart rate of about 400 per minute.  The resultant effect is that the upper chambers are “quivering” rather than pumping normally.  Hence, blood entering the left upper chamber will slow down considerably and this increases the risk of blood clot formation.  If a blood clot forms, it can potentially be pumped out of the heart into the brain circulation, block a major brain artery and cause a massive stroke. Hence, if you have frequent palpitations and the pulse is irregular, it may be due to AF and you should get your heart assessed by a heart specialist.

A physician I was speaking to a week ago related to me that he had a stroke following an invasive test that involved the insertion of a plastic tubing into his arteries and the injection of contrast into the heart arteries, a procedure called coronary angiography. When a plastic tubing is inserted especially through the right wrist artery, the tubing has to pass through a major neck artery which leads directly into the right side of the brain. If there are cholesterol plaques in the wall of the major neck artery, the tip of the tubing can potentially damage the lining of the arterial wall and result in the release of cholesterol debris into the arterial lumen and follow the blood flow into the brain. The cholesterol debris can occlude a brain artery and cause stroke. He expressed that he was glad that there were now safer alternatives such as computed tomography (CT) scan of the heart arteries which can be performed safely within seconds and allow 3 dimensional visualisation of the heart arteries. Minor “silent “ strokes from invasive procedures such as coronary angiography, reported to occur in 5% to 22% in at least 7 prospective studies, can contribute to the development of dementia. Hence, whenever you are asked to undergo a test that involves the insertion of a tube into arteries in the vicinity of the neck arteries, you should always discuss with your physician about a safer non-invasive alternative.

Age wisely

Cognitive decline is not an inevitable consequence of aging.  Multiple non-genetic factors contribute to the development of cognitive decline and dementia.  Early recognition of the risk factors or conditions that can predispose to the development of cognitive decline will enable one to take proactive measures to age wisely.