When a dog bites a man it doesn’t make news. When a man bites a dog it makes headlines. They have a name for this kind of anomaly: Unsurprisingly, it is a “man-bites-dog” story. The following health study fits that category because it defies conventional wisdom about dementia.
Hypertension and Alzheimer’s Disease:
High blood pressure is considered an important risk factor for dementia, as well as heart disease and stroke. But a new study suggests that if blood pressure rises late in life it might actually help ward off dementia after 90 (Alzheimer’s & Dementia, online, January 16, 2017).
The 90+ Study:
Very few studies track subjects for long periods of time. Rarely do researchers study the oldest of the old. This study did both. The 90+ Study started tracking very old members of a California retirement community beginning on January 1, 2003.
By July 17, 2013, there were 1,554 people who had joined the 90+ Study. Of that number, 559 were assessed with thorough, in-person neurological exams. Various tests were administered every six months between 2003 and 2013. None of the subjects had dementia at the start of the trial. The scientists “investigated the association between age of onset of hypertension and dementia risk in an oldest-old cohort.”
Blood Pressure and Dementia:
It has long been recognized that hypertension can negatively affect blood vessels in the brain. Physicians have long been taught that elevated blood pressure will increase the risk for dementia. This has been well established for people who were diagnosed with high blood pressure in middle age.
What about people who don’t develop hypertension until they are super-senior citizens? The Adult Changes in Thought (ACT) study hinted that people who were diagnosed with high blood pressure after age 85 might have a decreased risk for dementia, though the results were not strong enough to achieve significance (Journal of the American Geriatric Society, June, 2007).
What the 90+ Study Revealed:
People who developed hypertension after their 80th birthday were 42 percent less likely to be diagnosed with dementia in their 90s. Those who developed high blood pressure after age 90 were 63 percent less likely to end up with serious cognitive decline. Hypertension was defined as blood pressure higher than 140 over 90.
Higher Blood Pressure was Protective:
Here is the man-bites-dog conclusion from the researchers:
“In this cohort study of 559 participants aged 90+, history of hypertension reported at entry into The 90+ Study was related to a lower dementia risk compared with those with no history of hypertension. This reduced risk was limited to participants who reported onset of hypertension after the age of 80 years. In addition, there was a trend for lower dementia risk with increasing severity of hypertension. These associations were independent of antihypertensive medication use.”
In essence, high blood pressure did not appear to be a risk factor for dementia at “very advanced ages” and may even be somewhat protective. The authors noted that the results from their research and “other studies in the very elderly have also found associations between hypertension and lower dementia risk.”
Why Does Higher Blood Pressure Protect the Brain?
The researchers speculate about possible mechanisms:
“The association between hypertension and reduced dementia risk in the oldest-old can be explained in several ways. First, adequate cerebral perfusion may help maintain normal cognition. Individuals who develop hypertension very late in life may be successfully marshaling a physiological compensatory mechanism to maintain adequate cerebral perfusion in the face of age-associated vascular changes. In support of this hypothesis, individuals with lower cerebral blood flow have been found to have higher rates of cognitive decline and prevalent dementia. If increased BP is a compensatory mechanism, it would also help maintain adequate perfusion in other vital organs and may explain the protective associations between increased BP and other outcomes such as mortality, frailty indicators, disability, and physical decline in the very elderly.”
In other words, higher blood pressure in very old people may help keep blood flowing to the brain so it stays adequately supplied with oxygen. The older adults in the study who had higher blood pressure were also less frail.
What To Make of This Research:
High blood pressure in middle age is associated with an increased of dementia in later years. We do not know if lowering hypertension with drugs will protect people from Alzheimer’s disease, however.
Really high blood pressure poses a risk of heart attacks, strokes and kidney damage, not to mention other vascular complications. But in this study of of octogenarians and nonagenarians, hypertension was surprisingly helpful for preserving cognitive function.
No one should EVER stop taking blood pressure medication without medical supervision. But people over 85 years of age may want to discuss the new research with a physician.