Cross sections of a normal brain and a brain damaged by advanced Alzheimer's… (Merck & Co. )
Beta blockers, a venerable class of blood pressure drugs that has fallen from favor in recent years, may help protect the aging brain against changes linked to Alzheimer's disease and other forms of dementia that rob memory and mental function, new research indicates.
In autopsies on the brains of 774 men after their deaths, scientists found that those who took beta blockers to help control hypertension had fewer of the brain lesions and less of the brain shrinkage seen in Alzheimer's than men who took other types of blood pressure medications and those who left the condition untreated. Their brains also showed significantly less evidence of multiple tiny strokes, called microinfarcts.
A parallel study showed that an expanded group of men who took beta blockers also experienced less cognitive decline as they aged compared with those in the control groups.
The research, to be presented at the American Academy of Neurology's annual meeting in March but released to the media on Monday, is preliminary; of the 774 Japanese American men who agreed to have their brains examined after death, 610 had suffered from high blood pressure and only 40 had taken beta blockers.
That is far too small a number to support a sweeping conclusion that beta blockers have benefits beyond controlling high blood pressure, experts warned.
"There's a hint there," said Dr. Charles DeCarli, director of the Alzheimer's Disease Center at UC Davis, who was not involved in the study. If borne out by further research, including a clinical trial, the findings could give physicians a powerful tool for preventing dementia and induce many more Americans to get their blood pressure under control, he said.
The study adds to mounting evidence that high blood pressure has a corrosive and probably cumulative effect on the brain, and that treating it promptly and effectively can yield dividends beyond lowering the risk of heart attack or stroke. Studies suggest the risk of Alzheimer's and other dementia is lower for people whose blood pressure is kept within healthy bounds.
The newest study suggests that the 11 classes of drugs used to lower high blood pressure do not confer equal protection against dementia. "Beta blockers are different," said Dr. Lon White, a University of Hawaii neurologist who led the study, which has not yet been published in a medical journal.
Americans filled 161 million prescriptions for beta blockers in 2011, making them the sixth most commonly dispensed prescription drug in the United States, according to IMS Health. In addition to suppressing the rate at which the heart pumps blood, beta blockers can cause fatigue, impotence, depression and insomnia. As a result, they have progressively lost ground to newer classes of drugs with fewer side effects.
White suggested that by lowering the heart rate, beta blockers may reduce wear and tear on small blood vessels throughout the body, including those that carry oxygen and fuel to every corner of the brain. Fed by healthier vessels, the aging brain would be less likely to suffer microinfarcts.
Because the loss of cells is small and scattered throughout the resilient brain, the toll on cognition may not be evident immediately, White said. But eventually the brain can be riddled with lesions, a condition called vascular dementia. And they may accelerate the early brain changes of Alzheimer's, he said.
In microscopic examination of his subjects' brain tissues, White said, he found significantly fewer microinfarcts in those who had taken beta blockers.
"This is a tantalizing clue," he said.
DeCarli suggested another way in which healthier small blood vessels in the brain could help prevent or slow degenerative changes that come with Alzheimer's: Vasculature may be instrumental in clearing abnormal proteins from the brain, and where it has been damaged by the cumulative effects of hypertension, the tiny vessels may no longer be up to the job of keeping the stalking horses of Alzheimer's from accumulating.
Almost 3 in 10 American adults — 28.6% in 2010 — have high blood pressure, according to the Centers for Disease Control and Prevention. About 46% of those thought to suffer from the condition either have not been diagnosed or have taken no measures to control it.
"We know there's a connection between heart health and brain health," said Heather Snyder, who helps oversee research grants at the Alzheimer's Assn. in Chicago. Until researchers have better evidence to guide decisions on which blood pressure medications might help the brain, she said, people should protect their hearts in ways that have already been well demonstrated: by getting enough exercise, maintaining a healthy weight and keeping blood pressure and cholesterol numbers within a healthy range.