March 9, 2021
Blood pressure typically varies over the course of 24 hours, and is typically lower at night than during the day. But people whose blood pressure is typically higher during the evening hours than during the daytime may be at increased risk for Alzheimer’s disease, a new study reports.
For the study, researchers at Uppsala University in Sweden followed nearly 1,000 older Swedish men for up to 24 years, beginning when they were in their early 70s. At the start of the study, all were free of Alzheimer’s disease or other forms of dementia.
Compared to men whose blood pressure went down in the evenings, those with higher blood pressure at night were 1.64 times more likely to develop Alzheimer’s disease. The findings were published in the journal Hypertension.
It is possible that high blood pressure at night may inhibit the brain’s ability to clear waste products during sleep. Buildup of these waste products in the brain may set the stage for Alzheimer’s disease onset, some research suggests.
“The night is a critical period for brain health,” said the study’s senior author Christian Benedict, an associate professor of neuroscience at Uppsala. “In animals, it has previously been shown that the brain clears out waste products during sleep, and that this clearance is compromised by abnormal blood pressure patterns. The night also represents a critical time window for human brain health.”
Higher nighttime blood pressure readings, a pattern known as “reverse dipping,” is seen in a variety of medical conditions, including hypertension and Type 2 diabetes. It also occurs in sleep apnea, in which breathing stops for brief periods during the night. All those conditions are tied to an increased risk of Alzheimer’s disease years later.
Researchers continue to learn more about how abnormal blood pressure is linked to the risk of developing various forms of dementia, including Alzheimer’s disease. Studies have shown that intensive blood pressure lowering may reduce the risk of mild cognitive impairment, a brain condition that causes memory and thinking problems that often progresses to full-blown Alzheimer’s.
Although the study looked only at older men, the same may be true to older women. Many studies have demonstrated that men and women do not differ significantly in term of their prevalence for “reverse dipping”.
Studies also suggest that men and women who take drugs to keep blood pressure in check may be somewhat protected against Alzheimer’s disease. If you are prescribed blood pressure drugs, it is important to keep taking them to keep blood pressure in check and improve your health overall.
The study authors suggest that a next step would be to examine whether lowering high nighttime blood pressure readings — for example by taking blood pressure medicines in the evening rather than the morning — might have unique benefits for brain health.
By ALZinfo.org, The Alzheimer’s Information Site. Reviewed by Marc Flajolet, Ph.D., Fisher Center for Alzheimer’s Research Foundation at The Rockefeller University.
Xiao Tan et al. “Reverse dipping of systolic blood pressure is associated with increased dementia risk in older men: A longitudinal study over 24 years.”Hypertension, February 8, 2020