Beware of Blood Pressure Changes at Night
If your blood pressure changes a lot overnight -- either rising or falling -- you may have an increased risk of heart disease and stroke, a new study from Japan reports.
When systolic blood pressure (the top number) jumps up by 20 mm/Hg or more during the night, the risk of heart disease and stroke goes up by 18% and the risk of heart failure increases by 25%.
If people consistently had higher blood pressure readings at night, but normal readings during the day, the risk of heart failure more than doubled. The researchers, writing in the journal Circulation, dubbed this a "riser pattern."
On the other hand, for people with a drop in blood pressure of more than 20%, the study team noted a more than twice the risk of stroke. They called this group "extreme dippers."
"Nighttime blood pressure is increasingly being recognized as a predictor of cardiovascular risk," study lead author Dr. Kazuomi Kario said in a journal news release. He's chair of cardiovascular medicine at the Jichi Medical University in Tochigi, Japan.
Dr. Raymond Townsend, an expert volunteer for the American Heart Association, said blood pressure is typically higher in the morning and lower in the afternoon and evening.
Compared to the overall daytime blood pressure pattern, "blood pressure is generally about 10% to 20% lower during sleep. Sleep time offers a relatively pure look at blood pressure. Most factors that influence blood pressure are minimized during sleep," he explained.
But health care professionals usually rely on in-office blood pressure measurements taken during the day to diagnose high blood pressure and to figure out whether or not a blood pressure medication is working or not, the researchers said. These daytime measurements may miss high blood pressure that happens at night. They can also miss big dips in blood pressure.
Dr. John Osborne, director of cardiology at State of the Heart Cardiology in Dallas, said, "When we measure blood pressure in the office, we're mainly getting daytime blood pressure. Seeing what happens at night can give us a much deeper insight."
Osborne said this study "is another signal that we really need to incorporate ambulatory blood pressure monitoring into the evaluation of high blood pressure. If we only see blood pressure during the day, it dramatically reduces our ability to assess overall risk."
Ambulatory blood pressure monitoring allows doctors to see blood pressure levels over a 24-hour period, according to the American Academy of Family Physicians. Patients are fitted with a blood pressure cuff and sent home with a portable monitor that automatically inflates at regular intervals. The machine also records each blood pressure reading it takes in a day.
The current study included more than 6,300 Japanese adults. Their average age was 69. Almost half were men, and more than three-quarters were on blood pressure lowering medications. The average follow-up time was four years.
During the study, volunteers had 20 daytime and seven nighttime ambulatory blood pressure monitor readings.
So should everyone with high blood pressure get their nighttime blood pressure checked, too?
"The best answer right now is maybe. Keep in mind these were people with some existing cardiovascular disease risk factors [already]," Townsend explained. They were also all Japanese, and the findings might not be generalizable to other populations.
And, though it seems to be slowly changing, reimbursement for ambulatory blood pressure monitoring can be tough to get, Townsend said.
But, he added, "The take-home for me is that there is information available about an individual in their nighttime blood pressure patterns."
Both Townsend and Osborne said changing the timing of blood pressure medications might help, but there's not enough data to say for sure if it would. Both said more research is needed.
Want to check your blood pressure at home? Visit Validate BP, a website from the American Medical Association that checks commercially sold blood pressure monitors to make sure they're effective.
SOURCES: John Osborne, M.D., director, cardiology, State of the Heart Cardiology, Dallas; Raymond Townsend, M.D., American Heart Association, volunteer expert, and professor of medicine and director, hypertension program, University of Pennsylvania
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