Daytime, Nighttime Blood Pressure Both Important

(HealthDay News) -- A major study challenges the idea that high nighttime blood pressure readings are better indicators of health risk than measurements taken in the daytime.

"Our findings support recording the ambulatory blood pressure during the whole day," meaning 24 hours, concluded the report in the Oct. 6 issue of The Lancet.

The study, led by physicians at the University of Leuven in Belgium, followed almost 7,500 participants on three continents for an average of nearly 10 years.

It found that persons with higher nighttime than daytime readings did have a higher death rate, but that was because they tended to be older and sicker.

"Some people have said that blood pressure at night is the best predictor of risk," said Dr. Thomas G. Pickering, director of the Center for Cardiovascular and Behavioral Health at Columbia University. "This study says that is not actually the case, that pressure over the whole 24-hour period is [best]," said Pickering, who was not involved in the research.

Pickering chaired an American Heart Association committee that in 2005 recommended that physicians and patients move toward 24-hour blood pressure monitoring.

"We are going to make new recommendations about home blood pressure monitoring to say that it should be used much more widely than it is at the moment," he said.

High blood pressure, defined as two consecutive readings over 140/90, increases the risk of heart disease, stroke and kidney disease. An estimated 50 million Americans have high blood pressure. Many take medications for the condition and follow current guidelines for monitoring.

According to the new study, previous reports linking higher nighttime blood pressure readings with adverse outcomes needed confirmation due to major gaps in their findings. The new trial was designed to close those gaps, the researchers said.

In his accompanying editorial, Dr. Stephane Laurent, of the Universite Paris -Decartes, Paris, contends that the new findings should "significantly affect the next guidelines for ambulatory blood pressure measurement."

Changes already have begun, Pickering said.

"One of the trends is less reliance on blood pressure monitoring in the doctor's office," he said. That trend is being held back, because many health insurance plans do not reimburse for out-of-office monitoring, and because the do-it-yourself technology is lagging somewhat, he said.

Newer home monitors are coming along, Pickering said. "What is going to happen in the future is the availability of monitors that will allow you to take your blood pressure readings at night," he said.

The recommendations that the heart association committee is about to make will principally cover daytime home blood pressure monitoring, Pickering said. "Reading blood pressure at night is a bit in the future," he said.

The new report is valuable, because it puts the issue in perspective, said Dr. George Bakris, director of the hypertensive disorders unit at the University of Chicago.

"There has been tremendous focus on early a.m. readings as giving the highest risk for stroke and so on, so the conclusion some people have made is that the rest of the day is not important," Bakris said. "The beauty of this thing is that it shows that nighttime pressure tells us about certain things, while daytime pressure tells us about other things. It's clear that the night/day ratio is important."

More information
There's more on high blood pressure at the U.S. National Library of Medicine.