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(CNN) —  

When a patient’s blood pressure reads normal at home and high in a doctor’s office, it’s called “white coat hypertension” – and new research suggests that it is not a benign condition.

Patients with this condition who do not take hypertension medication are twice as likely to die of heart disease than normal-pressure patients, a meta-analysis published Monday in the journal Annals of Internal Medicine finds.

Exercise, eat right and avoid alcohol and cigarettes

Blood pressure is a measure of the force at which blood flows through our veins, arteries and capillaries, and when that force is too great, it is called hypertension or high blood pressure. In numbers, high blood pressure is considered anything above 130/90. The first number, the systolic pressure, reflects the pressure in vessels when the heart beats. The second number, diastolic, measures when the heart is at rest.

Doctors do not know what causes white coat hypertension, which may have different triggers in different patients. For some people, anxiety may cause their blood pressure to rise in a medical setting, but others may have fluctuating blood pressure due to an underlying physiological condition.

About 1 in 5 American adults may have white coat hypertension, research suggests. To understand the health risks, Penn Medicine researchers reviewed 27 studies involving more than 64,000 patients in the United States, Europe and Asia. Compared with people with normal blood pressure readings both at home and in the office, patients with white coat hypertension were at elevated risk for cardiovascular events and death.

Patients with untreated white coat hypertension had a 36% increased risk of heart disease, 33% increased risk of death due to any cause and 109% increased risk of death from heart disease, the analysis found.

This finding was “most robust” in studies where participants were 55 years old or older on average and studies that included patients with previous cardiovascular disease, according to Dr. Jordana Cohen, co-author of the study and an assistant professor of medicine and epidemiology at University of Pennsylvania Perelman School of Medicine.

One separate group of patients with variable blood pressure readings did not face elevated risk – those experiencing the white coat “effect.” These are patients whose blood pressure only reads high in the doctor’s offices, but normal at home, and are already taking blood pressure medication. They experienced no increased risk of cardiovascular events or mortality, the analysis showed.

Although more research is needed, “we encourage lifestyle modifications (including improved diet, exercise, weight loss, reduction in alcohol use, and smoking cessation) in all patients found to have white coat hypertension,” the researchers concluded.

A ‘comprehensive’ and current analysis

Dr. Daichi Shimbo, a cardiologist and an associate professor of medicine at Columbia University Medical Center, said the new meta-analysis is “really important” because the researchers’ examination of published studies both was “really comprehensive” and included recent research. Shimbo, who was not involved in the study but who co-authored an editorial published alongside the meta-analysis in the Annals of Internal Medicine, explained that “for a long time, it’s been thought that white coat hypertension is benign and not associated with increased risk.”

The new research suggests otherwise, Shimbo said, though he noted that the finding “doesn’t apply to everyone.”

“If you were older – you were at least 55 years of age – or you had a history of cardiovascular disease or you had chronic kidney disease or diabetes, white coat hypertension was associated with an increased risk of cardiovascular events and mortality,” he said.

Additionally, the elevated risk in white coat hypertension patients is “not strong; it’s not weak; it’s somewhere in the middle,” said Shimbo, who wondered about the risks for people not included in the analysis: those with sustained hypertension (high readings both inside and outside the doctor’s office).

Pulling data from the papers examined in the meta-analysis, Shimbo and his co-author, Paul Muntner, associate dean of research at the University of Alabama at Birmingham School of Public Health, found that sustained hypertension patients “have a really substantially increased risk for cardiovascular events and mortality” compared with people with normal blood pressure, he said: “It makes sense, right?”

The risk of cardiovascular events and death among white coat hypertension patients is somewhere in the middle of the spectrum and is “substantially lower” than that of patients with consistent high blood pressure readings, he said.

Despite finding elevated risk for cardiovascular events, including heart attacks and coronary artery disease, the meta-analysis found no relationship between white coat hyertension and stroke. “This unexpected finding may benefit from further investigation,” Shimbo and Muntner noted.

Recent guidelines in both the United States and Europe recommend blood pressure monitoring to screen for white coat hypertension and white coat effect, Shimbo said, and he too emphasized “the importance of doing out-of-office monitoring to diagnose hypertension.”

Most guidelines say that ambulatory monitoring – in which a patient wears a sophisticated device that automatically inflates and deflates, measuring blood pressure even during sleep – is the preferred approach, yet it is not available to everyone, he explained.

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Home monitoring – in which a patient self-measures blood pressure, usually with a store-bought device that is not fully automatic – is more practical and worthwhile, Shimbo said, adding that patients need to get a “decent device that is accurate” and to make sure they follow instructions.

The American Heart Association recommends an automatic, cuff-style, bicep (upper-arm) monitor that has been validated – ask your pharmacist for advice – and offers tips on how to use it correctly.