Middle-aged people can suffer from high blood pressure without realizing it because their hypertension only occurs at night, scientists have found.
A new study from the University of Oxford found that one in eight people aged 40 to 75 had high blood pressure at night that would never be noticed during a normal daytime screening.
Healthy people usually see a nightly drop in blood pressure. But researchers found that 15 percent of people experience the opposite — experiencing a dangerous surge at night that can lead to heart disease, stroke, and even death.
Current guidelines from the National Institute for Health and Care Excellence recommend that primary care physicians diagnose hypertension based on daytime blood pressure readings alone.
But the team has called for more widespread use of ambulatory blood pressure monitoring, in which a cuff is worn over a 24-hour period to take measurements when people are both awake and asleep.
Lionel Tarassenko, professor of electrical engineering and founding director of the Institute of Biomedical Engineering at the University of Oxford, said: “Daytime blood pressure measurements are not enough.
“Blood pressure follows a cyclical pattern over 24 hours. Normally, it drops at night during sleep and then rises after waking.
“With ‘reverse dippers’ – mostly elderly people, sometimes with diabetes or kidney disease – the pattern is reversed. Blood pressure goes up at night and then drops after waking.
“This means that ‘reverse dippers’ have their lowest blood pressure during the day, and thus are falsely reassured by daytime monitoring at home or in the GP’s office.”
Need for 24-hour monitoring
If undiagnosed and untreated, high blood pressure can cause cardiovascular disease, one of the leading causes of death and disability in Britain.
The new study involved about 21,000 patients from 28 primary care practices and four hospitals in the Oxford area.
The results showed that 49 percent of hospitalized patients had nocturnal hypertension and 11 percent in the community. At least one in three reverse dippers had at least one cardiovascular disease.
Laura Armitage, doctoral researcher from the Nuffield Department of Primary Care Health Sciences at the University of Oxford, said: “Daytime blood pressure readings are unable to detect high blood pressure in these highest-risk patients whose blood pressure rises at night.
“Our research shows that measuring nighttime blood pressure could help identify one in eight adults in England with undiagnosed hypertension. Importantly, it would also lead to a reduction in cardiovascular disease and death.
“This highlights the need for primary care physicians to offer 24-hour blood pressure monitoring to their patients.”
The research is published in the British Journal of General Practice.