Middle-aged people may suffer from high blood pressure without realizing it because their hypertension only happens at night, researchers have found.
A new study from Oxford University found that one in eight people aged 40 to 75 had high blood pressure at night that would never be picked up during normal daytime screening.
Healthy people usually see a nocturnal drop in blood pressure. But researchers found that 15 percent of people experience the opposite – suffering from 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 GPs diagnose hypertension based only on daytime blood pressure readings.
But the team has called for more widespread use of ambulatory blood pressure monitoring, where a cuff is worn over a 24-hour period to take readings when people are both awake and asleep.
Lionel Tarassenko, professor of electrical engineering and founder of the Institute of Biomedical Engineering at Oxford University, said: “Daytime blood pressure readings are not enough.
“Blood pressure follows a cyclical pattern over 24 hours. Normally it drops at night during sleep and then rises after waking up.
“For ‘reverse dippers’ – mostly older people, sometimes with diabetes or kidney disease – the pattern is reversed. Blood pressure rises at night, then falls after waking up.
“This means that ‘reverse dippers’ have their lowest blood pressure during the day, and so they will be falsely reassured by daytime monitoring at home or in the GP clinic.”
Need for 24-hour monitoring
When undiagnosed and untreated, high blood pressure can cause cardiovascular disease, which is one of the leading causes of death and disability in the UK.
The new study involved around 21,000 patients from 28 GP practices and four hospitals in the Oxford area.
The results showed that 49 per cent of hospital patients had nocturnal hypertension and 11 per cent in the community. At least one in three reverse dippers had at least one cardiovascular disease.
Laura Armitage, PhD Fellow at the University of Oxford’s Nuffield Department of Primary Care Health Sciences, said: “Daytime blood pressure measurements are unable to detect high blood pressure in these patients at highest risk if blood pressure rises at night.
“Our research shows that measuring blood pressure at night can help identify one in eight adults in England who have undiagnosed hypertension. Importantly, this will also lead to a reduction in cardiovascular disease and death.
“This underlines the need for GPs to offer 24-hour blood pressure assessment to their patients.”
The research was published in the British Journal of General Practice.