Middle-aged people may be suffering from high blood pressure without realising it, because their hypertension only happens at night, scientists have found.
A new study by Oxford University found that one in eight people aged 40 to 75 had night-time high blood pressure that would never be picked up during normal daytime screening.
Healthy people usually see a nocturnal dip in blood pressure. But researchers found that 15 per cent of people experience the opposite - suffering a dangerous rise at night that could 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 on daytime blood pressure measurements only.
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 Oxford University, said: “Daytime blood pressure measurements are not enough.
“Blood pressure follows a cyclical pattern over 24 hours. Normally, it goes down at night during sleep and then rises after waking.
“For ‘reverse dippers’ - mostly elderly people, sometimes with diabetes or kidney disease - the pattern is reversed. The blood pressure goes up at night, and then decreases after waking.
“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 main causes of death and disability in Britain.
The new study involved about 21,000 patients from 28 GP practices and four hospitals in the Oxford area.
The results showed that 49 per cent of the hospital patients had night-time hypertension and 11 per cent in the community. At least one in three reverse dippers had at least one cardiovascular disease.
Laura Armitage, doctoral research fellow of the University of Oxford’s Nuffield Department of Primary Care Health Sciences, said: “Daytime blood pressure measurements are not capable of detecting high blood pressure in these highest-risk patients whose blood pressure rises at night.
“Our research shows that measuring night-time blood pressure could help identify the one in eight adults in England who have undiagnosed hypertension. Importantly, this would also lead to a reduction in cardiovascular disease and death.
“This highlights 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.