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Around 15% of people aged 40-75 may have a form of undiagnosed high blood pressure (hypertension) that occurs only at night-time. Because they do not know about this, and therefore are not being treated for it, they are at a higher risk of cardiovascular disease such as stroke, heart failure, and even death, suggests new research from the University of Oxford published in the British Journal of General Practice.

Woman holding her hands to her chest

When blood pressure is monitored over 24 hours, individuals can be divided into three groups according to their blood pressure pattern:

  • ‘dippers’, for whom the night-time blood pressure is lower than the day-time blood pressure (which is the case for healthy young people),
  • ‘non-dippers’, for whom night-time and day-time blood pressure values are not very different, and
  • ‘reverse dippers’, for whom, contrary to expectations, the night-time blood pressure is higher than the day-time blood pressure, when they are up and active.

When undiagnosed and untreated, hypertension (also known as high blood pressure) causes cardiovascular disease, which is one of the main causes of death and disability in the UK. 1 in 8 people in England have undiagnosed hypertension, putting them at risk of cardiovascular disease.

24-hour blood-pressure monitoring (usually called ambulatory blood pressure monitoring, ABPM) has become less frequent in primary care since the beginning of the COVID-19 pandemic. Home blood-pressure monitoring, using a monitor often purchased by individuals themselves, is the common alternative. However, home blood-pressure monitors cannot be used when the individual is asleep and so cannot measure night-time blood pressure. Therefore, those people whose blood pressure is normal during the day but whose night-time blood pressure, unbeknown to them, rises at night have undiagnosed hypertension, with all the associated risks.

This new study from the University of Oxford looked at 24-hour blood pressure patterns in patients admitted to hospital, and found that nearly half of these patients have a blood pressure rise at night (‘reverse-dipper pattern). The study researchers then looked at blood pressure patterns from patients in primary care from the same age group (40-75), who had been monitored for 24 hours during their normal daily activities using ABPM. The proportion of the population in this group who were ‘reverse-dippers’ was around 15%. There are several possible reasons for the difference in the proportion of people found to have a ‘reverse dipping’ blood pressure pattern in the two patient groups. One possible reason is that the community group included a much higher proportion of people who had already been diagnosed with hypertension, and these people are more likely to be ‘dippers’ rather than ‘reverse dippers’. This is because people whose blood pressure is highest in the day and drops at night are more likely to get picked up as having hypertension in GP surgeries and clinics.

Read the full story on the University of Oxford website

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