What is diastolic blood pressure?

At Hilo we live and breathe blood pressure. You could even say it’s in our blood. But while we’re confident discussing what the numbers mean, our recent research in both the UK and Germany has shown us that many people aren’t. This short article will outline what ‘diastolic blood pressure’ is, why it’s important, and what you can do to make sure your numbers stay within healthy limits. 

Blood pressure 101: what the numbers mean

Your blood pressure is an important health metric, so much so that it’s likely to be one of the first things your physician measures. But it’s also an aspect of our health we’re inclined to overlook, because it’s ‘just there’. And that’s the issue. If your blood pressure is high or low it’s usually symptomless, so you may not know that your heart is working too hard – which could have a severe impact on your overall health. 

With a blood pressure (BP) reading there are two numbers: one larger (the top one), and one smaller (the bottom one). These numbers mean different things and can reveal to a medical professional whether your blood pressure is too high, too low, or just right – in the Goldilocks zone. 

• The larger, or top, number is your systolic blood pressure, and is the highest pressure exerted by the heart onto your arteries during a single beat.

• The smaller, or bottom, number is your diastolic blood pressure, and is the residual pressure in your arteries between heart beats.

When looking at blood pressure measurements, the larger number, the systolic blood pressure, usually receives more attention. This is because hypertension, or cardiovascular conditions, are often hallmarked by a high systolic BP but normal diastolic BP. However, it’s just as important to keep an eye on this small – and sometimes neglected – number as well, especially if it is creeping towards, or exceeding, 90 mmHg.

Diastolic blood pressure and IDH

While diastolic blood pressure is often ignored, it can be a good predictor for the likelihood of developing high blood pressure (hypertension) or other cardiovascular disorders. It is also linked to a specific type of hypertension, which is not widely discussed: isolated diastolic hypertension (IDH).

In this condition, systolic blood pressure is below the hypertensive range limit, but diastolic blood pressure is above. And, in-line with other types of hypertension, IDH can lead to an increased risk of serious medical complications including stroke, heart disease, heart attack, and kidney disease.

Being diagnosed with isolated diastolic hypertension (IDH) depends, in part, on where you live. In the UK and EU, guidelines from the European Society of Cardiology (ESC)/National Institute for Health and Care Excellence (NICE) are followed, meaning that your diastolic BP measurement needs to be over 90 mmHg, but your systolic will be <140 mmHg.

In the United States it’s slightly different. In 2017, the American College of Cardiology(ACC)/American Heart Association Task Force (AHA) redefined their High BP Guideline: the threshold for overall hypertension was lowered to 130/80 mmHg. This, in turn, means that IDH is defined as having a diastolic BP ≥80 mmHg with a systolic BP <130 mmHg.

You should always follow the advice of your clinician and local healthcare authorities, even if they differ across jurisdictions.

In the UK, through analysis of Biobank data, around 6% of adults have IDH when using the ESC/NICE guidelines (so diastolic BP over 90 mmHg). However, the percentage jumps to 24.5% when using the ACC/AHA guideline (diastolic BP over 80 mmHg). 

Furthermore, individuals with IDH (using either definition) were more likely to be under 55, male, overweight with higher baseline systolic BP and less favourable lipid values. They also had a lower estimated glomerular filtration rate, meaning their kidneys didn’t filter blood as well as they should. Interestingly, social factors seemed to play a role by both standards: people who had a higher Townsend deprivation index were more affected by IDH, while participants with education above A-levels were less susceptible to have developed it. However, it was only when using the ESC/NICE definition of IDH (diastolic BP over 90 mmHg) that subjects were more likely to be diabetic or smokers (current or past). 

What does having IDH mean?

Having IDH can put you at increased risk of cardiovascular diseases, such as heart attack and stroke. This is because any kind of high blood pressure puts strain on the heart as it needs to work harder to maintain proper blood flow which, over time, can cause damage. 

Another risk is possible damage to other important organs, such as the kidneys, eyes and brain. Kidney damage occurs because the higher blood pressure interferes with their delicate, smaller blood vessels, leading to kidney failure or other kidney problems. A similar issue is seen in the eyes: high BP damages the blood vessels, with potential complications ranging from vision problems all the way to blindness. And when it comes to the brain, studies have suggested that there may be a link between high blood pressure and developing dementia, again due to the damage caused to blood vessels.

But hypertension isn’t for older individuals only. Blood pressure levels in mid-life can impact upon your late-life. Research from Imperial College London has shown that having high blood pressure at age 55 or younger increases the risk of coronary heart disease independent of high blood pressure after 55 years of age: in short, if you had hypertension in mid-life but had it under control in your 60s, the damage has already been done. Related to this, long-term research studies have demonstrated that people who had hypertension between 40 and 64 years of age were more likely to develop dementia in later life, particularly vascular dementia (although it should be noted that other factors such as genetics, lifestyle, and overall health can also influence risk). 

The take-home? Controlling blood pressure is an excellent way to ensure heart health in later years, and reduces risk of developing serious health conditions when you get older. So it’s never too young to start!

How can I lower my diastolic BP?

While in normotensive individuals diastolic BP is known to increase until around age 55, then decrease again, it’s still important to ensure that it doesn’t reach unsafe levels. The way to reduce diastolic BP are effectively the same as for reducing overall BP:

• Exercise regularly
• Eat healthily
• Cut down on salt
• Moderate alcohol consumption
• Avoid smoking
• Reduce stress

However, it should be noted that a low diastolic BP can also be a bad thing (usually defined as below 60 mmHg), and may indicate inadequate blood flow to the heart. If you’re worried, always talk with a healthcare professional. 

The Hilo Band: a useful weapon for monitoring diastolic BP

The Hilo Band provides continuous, medical-grade monitoring that delivers personalised insights and ongoing guidance, empowering you to take control of your heart health. Blood pressure data are automatically collected night and day, 365 days a year, enabling patterns of long-term cardiovascular health to be revealed; potentially uncovering conditions previously considered difficult to diagnose, such as nocturnal hypertension. And that’s not all! Sleep data and step-count are also measured, allowing direct correlation between lifestyle interventions and blood pressure behaviours. 

The information in this article is intended for educational purposes only and does not contain nor replace medical advice. If you suspect hypertension or are worried about your blood pressure, speak to your doctor. They can advise on the best way to effectively manage it.

FAQ

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