Imperial College London

Know Your Numbers! Week: Exploring the silent threat of high blood pressure

by ,

Professor Neil Poulter

Professor of Preventive Cardiovascular Medicine, Neil Poulter, shares how we can adopt a proactive stance against high blood pressure.

This week is Know Your Numbers! Week, the UK’s biggest blood pressure testing and awareness event. Organised by Blood Pressure UK, their primary objective is to decrease the nation’s blood pressure to reduce death and disability from stroke and heart disease.  

In the UK, over half of all strokes and heart attacks are caused by high blood pressure (or hypertension), making it a significant health concern. Nevertheless, almost one-third of UK adults are oblivious to their hypertensive condition. 

To understand cardiovascular wellness better, we sat down with Neil Poulter, Professor of Preventive Cardiovascular Medicine at Imperial’s School of Public Health, to find out how to adopt a proactive stance against the far-reaching consequences of high blood pressure.   

What exactly is blood pressure? 

Prof Neil Poulter (NP): Blood pressure, as the name suggests, is the pressure that blood exerts on the arteries as it is pumped around the circulation by the heart. Arteries are the blood vessels that leave the heart and go around the body, while veins carry blood back to the heart. The heart is a pump made of muscle; when it contracts, it pushes the blood around the body. The pressure of the blood against the vessel wall is what we know as blood pressure.   

Why does blood pressure reading have two values? Is the top or bottom number most important? 

NP: The top value shows the blood's peak pressure, which is called systolic pressure (the top number). Simply put, systolic pressure is the peak pressure reached when the heart muscle contracts. When the heart muscle relaxes, there’s a trough in the pressure. This is called diastolic pressure. So, you've got the systolic and diastolic pressure values which will help you predict the adverse events associated with high blood pressure. If you had to choose between the two values, the top number would be the most important to consider. In older patients, the top value is a better predictor of adverse cardiovascular events. Contrastingly, in younger patients, say under 50 years, the diastolic is the more important figure to consider when diagnosing patients.  

Could you explain the categories of blood pressure readings from hypertensive crisis, and what health risks are associated with each category?  

NP: Usually we consider 140/90mmHg and above as hypertension. If the systolic pressure is above 160, it would be severe. Crises occur at very high levels which are usually associated with severe symptoms.  

What is the danger of having high blood pressure? 

NP: High blood pressure is the biggest single cause of death in the world. Recently, we learned that in a year it kills about 10.7 million people per year globally which is about 30,000 deaths per day, a terrible health burden. High blood pressure is a major cause of heart attacks, stroke, heart failure, kidney failure and dementia. 

What factors can influence blood pressure levels, both temporarily and in the long term? 

NP: Our blood pressure is constantly being elevated due to day-to-day activities. If you’ve got a full bladder, your blood pressure will go up. Whilst I’m talking, my blood pressure is going up. If you’re watching Manchester United (or whatever your favourite football team is) and you get excited, your blood pressure goes up. Your blood pressure as a reaction assists you in running away, fighting or whatever it is your body needs you to do. That’s good – it's supposed to happen! 

However, the causes of high blood pressure, as we understand it, boils down to long term choices made in our lifestyle. The Western diet consists of high levels of alcohol and salt, and not enough fresh fruit and vegetables all of which contribute to high blood pressure. Consuming excess caffeine, such as Red Bull and excess coffee can also contribute to high blood pressure. I spent five years in Africa on the north shores of Lake Victoria, where I found a population who didn’t have a single case of high blood pressure. However, as soon as these people migrated into Nairobi, the city diet and lifestyle resulted in some of these people developing high blood pressure. 

Additionally, as you get older, your blood pressure tends to rise. But that’s probably due to you being exposed to all the bad things in your diet and lifestyle for a longer period of time. In general men, certainly up to the age of about 70, have higher blood pressures than women. Genes do play a role in determining whether we will have high blood pressure. However, the genes on their own almost never give you high blood pressure; they need a conducive environment to interact with the genes.  

Why is it important for individuals to be aware of their blood pressure numbers and to monitor them regularly? How often should they measure blood pressure? 

NP: We call blood pressure the ‘silent killer’ because most patients don’t know they have symptoms, and thus won’t take preventative measures to manage it. You tend to get symptoms only when the illness has been around for a very long time or is severe. By then a lot of damage has been done to your arteries and also potentially to your brain, kidneys and heart.  

In general, young women tend to get their blood pressure measured more frequently than young men. This is due to factors such as the contraceptive pill and pregnancy when blood pressure is routinely measured. So, women have more measurements made earlier on in life compared to men. 

The frequency at which you monitor your blood pressure will depend on how old you are and how high your blood pressure is. If you're young, say in your twenties and you're not pregnant, you can check it every three to four years, something like that. But once you get into your thirties you should be doing it probably every year. If your blood pressure is high, you need to get it measured frequently until it is controlled. For people on medication, for example, it should be measured every six months. 

Are there specific populations that are more prone to developing high blood pressure, and if so, why? 

NP: Within the UK, the African-Caribbean population tend to have higher blood pressure, as do people from South Asian backgrounds, compared with those of White European heritage. You can also find some of the world’s highest rates of hypertension in Black African people. Some cuisines—like that in the Philippines—tend to consist of a lot of salt – ingredients such as soy sauce and fish sauce are all incredibly salty - and consequently their blood pressure levels tend to be high. In the last decade or two, the Portuguese have had a big population drive to cut down salt in their diet because they suffered from high stroke rates and very high blood pressure levels. Ultimately, it often boils down to the cuisines of the different ethnic groups.  

How can individuals manage their blood pressure? 

NP: You need to start by changing your diet and lifestyle, for example by increasing the amount of exercise and cutting down on salt and calories. People often think salt only comes from the saltshaker, but that's only about 10% of your salt intake. The most common source of salt in the British diet is bread and most breakfast cereals – such as cornflakes, a bowl of which has got the same salinity as seawater. So, I get my patients to cut down on their salt intake by not eating bread and breakfast cereals and encouraging them to eat more fresh fruit and vegetables. 

What are some potential barriers or challenges that might prevent people from prioritizing regular blood pressure screenings in the UK? 

NP: The main barrier that prevents people from prioritising regular blood pressure screenings in the UK is the fact that because people feel fine, they assume they are not suffering from hypertension, which may not be the truth. Whether you’re experiencing symptoms or not it is important to get your blood pressure checked because it is a ‘silent killer.’


Mengmeng Tu

Mengmeng Tu
Centre for Languages, Culture and Communication

Ruth Ntumba

Ruth Ntumba
Faculty of Medicine Centre