What causes high blood pressure?

Written by Dr Katie Stephens, GP

Dr Katie graduated from the University of Manchester in 2007 (MBChB) and completed her GP training in the West Midlands in 2012 (MRCGP). 

 

What is high blood pressure?

Do you know what the phrase ‘blood pressure’ means? When blood flows through our blood vessels, it pushes against the blood vessel walls. We can measure how hard it is pushing against the walls with a machine. The level of pushing is what we mean by ‘blood pressure’.

When this pressure is higher than what is healthy for us, we call it ‘high blood pressure’. The medical diagnosis is hypertension. High blood pressure matters because it commonly causes serious problems such as strokes and heart attacks. These problems can be prevented by lowering blood pressure through lifestyle changes and taking medication. If you would like to know if your blood pressure is high, please use our Blood Pressure Tool.

What causes high blood pressure in general?

There are many things that can increase your risk of having high blood pressure, including:

• Being overweight
• Smoking
• A lack of exercise
• Dietary causes (e.g., lots of salt, excess caffeine and alcohol)
• High blood pressure in the family
• Being of South Asian or Black ethnicity
• Stress
• Having high cholesterol levels
• Being over the age of 65y
• Certain medical condition (e.g., Diabetes, Kidney Disease, Obstructive Sleep Apnoea)
• Certain medications (steroids, anti-inflammatory medications, the combined contraceptive pill)

What causes high blood pressure in young adults?

It is much less common for young adults to suffer from high blood pressure. If they do, we usually want to check for underlying causes, such as problems with the adrenal glands. The adrenal glands sit above each kidney and make a number of hormones which affect the blood pressure. If they aren’t working properly, this can lead to high blood pressure.

Other possible causes of high blood pressure in young people include problems with the kidneys, blood vessels, or thyroid gland, as well as taking certain medications. Sometimes it can also be caused genetically. If you have high blood pressure and are under the age of 40, speak to your doctor about whether or not you need any extra tests.

What is the link between these risks and high blood pressure?

Let’s look in a bit more detail at the relationship between some of the above risk factors and high blood pressure.

Stress and high blood pressure

There appear to be links between both short-term and long-term stress and high blood pressure. One review paper published in Neurological Research found that long-term stress seems to roughly double the odds of getting high blood pressure. It also found that there was more stress among the people with high blood pressure than those with normal blood pressure. There were limitations to the study and more research needs to be done for us to really understand how stress impacts the risk of getting high blood pressure, but this is certainly worth taking seriously.

Foods to avoid with high blood pressure

What we eat and drink can have a big impact on our blood pressure:

• Salt raises blood pressure. Pregnant women should avoid having too much as well as too little salt in the diet. For everyone else who has high blood pressure, cutting down on your salt is very likely to reduce your blood pressure. Depending on what your usual diet is like, you might notice a difference even within a few hours. For most people, it is recommended to limit your sodium intake to 2,300 mg/day. For maximum benefit, unless advised otherwise by your doctor, aim to have no more than 1,500 mg/day.
• Caffeine can raise blood pressure within an hour of drinking it, and may keep it raised for around 3 hours. It may also do much more: a 20 year study published just a few months ago showed that, for people with very high blood pressure (160/100 mmHg or higher), drinking ≥2 cups of coffee daily appeared to double their risk of dying from cardiovascular disease (e.g. having a stroke or heart attack).
• Alcohol can raise blood pressure – more on this below.
• Fatty foods can raise cholesterol levels. When cholesterol builds up on the inner walls of our arteries, this can cause high blood pressure, as well as other health problems too.

Healthy eating choices should involve choosing foods from the main food groups (whole grains, vegetables, fruits, meat/poultry/fish cooked in healthy ways) and limiting foods that aren’t good for us, like sweets, sugary drinks, fatty meats, and foods high in salt. Healthy eating should avoid ultra-restrictive diets that only focus on a couple of ‘superfoods’ and are hard to stick to. A great plan to follow is the DASH (Dietary Approaches to Stop Hypertension) diet, which includes major food groups and helpful portion suggestions.

Is exercise good for high blood pressure?

Getting enough exercise can both prevent high blood pressure from ever occurring, and lower the blood pressure in people who already have hypertension. One study showed that exercising reduced both the top and bottom blood pressure numbers for people with hypertension by about 5 – 7 mmHg. There are a few thoughts as to how exercise lowers blood pressure:

1. Exercise appears to help blood vessels relax. When they relax, they get bigger. This means there is more space for blood to flow through them, and less pressure from the blood on the blood vessel walls. Imagine changing from a tight pair of jeans into something with an elastic waistband – the pressure you feel on your tummy (and the pressure your tummy puts on your waistband) reduces when it can take up more space. Exercise is like letting our blood vessels change from being tight jeans into comfy, elasticated jogging bottoms – the blood pressure drops when our blood vessels relax and the blood has more space.
2. Exercise makes the heart muscles physically stronger. This means the heart can pump blood around the body without having to squeeze quite as hard, i.e. the blood pressure is lower.
3. In people who have heart damage as a result of high blood pressure (left ventricular hypertrophy), exercise appears to help repair the damage and may reform the heart muscles into a healthier shape. This change appears to happen alongside a reduction in blood pressure. A possible explanation here is that the healthier heart shape is able to pump more efficiently, leading to a lowered blood pressure.
4. Exercise can also help people shed excess fat. Excess fat can cause high blood pressure through squeezing the kidneys. This then causes changes in the body which raise the blood pressure to force blood through the kidneys. Taking away the excess fat can reverse some of these changes, leading to a lowered blood pressure.

If your blood pressure is very high (i.e. top number between 170 – 180, or bottom number between 100 – 110), it would probably be best to speak to your doctor or nurse before starting an intensive new exercise regime. If your blood pressure is between 160-170 on the top and 90 – 100 on the bottom, and you haven’t exercised much recently, it may be wise to begin with lower intensity exercise, such as going for a gentle walk, and see how you manage, before increasing the exercise intensity.

If your blood pressure is extremely high (above 180 on the top or 120 on the bottom), it’s important that you get urgent medical attention in person as soon as possible. You can access this by contacting your NHS GP in hours, or ringing 111 for out of hours support. If you also feel unwell (e.g, if you have chest pain, ankle swelling, shortness of breath, visual changes or feel confused), please have someone take you to A&E immediately.

Can lack of sleep cause high blood pressure?

It can, indeed! Blood pressure changes throughout the day and night as our heart responds in real time to what our bodies need. When we sleep, our bodies don’t need as much oxygen and energy, and our blood pressure dips down lower. Sleeping less means this dip is shorter, and blood pressure averages in a 24 hour period will be higher. This can affect lots of people, such as:

• People who habitually sleep less, including those who work night shifts
• People with sleep disorders, e.g., insomnia
• People with conditions that affect sleep quality indirectly, e.g., restless legs syndrome.
• People with medical conditions directly linked to poor quality sleep, such as Obstructive Sleep Apnoea (OSA).

There are strong links between having OSA and high blood pressure. Fortunately, treating OSA through using a ‘Continuous Positive Airway Pressure’ breathing machine, or CPAP machine, has been shown to help lower blood pressure. The effects appear to be greater for people with more severe OSA symptoms, higher starting blood pressures and those who are able to keep on using the CPAP machines as directed.

On top of this, people who are tired from not sleeping enough (for whichever reason) may make other lifestyle choices that can contribute to a higher blood pressure, such as exercising less or eating less healthy foods.

Alcohol and high blood pressure

Alcohol can raise blood pressure in both the short and the long term. While having a single glass of alcohol is unlikely to affect blood pressure very much, having a few drinks in one sitting can make your blood pressure go up temporarily a few hours later. If this happens often enough, it can cause changes in your body (such as changes to hormone levels) that can lead to a blood pressure that goes up and stays up.

The UK government advises keeping your alcohol intake to less than 14 units per week, and avoiding binge drinking (i.e. no more than 2 standard drinks in an evening). If you drink most days, it may not be safe to suddenly stop drinking, although usually cutting back by about half is both safe and helpful. Blood Pressure UK has further links for support and information about alcohol and high blood pressure.

Can Covid-19 cause high blood pressure?

While this is still being studied, there are published reports suggesting that Covid-19 does appear to increase the risk of having high blood pressure. One study of 153 people who were admitted to hospital in Turkey with Covid-19 found that, in general, most people’s blood pressure went up a little in the month after having Covid. For 18 people in the study group, the increase in their blood pressure was high enough that they were considered medically to have hypertension for the first time.

Another study looked at how blood vessels and blood pressure respond 2-3 months down the line after a mild Covid-19 infection in mainly healthy young adults. It suggests that blood vessels become more stiff (think back to that jeans vs elastic waistband analogy from earlier) and blood pressure increases after Covid-19 infection, and also that these changes seem to get worse with time. While this is of course concerning, more research needs to be done in order to understand the link between Covid-19 and high blood pressure more fully. If you have had Covid recently and don’t know what your blood pressure is, please get it checked.

Can menopause cause high blood pressure?

Absolutely. Not only does the risk of having high blood pressure increase generally as both men and women get older, but there are also several ways that less oestrogen in menopause may lead to a rise in blood pressure:

• Increase in weight
• Increase in sensitivity to salt
• Making blood vessels constrict (the opposite of relaxing)
• Fluid retention

On top of this, some classical menopausal symptoms such as hot flushes and palpitations may potentially be caused not by hormone changes, but by a high blood pressure. If you think you may be peri-menopausal, please do make sure you know what your blood pressure numbers are.

Can diabetes cause high blood pressure?

Diabetes doubles the risk of having high blood pressure. In fact, most adults who have diabetes also have hypertension. The relationship goes the other way also – people with hypertension have a greater chance of also getting diabetes.

It seems that diabetes can cause high blood pressure through its effects on different parts of the body:

• Making blood vessels less elastic and more stiff
• Causing salt retention leading to fluid retention
• Causing kidney damage (leading to various changes that increase blood pressure)
• Damaging the nervous system, which leads to the heart beating harder

To summarise, there are a number of possible causes of high blood pressure, ranging from the more well-known (being overweight, lack of exercise) to some which may be lesser known (after a Covid infection, not sleeping enough). Regardless of the cause, high blood pressure is dangerous. It can lead to strokes and heart attacks, and most of the time doesn’t cause any symptoms. If you think you might have one of the risks factors mentioned in this article, or even if you’ve just not had your blood pressure measured recently, please do go out and get it checked. You can do this for free at many gyms and pharmacies, or you could pick up an inexpensive machine from Kinetik Wellbeing or elsewhere (please just make sure if you buy it from somewhere else, that it is on the BIHS’ list of approved blood pressure monitors). Once you have a reading, pop it in our blood pressure tool to see where you stand.