Unexpectedly high blood pressure? This might be why

man taking bp

Have you ever found your blood pressure unexpectedly through the roof? It can be scary, and it’s something most of us with hypertension will experience at some point. 

While you might have times where you’re shocked at your blood pressure, these numbers might not be reflective of the situation. There are lots of things that can affect blood pressure – some that you can control, and some you can’t.



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1. Periods

2. Clothes under the cuff

3. Sleep apnea

4. Dehydration


1. Your period (if you have one)

While this doesn’t apply to everyone, those who menstruate know that your period can throw you off. You’re doing well, being active and eating healthy – and then the low moods, and food cravings hit you. Periods aren’t fun in plenty of ways, and that includes the impact they have on your blood pressure. 

There are quite a few ways in which periods can impact your blood pressure. If you suffer from PMS (pre-menstrual syndrome) or PMDD (pre-menstrual dysphoric disorder), you also might see an increase in stress around the onset of your period – and it’s no secret that stress increases your blood pressure. In fact, studies have shown that blood pressure is highest at the onset of menstruation


If your periods have become heavier over time, this can be a sign of decreased oestrogen. Decreased oestrogen can constrict your blood vessels, which in turn can increase your blood pressure. If you lose a lot of blood during your period, it can lead to anaemia – which can both increase or decrease your blood pressure.

lady clenching stomach

2. Clothes under the cuff

Taking your blood pressure correctly is a key part of getting an accurate reading. Wearing clothes under your cuff is one of the easiest ways to get an inaccurate reading, but it’s also one of the easiest to fix. A general rule to consider is: the thicker the item of clothing, the higher your reading will be. When taking your blood pressure, wear something that you can take off like a jumper, or something you can roll up like a loose long-sleeve top.

There are several other tips you can use to make sure you’re getting the most accurate reading. When taking your blood pressure, make sure you’re seated comfortably, with both feet flat on the floor. It’s best to also rest the arm you’re taking your blood pressure with flat on a table. Even a full bladder can increase your blood pressure – it’s hard to relax when you need to pee!

3. Sleep apnea

Sleep apnea is a common condition where your breathing stops for a few seconds while you sleep. It’s estimated to affect around 25% of men, and 10% of women. It’s most common in overweight people – but the symptoms are easy to miss. Single people are the least likely to get a diagnosis, as there is no one to notice the tell-tale sign of loud snoring. If you have it, you might also feel extremely tired during the day, and wake up with a headache. It’s estimated to affect between 30 and 50% of people with hypertension, so it’s worth keeping an eye on your sleeping habits. 


If you have mild sleep apnea, you might not need any treatment. People with moderate and severe sleep apnea might need to use a CPAP machine – a type of mask that helps you breathe in your sleep. It’s very important to use the CPAP, as it can reduce the chance of complications from sleep apnea. The regular drops in blood oxygen level cause strain on the heart, and can lead to high blood pressure. If you find out you have sleep apnea, you might find that using a CPAP will help your blood pressure – but speak to your doctor before making any changes to how you manage your blood pressure.

4. Dehydration 

person holding glass of water

It’s quite easy to slip into a chronic state of dehydration – and this can leave you feeling a bit worse for wear. Mild dehydration can make you feel tired, thirsty and cause dry lips and eyes. Severe dehydration can cause confusion, rapid heartbeat and dizziness. While very severe dehydration can be serious, this is rare in the UK unless someone you’re very sick with another illness, have been over-excercising, or misusing diuretics. While you do get an amount of water from your food, it’s important to drink water whenever you’re thirsty as mild dehydration often goes unnoticed. If you have dementia, or are a carer for someone with dementia, it’s important to try and pay particular attention to dehydration – it’s more likely to go unnoticed in these cases

Dehydration can send your blood pressure either way. It can cause a drop in blood volume, which often leads to low blood pressure. However, it can also cause your blood vessels to constrict – which means that your blood pressure increases. Whether it increases or decreases your reading, taking your blood pressure while dehydrated won’t give you a true picture of the situation. 

Is there anything else you’ve noticed that unexpectedly raises blood pressure? Let us know in the comments below

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