Blood pressure fluctuations: What can cause them and what do they mean?

While we often think of blood pressure (BP) as a single number, likely because during a medical check-up only one data point is collected, it’s actually continually changing. These variations throughout the day and night are in-line with your circadian rhythm, or ‘internal body clock’. 

In a healthy individual, BP will start to rise a few hours before waking, continuing upward until around midday, which is when it’s at its highest. It then tends to fall during the late afternoon into the evening, and should be at its lowest overnight – between 10 and 20% lower than your daytime average. If your BP doesn’t reduce during the night, you could be a ‘non-dipper’, a profile sometimes associated with organ damage, as well as poorer renal and cardiovascular outcomes. Another related medical condition is ‘nocturnal hypertension’, where blood pressure is elevated overnight and, defined by the European diagnostic thresholds for nocturnal hypertension as being at or over 120/70 mmHg. This is lower than a daytime value for hypertension of 140/90 mmHg because BP should dip overnight. 

However, while it’s been noted that daily fluctuations in BP are normal, there are several instances where BP can change by a larger degree than may be expected. We’ll list and explain them below.

If you are concerned about your blood pressure, always speak with a medical professional. 

10 times your BP may fluctuate outside your natural rhythm

1. White coat syndrome

White coat syndrome is a condition where your blood pressure is raised due to the stress of being in a medical setting, pushing your measurement higher than it would be if you took it at home. This is not to be confused with white coat hypertension, where your blood pressure readings are over 140/90 mmHg in the clinic – a measurement classified as hypertensive – but lower than 140/90mmHg at home. Both white coat syndrome and white coat hypertension are well-known medical conditions, affecting between 15 and 30% of those with elevated BP at the doctor’s. 

2. Masked hypertension

Masked hypertension is often described as the opposite of white coat syndrome or hypertension, with measurements in the clinic giving values lower than those at home. Studies have suggested that elderly, male, patients with large BP variability are most likely to suffer from masked hypertension. In other patient populations, those with mental stress at home or work may have hypertensive BP outside the clinic, but normal numbers once away from the stressor. Other profiles with a higher risk are smokers or heavy drinkers, as well as those who are sedentary and obese. 

3. Temperature

The weather can have an impact upon blood pressure. On average, your BP is likely to be lower in the summer than it is in winter. This difference is due to something called ‘vasodilation’. Higher temperatures cause blood vessels at your skin’s surface, called capillaries, to dilate so that blood flow can be diverted to these vessels to help dissipate excess heat into the surrounding environment. This means it’s easier to pump blood around the body as there is less resistance, thus reducing blood pressure.

Cold weather causes the opposite. Vasoconstriction is a protective biological feature designed to ensure that your body doesn’t lose too much heat by keeping blood close to your central organs instead of the skin surface. However, constricted blood vessels can result in higher blood pressure as your heart meets more resistance when pumping your blood. 

4. Exercise

It’s normal for blood pressure to temporarily rise during physical exertion. Systolic BP tends to exhibit a linear increase, corresponding to the increased metabolic demands of the body and higher cardiac output (reflected in the rising heart rate), whereas diastolic BP tends to stay more stable. However, working out regularly leads to lower blood pressure overall, which is beneficial to your health. In addition to lowering BP, regular exercise also reduces risk of heart disease, diabetes, obesity, kidney failure and osteoporosis, as well as improving mental clarity and lifting your mood. 

5. A full bladder

Having a full bladder can temporarily increase your BP. In fact, it can cause your systolic BP (the larger number) to go up by 10 to 15 mmHg! This means that it’s important to measure BP when you don’t need to pee!

6. Stress

It’s well known that stress can have a significant impact upon your health. However, not all forms of stress are created equal. Acute (short-term) stress, lasting from minutes to hours, can prove useful – for example keeping your body awake and alert, allowing you to focus for longer. But both episodic acute (where acute stress is experienced on a regular basis) and chronic, or long-term, stress can have a detrimental impact on your overall well-being. 

7. Over-the-counter cold remedies

Over-the-counter (OTC) cold remedies contain decongestants such as pseudoephedrine, ephedrine, phenylephrine, naphazoline, and oxymetazoline. These can contribute to temporary increases in blood pressure, which may be dangerous for people with hypertension. This is because they narrow blood vessels, making it harder for blood to flow through them, resulting in increased resistance and therefore increased BP. 

8. Caffeine

The relationship between coffee and blood pressure is complex. While caffeine can cause a temporary spike in blood pressure, the increase may be short-lived. 

9. Smoking

Smoking raises blood pressure through several mechanisms. The nicotine increases your heart rate and causes arteries to vasoconstrict. Toxins inside cigarette smoke damage blood vessels and smoking may lead to atherosclerosis, the process whereby fat is laid down in your arteries’ walls. In conjunction with this, smoking also increases the likelihood of clot formation. This raises your overall risk of cardiovascular disease.

10. Menstrual cycle

There’s a connection between your menstrual cycle and blood pressure, as well as connections between BP and menstrual symptoms such as heavy bleeding, irregular periods, and PMS. Furthermore, the use of oestrogen-based contraceptives can cause a rise in blood pressure over time in a few cases. For more details, head to our article ‘How does your menstrual cycle influence your blood pressure?’. 

The Hilo Band: easy insight into your BP behaviour

The Hilo Band has been specifically designed to allow you to see the patterns of your blood pressure day and night – revealing data that otherwise remains hidden. It works by using photoplethysmography, or PPG, which involves shining green light into the skin and measuring the light reflected back. Changes in blood volume with each heartbeat affect the amount of light reflected, allowing the sensor to capture the pulse’s wave. The proprietary algorithm then analyses these optical signals, converting them into blood pressure measurements that are presented in an easy-to-read graph within the Hilo App. 

Set-up couldn’t be easier. Once you’ve received your product, all you need to do is calibrate the band with the inflatable Hilo Cuff (which is provided) once a day for four days during your first week of use. This is important for accuracy, enabling the device to give you your absolute blood pressure values in mmHg. After this initial onboarding period, calibration is only required once per month, making sure accuracy isn’t compromised over time. 

Once set-up, the Hilo Band takes measurements whenever the in-built accelerator notes that you’ve been still for at least 5 minutes. It then gives an average measurement over a 2-hour period, as averaging is the standard practice that both physicians and hypertension guidelines recommend. 

Rest assured, the Hilo Band’s underlying technology has been rigorously tested in multiple clinical studies across a broad range of people. It’s also been endorsed by leading hypertension experts, has been granted the CE Mark as a Class IIa medical device and FDA approval. 

The information in this article is intended for educational purposes only and does not 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.

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