In the story “Goldilocks and The Three Bears,” Goldilocks tries three bowls of porridge, each belonging to a different bear. Daddy bear’s breakfast is too hot, mummy bear’s breakfast is too cold, yet baby bear’s breakfast, the third bowl of porridge, is just right. While this is clearly a story for children, the concept of the ‘Goldilocks principle’, commonly used to describe when something is ‘just right’, has been taken and applied to numerous different areas including sport, education and science.
This analogy is also used in medicine, and of particular relevance is its application when thinking about blood pressure, or hypertension. For example, when considering the impact that weather has on blood pressure there is a clear ‘Goldilocks zone’:
- Weather that is too hot can raise blood pressure
- Weather that is too cold can raise blood pressure
- Weather that is neither too hot nor too cold is just right
In summary? If you have hypertension, the weather can impact your condition.
But what if you have hypertension and find yourself somewhere that’s too warm or too cool, either due to the climate or a lifestyle choice? What can happen to your blood pressure if you find yourself sweating or shivering?
In this article we’ll discuss how cold and hot weather cause your blood pressure to change, as well as outline the precautions that you can take to minimise any adverse effects on your health.
How Does Hot Weather Raise Blood Pressure? The Background Biology
You may have heard that being in a warm climate is ideal for those with hypertension, and there is truth in this – to a point.
Like most things in life, there is such a thing as too much. Heat is no different. On average, your blood pressure 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 to dilate, or widen, meaning that blood flow diverts to these vessels and excess heat can be dissipated into the surrounding environment.
Because vasodilation causes some blood vessels to widen, it’s easier to pump blood around the body as there is less resistance. This means that blood pressure reduces. Due to the reduction in blood pressure that vasodilation causes, many high blood pressure medications (antihypertensives) use vasodilation as their mode of action. However, while reduction of blood pressure can be a good thing if you are hypertensive, you still need to be careful of dehydration due to the heat, which can have serious consequences.
Dehydration May Be Subtle, But It Can Have A Big Effect
When you’re in a hot environment, your blood vessels maintain homeostasis by expanding, or undergoing vasodilation – this ensures that excess heat in your body is lost and your body temperature remains constant. However, if that expansion happens too fast, it can cause blood pressure to drop suddenly.
If a sudden pressure drop occurs your heart will compensate for it by pumping harder and at a faster rate to push more blood around the body. However, this can cause a blood pressure spike, which also isn’t good.
While these changes in blood pressure are natural and if you’re healthy your body can usually cope, it’s still a good idea to try and help your body when you can. For example, changes in your levels of hydration can have a significant, although subtle, impact upon your blood pressure, especially when it’s hot.
When it’s hot it can be the case that you’re unable to replace fluids at the same rate that you lose them through sweat, breathing, and urination, which can cause a fluid imbalance. In this situation overall blood volume decreases, which can mean that your tissues and organs don’t receive enough oxygen or nutrients to function normally. This can have disastrous consequences.
There are several stages to dehydration. In the first stage, as blood volume decreases blood pressure may also drop. However, this initial drop in blood pressure can cause a negative feedback loop:
- When blood volume is low or sodium levels in the blood are high after losing too much fluid, vasopressin, a key hormone for regulating blood pressure, is secreted.
- The presence of vasopressin causes blood vessels to narrow, raising blood pressure.
If you have a diagnosis of hypertension, avoiding fluctuation in blood pressure is a good idea, and you are best advised to avoid dehydration by ensuring that you drink enough fluids. The NHS recommends water or diluted squash as good options and that you drink 6 to 8 cups or glasses of fluid a day, although if you’re pregnant or breastfeeding you may need to drink more. Unfortunately, drinks containing caffeine and alcohol won’t suffice, as they can be diuretics, causing more water to be expelled from the body, further reducing blood volume and stimulating secretion of more vasopressin.
While this sounds scary, there is an easy way to tell how hydrated you are; if your urine is a pale yellow or clear color, you’re OK. If it’s darker yellow or light orange, it’s a warning sign that you need to drink more water.
“Record Heat” Warnings in 2025 Pose Extra Risk of High Blood Pressure
Risk of increased blood pressure from dehydration may become more prevalent as temperatures soar around the world due to climate change.
In recent years, there have been numerous reports of record-breaking heat, and it looks like 2025 will be no exception.
- January 2025 was the warmest on record globally, despite an emerging La Niña, which is a climate pattern causing cold weather across the tropical Pacific.
- Spring 2025 has been the warmest and sunniest on UK record, breaking several climate records.
- In the US, summer 2025 is predicted to be one of the hottest summers ever recorded.
- A report by the World Meteorological Organization (WMO) has suggested that global temperatures will break at least one annual heat record in the next five years
It’s impossible to ignore the growing trend. Unprecedented extremes of heat are occurring worldwide, across countries and continents. Climate experts predict that the Earth’s average temperature will increase by 4° C this century, based on greenhouse gas emissions continuing to rise at the same rate. While the implications of this change on the environment and planet are wide-ranging and extensively documented, our medical needs will also be affected. Particularly if you suffer from hypertension.
Warmer weather will lead to the bodily changes outlined above, as well as an increased risk of dehydration.
Why Cold Weather Can Also Affect Your Blood Pressure
We’ve established that hot weather can cause a raise in blood pressure, what about the cold?
Cold weather also impacts upon blood vessels, with some blood vessels (e.g. on the surface of your skin) reacting to cold temperatures by undergoing vasoconstriction. This is a protective biological feature and is designed to ensure that your body doesn’t lose too much heat by keeping blood close to your central organs. However, constricted blood vessels can result in higher blood pressure as the narrowing of vessels means that there is more resistance when your heart pumps your blood.
And this is backed up by evidence. A long-term study from the American Heart Association, published in Hypertension, has shown that blood pressure is affected by weather fluctuations. In this work, the researchers monitored the blood pressure of more than 16,000 people over 40 years. They mapped the blood pressure measurement for each person’s clinic visit with the weather conditions on the day of their visit.
They found that around 35% of the participants were classified as “temperature sensitive”, and were significantly affected by cold weather. These patients had a higher systolic blood pressure in follow-up visits than the non-temperature-sensitive participants, and were also identified as having a higher risk of mortality, or death, overall.
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The Winter Lifestyle Effect
While the weather itself can have an impact upon blood pressure in winter, changes in lifestyle during cold weather can also impact blood pressure. In winter, people tend to consume more calories and eat less healthily, as well as engaging in less physical activity, preferring to stay warm inside.
In addition, in winter we are exposed to less sunlight due to shorter day length, inclement weather and less intense sunlight. All of these factors mean that less serotonin, or ‘happy hormone’ is released. To combat this, people often look for other triggers for serotonin release. For example, carbohydrate-rich foods have been shown to boost serotonin levels, with foods such as chocolate, biscuits and potato crisps all being seen as mood-boosters. However, while they can offer a short-term pick-me-up, long term they can make you feel worse.
In summary? Colder temperatures. Less exercise. An inclination to eat more salty and sugary foods. All things considered, those with hypertension need to take extra care during the winter to keep their blood pressure in check.
Don’t Chance It! Track Your Blood Pressure 24/7 in Cold and Hot Weather
We’ve established that hot and cold weather can both pose risks to people with elevated blood pressure, or who have a diagnosis of hypertension. But in the UK, while 11.8 million (26.2%) adults in England had a hypertension diagnosis in 2017, it is estimated that for every 10 people diagnosed, seven remain undiagnosed and untreated. Furthermore, a study published in 2021 suggested that only two in five middle-aged people receiving treatment for hypertension have their blood pressure adequately controlled.
Rather than guessing or only measuring your blood pressure a couple of times a week, there is a more practical alternative. Hilo’s easy 24/7 blood pressure monitoring band saves you a lot of time and a lot of uncertainty.
Worn as a lightweight bracelet around your wrist, Hilo tracks your blood pressure day and night with automatic measurements, whatever the weather. Importantly, it takes away the hassle and the guesswork. You can also share readings with your doctor or family members if you wish, so relevant people are in-the-know.
Curious to find out more? Learn about Hilo.
Disclaimer: If you are concerned about your blood pressure, it is best to speak to your doctor. They can advise on the best way to manage it.
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