Dr Pauline Swift, chair of Blood Pressure UK, has warned that hot weather can put extra strain on the body, particularly for people with high blood pressure, heart and kidney conditions, or those taking blood pressure medication. As the UK experiences its third heatwave of the year, with temperatures rising across England, Wales, Scotland and Northern Ireland, understanding the effects of heat on blood pressure is crucial.
How heat affects blood pressure
Dr Swift explained that sweating more in hot weather can lead to dehydration, which may cause blood pressure to fall. This can leave people feeling dizzy, light-headed, tired or unwell. High temperatures also cause blood vessels to widen, especially near the skin, to release heat, which can further lower blood pressure. Some medicines, including diuretics and certain blood pressure treatments, can make it harder for the body to cope with sudden heat.
Sweating and dehydration reduce the amount of fluid circulating in the bloodstream, known as blood volume. The heart may need to beat faster and work harder to maintain blood flow, particularly during significant heat stress. Certain medications, such as beta blockers, can limit how much the heart rate can rise in response to heat, increasing the risk of dizziness and low blood pressure.
Medication advice during heatwaves
Dr Swift emphasised that people should continue taking prescribed medicines as directed and seek advice if they are concerned about how heat may affect their treatment. Diuretics can increase fluid loss, while other medicines that affect blood vessels or kidney function may raise the risk of dehydration or low blood pressure. However, stopping medication without medical advice can be dangerous.
The level of risk depends on how hot conditions become and how long they last. The Met Office noted that conditions this week are expected to be less humid than during June's heatwave, with lower peak temperatures and fewer exceptionally warm nights. But many places are likely to experience several consecutive days of hot weather.
Met Office warning
Met Office deputy chief forecaster Steven Keates said: "Parts of the UK are entering heatwave conditions: the third heatwave in the UK so far this year. However, unlike the May and June heatwaves, we are not expecting this heatwave to be record-breaking. Much of England and Wales will be hot, and the heat will extend to parts of Scotland and Northern Ireland too, though here peak temperatures are more likely to be in the upper 20s Celsius. With high UV and high temperatures, people should take the usual precautions with the heat and the sun."
Simple steps to stay safe
Dr Swift recommended simple steps to counter the effects of heat on blood pressure. She added: "The key is to stay cool, drink regularly rather than waiting until you feel thirsty, limit alcohol and avoid strenuous activity during the hottest part of the day. Keep an eye on symptoms such as dizziness, headache, dark urine or confusion, and speak to a pharmacist or GP if you are worried about how the heat may affect your medication. Do not stop prescribed medication without medical advice."
