The summer of 2025 is among the hottest ever recorded. Indeed, with several episodes of heat wave that hit the country harshly, the situation has been tense in recent days. The consequences are direct, for health. Under high temperatures, the body transpires more, the water losses increase and the risks linked to dehydration too.
Watch out for the consequences of dehydration
You may not know it, but beyond heat strokes and fatigue, blood pressure can be directly affected by a lack of water.
“Good hydration plays a key role in regulating blood pressure”recalls Dr Gérald Kierzek, emergency doctor and medical director of True Medical.
Drinking enough is not only used to compensate for sweat. It is also an essential mechanism to maintain blood volume and allow the kidneys to properly regulate sodium. And therefore blood pressure.
How does dehydration drop the tension?
The most common situation in case of dehydration is hypotension. The lack of water decreases blood volume, which reduces venous return and cardiac flow. The body tries to compensate with an activation of the sympathetic nervous system, causing tachycardia, but that is not always enough.
Result: dizziness, fatigue, discomfort and sometimes systolic blood pressure less than 90 mmHg. “”The majority of cases of light to moderate dehydration cause hypotension“, Specifies Dr. Kierzek.
When chronic dehydration leads to hypertension
In certain situations, especially in the elderly or those who consume a lot of salt, dehydration can paradoxically promote hypertension.
“”The kidneys, trying to preserve water, retain more sodium, which increases the volove. In parallel, angiotensin II and ADH, hormones in our body, promote vasoconstriction“Details the doctor.”We observe this phenomenon especially in the event of chronic or severe dehydration, associated with a very salty diet“.
These cases remain less frequent but require medical supervision, sometimes with an adjustment of the antihypertensive treatment.
What to do in the event of a drop or increase in tension linked to dehydration?
The first answer in the face of heat-resistant hypotension is rapid rehydration: drinking 500 ml at 1 liter of flat water in half an hour, or using an oral rehydration solution if the losses are significant.
Assess the legs also helps improve venous return. To stabilize tension, some savory foods such as a broth or olives can also be useful.
Conversely, in the event of hypertension linked to insufficient hydration, it is advisable to regularly drink 1.5 to 2 liters of water per day, avoiding gas water rich in sodium.
In addition, foods rich in potassium such as bananas or spinach help compensate for excess salt.
Finally, concludes the doctor, “The best prevention remains regular hydration, adapted to age, activity and climatic conditions“.