Dehydration is often dismissed as simple thirst, but when the body loses more fluid than it replaces, it can affect the circulatory system and heart function. The risk is higher during hot weather, exercise, fever, vomiting, diarrhoea, or prolonged sweating.
1. Blood volume can decrease
A large portion of blood is water. When the body becomes dehydrated, blood volume may fall, making it harder for the heart to circulate blood efficiently.
2. The heart may beat faster
To maintain blood flow despite reduced fluid volume, the heart may compensate by increasing the heart rate. This can cause palpitations or a feeling that the heart is racing.
3. Blood pressure may drop
Dehydration can contribute to low blood pressure, particularly when standing up suddenly. This may lead to dizziness, weakness, blurred vision, or even fainting.
4. The blood may become more concentrated
Fluid loss can make the blood more concentrated. In people who are already at risk of cardiovascular problems, severe dehydration may contribute to circulatory stress and increase the risk of complications.
5. The kidneys and heart are closely connected
When the body lacks fluid, the kidneys try to conserve water. This affects the body’s fluid and electrolyte balance, which can indirectly place additional stress on the cardiovascular system.
6. Electrolyte imbalance can affect heart rhythm
Severe dehydration may disturb electrolytes such as sodium and potassium, which are important for normal muscle and electrical activity—including the heart. Significant electrolyte disturbances can potentially cause abnormal heart rhythms.
Who should be especially careful?
- Older adults
- Infants and young children
- People with heart or kidney disease
- People taking certain medicines, such as diuretics
- Athletes and people working in extreme heat
- Anyone experiencing prolonged vomiting or diarrhoea
Warning signs of serious dehydration
Extreme weakness, confusion, fainting, very little or dark urine, rapid heartbeat, severe dizziness, or inability to keep fluids down should not be ignored. Severe dehydration may require urgent medical attention.
How to prevent it
Drink fluids regularly instead of waiting until you feel extremely thirsty. During heavy sweating or prolonged illness, replacing lost electrolytes may also be necessary—but people with heart or kidney conditions should follow their doctor’s advice because excessive fluid or electrolyte intake can also be harmful.
Important: Mild dehydration is common and usually reversible, but severe dehydration can become a medical emergency. The key message is simple: hydration supports not only your energy and temperature regulation, but also your circulation and cardiovascular system.
