From the Guidelines
Dehydration leads to headache primarily by reducing blood volume, causing decreased blood flow to the brain, and triggering pain receptors in the meninges. When the body lacks adequate fluids, the brain can temporarily contract or shrink from fluid loss, pulling away from the skull. This reduction in blood volume is associated with a decrease in plasma volume and an increase in plasma osmolality, as seen in exercise-induced dehydration 1. Additionally, dehydration causes electrolyte imbalances that affect nerve function and can impair the brain's ability to regulate pain. Blood vessels in the brain may also narrow in response to fluid loss, further restricting blood flow and oxygen delivery, which can intensify headache pain. The body's stress response to dehydration increases cortisol and other stress hormones that can trigger or worsen headaches. To prevent dehydration headaches, it is essential to drink water consistently throughout the day, aiming for about 2 liters daily for older men and 1.6 liters daily for older women 1. If you already have a dehydration headache, drink water slowly but steadily, and consider adding electrolytes through sports drinks or foods. Most dehydration headaches resolve within 30 minutes to 3 hours after rehydrating properly. It is also important to note that older adults are at a higher risk of dehydration due to age-related physiological changes, such as a blunted thirst response and reduced total body water 1. Therefore, it is crucial to encourage older adults to consume adequate amounts of drinks, including water, milk, tea, coffee, and fruit juices, to prevent dehydration and related headaches. In particular, older adults living in residential care may require closer monitoring of their fluid intake, as they may be at a higher risk of dehydration due to factors such as memory problems, dysphagia, and physical access to drinks 1.
From the Research
Dehydration and Headache
- Dehydration can lead to headache, as it disrupts the body's fluid balance and can exacerbate underlying medical conditions such as primary headache disorders 2.
- Dehydration alone may cause headache, but it often worsens existing conditions dependent on fluid balance, including orthostatic and "coat-hanger" headache due to autonomic disorders 2.
- Maintenance of euhydration can help treat certain types of headaches, such as those caused by autonomic disorders, and prevention of fluid losses can mitigate secondary headaches provoked by dehydration 2.
Mechanisms of Dehydration-Induced Headache
- Dehydration can affect brain structure, with studies showing expansion of the ventricular system, particularly in the left lateral ventricle, after acute dehydration 3.
- The loss of body water and electrolytes can disrupt normal brain function, leading to headache and other symptoms 4.
- Dehydration can also lead to a decrease in blood volume, which can reduce blood flow to the brain and contribute to headache development 2.
Treatment and Prevention
- Maintaining adequate hydration is essential for preventing dehydration-induced headaches, and individuals should be aware of the signs and symptoms of dehydration to seek medical attention if necessary 4.
- Treatment of dehydration typically involves replenishing lost fluids and electrolytes, and may include intravenous fluids or oral rehydration therapy 4.
- In some cases, medication such as paracetamol or aspirin may be used to treat headache symptoms, but these should be used under medical supervision and in conjunction with hydration therapy 5, 6.