Dehydration is commonly believed to trigger headaches – from those experienced during a hangover to severe, recurring migraines. Unsurprisingly, headache is one of the most common symptoms of dehydration.
Although why this happens isn’t understood completely, one common belief is that the drop in blood volume caused by dehydration – remember that water is a major component in plasma – decreases the flow of oxygen and blood to the brain. Plus, dehydration reduces the amount of electrolytes in the body, depriving our brains of these vital nutrients. This, in turn, is thought to contribute to those nagging headache symptoms.
Many headache groups agree, too. The Migraine Trust, American Headache Society and the American Migraine Foundation include dehydration on their lists of possible headache triggers, and they all advise sufferers to drink plenty of fluids.
But what does the research say about dehydration and migraines? Is there any real evidence that dehydration causes headaches?
What Is a Water-Deprivation Headache?
Researchers have been studying this subject for years, and there’s varying levels of evidence showing a clear link between the two. One thing is clear: Dehydration, however slight, negatively affects the brain.
For example, mood and adverse cognitive effects have been observed in people who were just mildly dehydrated. One 2012 study[i] looked at the effect that 1.4 percent dehydration – which is about the point we start to feel thirsty – had only 25 female participants. When dehydrated, the participants were more likely to experience headache symptoms, as well as degraded mood, lower concentration and difficulty performing tasks.
Another study[ii] examined these so-called “water-deprivation” headaches, but instead examined if drinking more fluids could relieve symptoms. The study followed 34 subjects who were experiencing headaches, and they found that about 2 cups of water relieved the symptoms for 22 patients within a half hour. An addition 11 subjects felt total relief 1 to 3 hours later after drinking about 3 cups of water.
Does Dehydration Trigger Severe Migraines?
For people who experience regular migraine headaches – roughly 36 million Americans – researchers have also found evidence that dehydration can trigger episodes.
A 2005 study[iii] revealed that patients who drank an additional liter of water each day experienced fewer hours of migraine pain. The study followed 18 migraine patients. One group was given a placebo, and the other group was advised to drink an extra 1.5 L of water per day, (which resulted in these patients adding an additional liter of water to their normal drinking.) After two weeks, the “more water” group experienced 21 fewer hours of migraine symptoms and they reported their episodes were less intense.
Although more research needs to be done, these early trials are convincing. Thus, preventing your next headache might be as simple as avoiding dehydration.