Does Drinking Water Help Headaches? What the Only Trial Says
Updated: 1 day ago
"Drink some water" is the first thing anyone says about a headache. It is cheap advice, and it is worth asking whether there is any evidence behind it. There is, but less than the confidence of the advice suggests. Here is what the research actually measured, and what the numbers work out to.
The one randomized trial
In 2012, Family Practice published a randomized trial on the effects of regular water intake in patients with recurrent headaches, run in Dutch general practice by Spigt and colleagues. It is, as far as we can find, the only randomized controlled trial that tested extra water as a headache treatment.
The setup:
102 patients with recurrent headaches (at least two moderate episodes or five mild ones a month) who drank less than 2.5 liters of fluid a day
50 were assigned to a control group and 52 to a water group
Both groups got written advice on stress reduction and sleep
The water group was also told to drink 1.5 liters more water each day
Follow-up lasted three months
The results:
Quality of life on the Migraine-Specific Quality of Life scale improved 4.5 points more in the water group, with a 95 percent confidence interval of 1.3 to 7.8
47 percent of the water group reported much improvement (6 or higher on a 10-point scale) versus 25 percent of controls
Days with at least moderate headache did not change in any relevant way
What those numbers mean
The paper reports the percentages. It does not translate them into the measures clinicians use to judge whether a treatment is worth trying. We did, using the trial's own figures.
Absolute difference in "much improved": 47 minus 25 is 22 percentage points.
Number needed to treat: 1 divided by 0.22 is about 4.5. For every five people who added 1.5 liters of water a day, roughly one more reported much improvement than would have without it.
Relative difference: 47 divided by 25 is 1.9. The water group was almost twice as likely to report much improvement.
The dose, in everyday units: 1.5 liters is about 6.3 standard 8-ounce glasses a day. Over the three-month trial, that is roughly 135 liters per person, or about 570 glasses.
A number needed to treat of 4.5 is good by the standards of lifestyle interventions. The catch is in what improved: how people felt and rated their lives, not the count of headache days.
The honest caveats
A 2015 critical appraisal of this trial, published in the Journal of Evaluation in Clinical Practice, called the evidence limited: the trial was underpowered, only partly blinded (you know whether you are drinking more water), lost a substantial share of participants before the end, and the objective outcome did not move. The subjective improvement could partly reflect the fact that people who were told to do something and did it felt better for it. The appraisal's conclusion, and ours, is that a larger trial is needed before anyone can claim water prevents headaches.
What the trial does support is the authors' own modest recommendation: the intervention costs nothing, carries no risk for healthy people, and almost half of the people who tried it felt much better. Trying it for a few weeks is reasonable.
The other direction: taking water away
There is better evidence that removing water produces headaches. A 2012 study in the Journal of Nutrition, Mild dehydration affects mood in healthy young women, put 25 young women through three eight-hour sessions: one normally hydrated, one dehydrated by exercise, and one dehydrated by exercise plus a diuretic. The dehydration was mild, averaging 1.36 percent of body mass.
At that level, participants reported headache, lower vigor, more fatigue, worse total mood, reduced concentration and higher perceived difficulty of tasks. Most measures of actual cognitive performance did not drop. In other words, a water deficit small enough that most people would not notice it produced the symptoms people complain about on a bad afternoon.
Our arithmetic on the dose: 1.36 percent of a 60-kilogram woman is 0.82 kilograms, roughly 0.8 liters of fluid, about three and a half glasses of water. That is a deficit you can accumulate by skipping drinks from breakfast to mid-afternoon.
Putting the two together
Being about three glasses behind is enough to bring on headache and fatigue, per the dehydration study.
Adding about six glasses a day doubled the share of chronic headache patients who felt much better, per the trial, without changing headache frequency.
Neither study says water replaces a diagnosis. Recurrent or severe headaches need a clinician.
The practical gap in both studies is timing. The deficit builds silently through the day, and the trial's intervention worked only for people who actually drank the extra 1.5 liters, spread across the day, for weeks. Nobody manages that from memory.
Water Textapp handles the memory part. Set a goal, text a number when you drink, and if you are behind by late morning or mid-afternoon it texts you. Those two check-ins land exactly where the deficit in the dehydration study would have built up.
A three-week test
Set a daily goal that adds roughly six glasses to what you drink now. If you currently drink two, set eight.
Log every glass so you know whether you actually hit it. Self-reports in the trial were the weak point; your log fixes that for you.
Keep a simple note of headache days and how you felt.
After three weeks, compare. If you are in the group the trial describes, you will know.
Try it by text
Text Hi to (646) 640-0771 to start Water Textapp. It asks for a goal in glasses, and then you text a number each time you drink. It keeps the total, tells you what is left, and checks in twice a day until you reach it. It works on any phone that can text, with no app to install. Your first 20 messages are free, then one $9.99 a month subscription covers every Textapp. Details at textapp.co/apps/water.
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