Can Drinking A Lot Of Water Give You A Headache?

Overhydration can lead to a situation in which the blood concentration of sodium -- one of the chemicals in salt -- gets too low. This condition is called hyponatremia, and a headache is just one of the symptoms. You might recall a news incident in which a radio show had a water drinking contest to win a Wii. A woman contestant lapsed into a coma and died after drinking an excessive amount of water.

Water Balance

On average, adults are 70 percent water. Fat has a lower water-holding capacity than muscle, so people with a higher percentage of body fat will contain proportionaly less water. Under normal conditions, an adult can drink and absorb up to one quart of water per hour, and through a combination of urination, respiration and perspiration, lose the same amount. Problems occur when you drink more than you can excrete.

Sodium Balance

The blood concentration of sodium is tightly managed. Consume too much salt and urine gets saltier; consume too little and sodium is conserved. All of this is accomplished by your kidneys, which have a sensitive salt measuring and managing system. This balance can be overturned by drinking too much water, especially if consumed too fast and not accompanied by salt-containing foods. When blood sodium gets too low, cells swell. Swollen hands and ankles are not a health risk, but swelling of the brain causes increased pressure inside the skull.

Hyponatremia

Standard blood tests define the normal range for sodium in blood as 136 to 145 milliequivalents per liter, abbreviated as mEq/L. Sometimes the units will be millimoles per liter, abbreviated as mmol/L, but the number range is the same. Below 135 mEq/L is considered hyponatremic and below 130 mEq/L seriously hyponatremic. With old age there are other causes of hyponatremia, including kidney failure, heart disease or liver failure, but for young to middle-aged people, drinking too much water or sports beverages is the most common cause. Initial symptoms include headache, nausea, vomiting, restlessness and irritability. Symptoms can progress to lethargy, decreased consciousness, epileptic-like seizures, coma and death.

Who is at Risk?

Athletes participating in endurance events and people who consume the illegal recreational drug ecstasy are at risk for drinking too much water. According to an article in the December 2005 issue of "Proceedings of the National Academy of Science," Timothy Noakes and co-authors reported that of 2,135 athletes in endurance events, 11 percent were heavier at the end of the event than at the start. This happens because many athletes follow the mistaken advice to drink before they are thirsty. Drinking sports hydration beverages instead of water does not fully protect against risk of hyponatremia, as the sodium content is too low to compensate for the excess water.

Garland Campbell's review in the November 2008 issue of the "Clinical Journal of the American Society of Nephrology" stated that side effects of ecstasy include dry mouth and thirst. Rave-type parties where ecstasy use occurs might have relax-and-recover rooms away from the loud music, with supplies of bottled water or sports hydration beverages. For unknown reasons, women are more at risk of hyponatremia from participation in exercise events or ecstasy use.