Runners, hikers, bikers, even soldiers on long maneuvers should think twice before reaching for that water bottle: A study confirms that drinking too much can be dangerous, even deadly, for endurance athletes. Researchers who studied 488 runners in the 2002 Boston Marathon found that 62, or more than one in eight, had a serious fluid and salt imbalance from drinking too much water or sports drinks. Three of them had extreme imbalances. One 28-year-old woman died after the race from the condition, called hyponatremia, in which the excess water dilutes the salt level in the body too much. "More is...