by Ray Ogden
Hyponatremia has become a problem in high-endurance events such as marathons, ultramarathons, hiking and long military marches. Athletes need to drink regularly, for example during a long race, to prevent dehydration, but excess water can lead to hyponatremia.
Hyponatremia occurs when blood sodium concentration falls to an abnormally low level, prompting a rapid and dangerous swelling of the brain that can result in seizures, coma, and death.
Women appear more prone to hyponatremia than men. About half the women studied who finished the New Zealand Ironman triathlon developed hyponatremia, compared with 14 percent of the men, according to a report in the journal Medicine and Science in Sports and Exercise.
Young women, who have relatively high levels of estrogen, are 25 times more likely to die or have permanent brain damage as a result of hyponatremic brain swelling compared to men or postmenopausal women, who have relatively low levels of estrogen. In a report following the San Diego Marathon, 23 of the 26 cases were females. Hyponatremia was three times more common in women than in men in a study of finishers at the 1997 New Zealand Ironman triathlon.
Slow runners, triathletes, and cyclists have more time and easier opportunities to drink excessively. First time marathoners are high risk of hyponatremia because they are usually slow runners, and have more time to over drink. Excessive drinking is a key risk factor for hyponatremia, but it is possible to occur%97without excessive drinking%97in dehydrated athletes during very prolonged exercise as a result of large sodium losses in sweat.
What To Do?
There are no clear cut guidelines, and recommendations need to be individualized for each person. Some authorities recommend drinking less water to rebalance sodium and water intake. However, given the risk of dehydration and heat injury, this is not a practical recommendation. Others recommend increasing salt intake, and this seems a better idea. By ingesting more sodium, hydration with water is balanced and dilution of blood sodium does not occur.
Ideally, foods consumed during along race should be low fat, low protein, high carbohydrate, and provide a source of sodium. You need water, carbohydrates, and salt to survive a long race.
The American College of Sports Medicine (ACSM) recommends that individuals consume 500 ml (%7E 17 oz.) of fluid two hours before exercise and that they continue to consume cool drinks in regular intervals to replace water lost through sweating or the maximum amount that can be tolerated. ACSM also recommends adding electrolytes to fluid for prolonged intense exercise lasting longer than one hour.
The USATF further recommended that the replacement fluid should be sodium-containing sports drink in preference to plain water.
Ray Ogden has been a bodybuilder and runner for 30 years.
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