For those running The Honolulu Marathon, especially for the first time, you will hear all kinds of advice. One of the more common tips is to drink a lot of water to hydrate in the days leading up to and also during the event.

It sounds simple, and it is true that you need to be well hydrated to help prevent fatigue, but figuring how much and what to drink is tricky.

Hydration is even more important in Honolulu than on the Mainland because of our warm weather.

Holly Pelletteri, 42, has run 13 marathons. Each one had been on the Mainland, except for last year's Honolulu Marathon.

"I became very dehydrated despite my 'usual' hydration techniques I've used for past Mainland marathons. I started feeling poorly about mile 15; I was nauseated, had a headache and boy was my skin salty! I was about 15 minutes off my goal time."

What many seem to overlook is that over-drinking can be just as bad as drinking too little. Over-hydrating can lead to a hyponatremia. This is a condition when the body's sodium levels decrease when hydrating with too much low sodium liquids, such as water.

Marathoners are at risk to this because they also lose a lot of sodium in sweat. Hyponatremia can lead to the same type of symptoms as dehydration such as nausea, fatigue, vomiting, dizziness, weakness and in severe instances, seizure, coma and death.

Hyponatremia is a result of the body not being able to absorb the fluids properly because it does not have enough sodium. To put it simply, the body is over diluted.

WATCH SODIUM LEVELS

To help prevent this dangerous condition, hydrate by drinking sports drinks instead of water. Sports drinks have sugars and electrolytes so they will help keep your sodium levels more in balance and absorb liquid into the body easier.

If you don't have high blood pressure or a prescribed salt restrictive diet, then add salt to your foods in the few days before the marathon. You can also take electrolyte or salt tablets.

During the marathon, use sports drink as your liquid of choice. If you don't like sports drinks, then you can take sports gels that have sodium, or even salt tablets. Make sure you drink enough water to wash them down.

Figuring out your sweat loss can help you determine your hydration needs.

To find out how much you sweat, weigh yourself before a long run. Keep track of how much you drink during your run. Jump on the scale right after you finish the run with exactly what you wore for the workout.

The difference in your weight before and after your run measures your fluid loss. If you lose too much fluid, it may impair many body functions since there is a loss of water from cells and from the blood. Everything must work harder to deal with the condition. Even brain function has been shown to be impaired at 1 percent to 2 percent dehydration.

For every pound lost, you should drink about a pint of fluid. Ideally, your weight should remain about the same afterward.

WEIGHT LOSS ALERT

The hotter the weather, the more important it is to maintain hydration. Whereas a 2 percent weight loss may not affect performance in a cool climate, it can hurt your performance on a hot day. A 2 percent to 3 percent loss in weight could mean a noticeable drop in performance, but it also depends on how much carbohydrates you have stored in your body.

Dr. Alan Titchenal of the University of Hawai'i does research focusing on nutrition and human performance.

"The American College of Sports Medicine puts the number at one to two percent of body weight as the degree of water loss that starts to impair performance," he said. "How well you carbo load determines how much water your body is holding at the start of a marathon.

"Theoretically, a carbo-loaded athlete can easily be carrying a pound of glycogen that will be burned up during a marathon. Since glycogen binds about three times its weight in water, about three pounds of water also will be freed up and available for sweat loss. So, depending on the athlete's body size, a two- to three-pound weight loss should not be excessive. An athlete who is not carbo loaded at the start has less water reserves and may develop problems at a lower level of water loss."

DON'T OVERTHINK IT

Hydrating your body for the marathon is simple and should not take too much thinking, just a lot of remembering.

"During the early morning, eat and drink what you have found worked well before your long training runs," said Titchenal, who has run 20 Honolulu Marathons. "Don't try anything new.

"This typically will involve eating high carbohydrate/low fat foods along with normal amounts of fluid. Stay normally hydrated the day before the marathon and the morning of the marathon. You can't water load like you can carbo load. Excess water just goes right through the body, increasing urine production. However, fluids consumed during the 15 minutes prior to the race start are likely to be conserved for sweat production rather than urine production because the kidneys slow down urine production during exercise."

During the race, drink eight to 10 ounces at every aid station. It is also important to consume fluids at regular intervals, but don't drink enough to gain weight.

Getting fluid has been a main strategy in all seven of the marathons that Kane Ng-Osorio has completed.

"I stop at all the aid stations, even the early ones when I don't think I need liquids and take them anyway," Ng-Osorio said. "It is better for me to take these fluids when I don't think I need them rather than waiting too late in the race."

By understanding your body's hydration needs, it can keep you going strong for 26.2 miles.

Toni Kruse, 37, can attest to that.

"I definitely feel that my performance is based on how well I hydrate. If I go into race day a little "empty" (dehydrated) I am in big trouble. It's difficult to play 'catch-up.' " said Kruse, who will be running her third marathon.

Jonathan Lyau is a 12-time kama'aina winner of the Honolulu Marathon. He will be writing a series of articles leading up to The Honolulu Marathon.