Not everyone is aware of, but over hydrating during long events is as dangerous as dehydration. There are many health conditions that can make us more prone to retaining possibly dangerous levels of fluid during long events (for that reason it’s very important to have regular checkouts with your doctor during your training leading up to a long event).
Up until a recent past, many athletes followed the advice to stay ahead of thirst and drink as much as possible during events. It’s normal during long training sessions and events to dehydrate to a certain extent.
The body under certain circumstances tries to adapt producing hormones that, among other things, try to keep the sodium/potassium equilibrium constant.
Does so by controlling the sodium excretion in the sweat and urine (sweat control happens at a slower rate than urine). The body also tries to get sodium from the bones, among other reactions, if necessary.
The body, under certain health conditions, may not control the sodium concentration in the blood as efficiently. So, as a result of these specific conditions, it may retain more liquid.
That fact, associated with an over consumption of liquids may cause the sodium outside the cells to dilute as the body starts to and since most of potassium is localized inside the cells it may cause tissue swelling (water passes freely). That condition is called hyponatremia.
If the tissue swelling happens in the brain it can be dangerous.
A few of the symptoms of hyponatremia may include; Weight gain during training (as it’s normal a certain level of innocuous dehydration), vomiting (from liquid accumulation in the stomach/intestines), headaches, low level of consciousness, photophobia (light sensitivity), hands and feet swelling (normally noticed as the event identification bracelet gets tighter), concentrated urine (as the extra cellular fluid gets lower).
1) The average weight loss during a marathon, for example, is 2-3 Kg. The mean liquid absorption by the intestines is about 600ml per hour.
2) Due to the great variability of sweat rates between individuals under specific circumstances it’s virtually impossible to come up with a general hydrating guideline that would be fit for everyone. For example, a runner competing under extreme cold/freezing weather may sweat as little as 100ml/hour as it would be an advantage (high sweat volume in this condition may freeze and cause hypothermia). On the other extreme, a 150Kg football player may sweat as much as 3000ml/hr under extreme hot conditions.
3) There are a few risk factors associated with the hyponatremia (low blood sodium concentration) development; Long events completed at slower paces (low heat generation as opposed to high fluid intake), the use of certain medications such as NSAIDS (a class of anti inflammatory drugs that can make an organism more sensible to the anti diuretic hormone), events that last longer than 4 hours.
Besides having medical support to uncover possible health issues always look up for a nutrition professional so you can get your personalized hydration right during long workouts (in preparation for long events).