The serious  problem of overhydration

January 29th, 2022

The serious problem of overhydration

For many many years, the common approach when it came to hydration during racing was drinking way earlier than you’re getting thirsty. To almost drink as much as you possibly can, to compensate the amount of fluid you lost due to sweating.

That overhydration depicts a risk, that’s at least as dangerous as dehydration, wasn’t mentioned at all. More precisely, the scientific base wasn’t even laid yet.

The serious medical condition that can occur as a consequence of overhydration is hyponatremia. It describes a concentration of sodium in the blood that is too low. Even if it mainly appears as a side effect of conditions such as heart, kidney or liver diseases, the occurrence is likely to happen as an effect of inadequate fueling during racing.

That’s because many athletes substitute their loss of fluid with exclusively water, which can have devastating impacts. Excessive drinking further dilutes the sodium levels, which are already reduced by sweating. It is quite a common theory that athletes should drink enough in competition long before they feel thirsty and do so simply out of habit - which of course significantly increases the risk of hyponatremia. It is not for nothing that the feeling of thirst is a clear body signal demonstrating the need to drink.

Symptoms of exercise-associated hyponatremia:

  • Impaired exercise performance
    • This occurs at quite low levels of weight gain and is due either to swelling of the brain cells or to an increased pressure within the brain, either or both of which impair brain function.
  • Nausea and vomiting
    • These symptoms result either from an increased intracerebral pressure caused by brain swelling or the presence of a large volume of unabsorbed fluid in the stomach and intestine, or perhaps a combination of both. Especially the vomiting of large volumes of clear fluid (water) can occur only if the rate of fluid intake has been excessive. Similarly, the presence of excess unabsorbed fluid in the gut will cause a sensation of fluid sloshing around in the intestines. Neither of these symptoms can occur in dehydration, since in dehydration the content of water lying free in the intestine is reduced.
  • Headache
    • This results from the increased intracranial pressure caused by brain swelling in exercise-associated hyponatremia. Since dehydration reduces the fluid content of the brain, in cannot cause headache by this mechanism. Whereas headache might be an expected feature of hyponatremia, there is no reason for it to develop in dehydration. Headache is not listed as a common symptom in cholera, the disease causing the most rapid onset of profound and life-threatening dehydration in humans.
  • Altered level of consciousness
    • Athletes with a moderate level of hyponatremia become sullen, sleepy and withdrawn; they avoid social interaction, close their eyes, and turn away from the light seemingly because they have photophobia (dislike of light). When addressed, they appear confused and somewhat dull; they are unable to hold a conversation of substance. They have difficulty concentrating and speak only when addressed directly. They have no interest in conversation. They appear to be either intoxicated or to have suffered a head injury causing concussion. Pivotal in those with mild hyponatremia is the fact that these symptoms can be reversed almost miraculously within minutes by the administration of a hypertonic (3-5%) saline solution. Important to mention is that these symptoms do not appear with athletes that suffer from dehydration – it’s therefore distinctive.
  • Seizure (convulsion)
    • This is caused by a marked increase in intracerebral pressure. Since dehydration reduces the intracerebral pressure, it cannot cause a convulsion by this mechanism. People who are lost in the desert without water do not develop seizures. Instead, they become confused and lapse into coma, most likely because of a progressive reduction in blood flow to the brain associated with the accumulation of toxic substances in the blood secondary to kidney and liver failure. Since the mild levels of dehydration encountered in ultramarathon runners and Ironman triathletes do not cause kidney and liver failure, so coma and convulsions in endurance athletes are not caused by dehydration.
  • Bloating and swollen hands, legs, and feet
    • These aspects are usually first noted by the athlete’s spouse or other relative or friend. Athletes may notice that their watch straps or race number bracelets become tighter as they become progressively overhydrated. In contrast, dehydration will cause the opposite – athletes will look as if they have become thinner, and their watches and race number bracelets will become less tight.
  • Muscle cell breakdown with the development of acute kidney failure
    • Although this symptom appears rather exceptionally, reports and studies have shown a direct correlation between overdrinking and muscle cell breakdown with the development of acute kidney failure.

The following are symptoms that are not related to either dehydration or hyponatremia:

  1. Dizziness and fainting
    • Both of those symptoms are caused by an inadequate blood flow to the brain as the result of reduced blood pressure. An altered blood flow to the brain dies not occur in hyponatremia or dehydration at the mild levels measured in endurance athletes. Post exercise dizziness is due to hyponatremia, which is unrelated to the level of dehydration in athletes but is caused by an impaired regulation of the circulation when exercise terminates suddenly.
  1. Muscle cramping
    • This is a separate condition, that is caused by an altered nervous control of the muscles and is not due to overhydration, dehydration or sodium deficiency in salty sweaters.
  1. Wheezy breathing
    • This is a feature of asthma or similar respiratory conditions and is unrelated to overhydration or dehydration. Athletes with pulmonary edema due to hyponatremia may complain of shortness of breath and cough up a blood-stained sputum. Dehydration does not cause pulmonary edema.

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