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Is Drinking Two Bottles of Water per Hour Too Much?

The Surprising Truth about Over-Hydration. What Runners and Cyclists Need to Know

Runner Grabbing Water BottleHave you ever experienced that dull throbbing headache while on a long run or ride?  Maybe cramps or dizziness started to set in.  Could your body be reacting to dehydration?  Or could you actually be over-hydrating?

While athletes know hydration is critical to their performance, many may not know the dangers of overdoing it.  Most at-risk are endurance athletes, who may consume too much water too fast over long periods to replace fluids lost through excessive sweat. Understanding the dangers and prevention of over-hydration is important.

OverHydrating and Sodium Imbalance

Rapid intake of too much water can lead to water intoxication and to a related problem resulting from the dilution of sodium in the blood called hyponatremia, or overhydration.  This condition occurs when your kidneys – which control the balance of water and salt in our bodies – cannot flush out the deluge of water fast enough.

As your blood sodium drops (through sweat, replaced by fluids), the excess water consumed seeks to move inside the body tissue cells where the concentration of salt and other dissolved substances is higher.  When this happens, our cells swell like balloons.  While most cells can handle the swelling, our brain cells cannot because they are restricted within our skull, where there is no room for expansion.  It is the swelling of the brain that causes most of the symptoms of hyponatremia.

Symptoms of OverHydration

The first sense that you may be overhydrating is when your shoes start to feel too tight and your ring starts cutting into your finger.  As the swelling increases pressure in the brain, you will notice headache, personality changes, confusion, irritability, and drowsiness.  These symptoms can be followed by difficulty breathing as your chest constricts, muscle weakness, cramping, nausea, vomiting, thirst, and a dulled ability to perceive and interpret sensory information.  The cells in the brain may swell to the point where blood flow is interrupted, resulting in cerebral edema.  The swelling may also apply pressure to the brain stem causing central nervous system dysfunction.  Both cerebral edema and interference with the central nervous system are dangerous and could result in seizures, brain damage, coma or death. 

Misdiagnosing OverHydration Symptoms Can be Tragic

One of the particularly vexing problems for endurance athletes and race medical staff is that many of the symptoms of over-hydration mirror those of dehydration:  throbbing headache, nausea, cramps, and dizziness.  Misdiagnosing these symptoms as dehydration can dangerously exasperate the condition, if fluids- instead of sodium concentrate – are pushed as treatment.

Reasons Why Endurance Athletes are At-Risk for OverHydration

Brain swelling from hyponatremia has caused the death of several marathon runners in previous years.  Studies suggest up to 25 percent of marathon finishers have some evidence of its effects.

Three key factors can lead to this condition:

  1. Guzzling water:  The danger of drinking too much water is not so much about how much water you drink, but how fast you drink it.  Runners that quickly guzzle large amounts of water as they pass through water stations tend to be more at risk.
  2. Excessive sweat:  Athletes who train or compete over long periods (over 2 hours) are more at risk of hyponatremia due to the extended periods of sodium loss through sweat production; particularly in hot and humid conditions.
  3. Physical stress:  The physical stress of endurance events can exasperate the water imbalance.  Stress causes your body to increase secretion of vasopression, an anti-diuretic hormone.  This causes your body to conserve water, even as you are drinking excessive water.

Because of the prevalence and seriousness of this condition in long distance runs, medical personnel at marathon events are trained to suspect water intoxication immediately when runners collapse or show signs of confusion.

Increased Risk for “Back of the Pack” Runners and Cyclists

The occasional endurance athletes – the weekend enthusiasts who may get involved with charity runs and rides and enjoy long-distance training with friends – have been found to be most at risk.  These athletes – particularly the women – are more likely to follow the old advice to drink as much water as possible.  Because they are slower than the elite athletes and likely not as focused on the clock, they tend to take more time and opportunity to slow up and guzzle water at each feed zone.    And, while both groups may travel the same distance, the back of the packers take much longer to finish the race, again giving opportunity to drink more water.

In contrast, elite athletes, such as the marathon runners, are said to go too fast to drink too much.  As one doctor noted in The Physician and SportsMedicine, top runners rarely drink more than two or three liters (under 100 ounces) during a marathon, while the slower runners were found to drink as much as 6-7 liters (more than 200 ounces).  Also the elite runners worked up much more of a sweat, further reducing the chances of too much water in the body.

How Much is too Much Water?Relaj Water Bottle

There’s a careful balance between drinking enough water to stay hydrated, and drinking too much.  Every person is unique in their size, athletic intensity, hormonal levels and sweat rates.  MayoClinic.com advises athletes to drink only as much fluid as they lose due to sweating during a race — usually no more than about 34 ounces (about 1 liter) of water an hour during extended exercise, which is less than 2 standard (20 ounce) water bottles per hour.  If you’re not thirsty and your urine is pale yellow, you are likely getting enough water.

The American College of Sports Medicine recommends weighing yourself before and after exercise to estimate your fluid losses, then drinking enough to stay within 2 percent of your starting weight.  Some marathons now have weigh stations available at check-in and at various points along the course, so that both participants and the medical team can record weight gain or loss.

Do Sports Drinks Help Prevent OverHydration?

Sports drinks are designed to replace electrolytes as you replace fluids, and have been found to offer benefits to athletes.  However, there is no evidence that the consumption of sports drinks can prevent water intoxication.  Instead, it’s believed that drinking too much of these drinks can dilute your blood almost the same as water will, because the sodium concentration in sports drinks are closer to that of water than of blood.


I had always heard you should stay ahead of your thirst; in other words, if you wait until you are thirsty to drink, it’s too late.  However the current advise from the USA Track & Field organization is you should only drink when you are thirsty, to prevent becoming over-hydrated.  For endurance athletes, being aware of this is one of the most important steps towards prevention.

How do you gauge your hydration levels during endurance events?  Let us know what works for you.



USATF announces major change in hydration guidelines, usatf.org
Exercise Associated Hyponatremia, ASNJournals.org
Sodium – Salt – Needs for Ultra-Endurance Athletes, SportsMedicine.About.com
Hyponatremia: Prevention, MayoClinic.com
Are You Drinking Too Much Water? MensHealth.com
New Advice To Runners: Don’t Drink The Water, NYTimes.com
Hydration Angst, NYTimes.com
Water-Intoxication, Wikipedia.org

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