Hydration and Hyponatremia
By Leah Moore Thomas, MS, RD/LD
Summer is here, and if your exercise regime includes prolonged outdoor activity,
such as running or cycling, you’ll have to make some adjustments. While
proper hydration is an important practice all year long, it becomes more difficult
in the heat of summer. You can lose anywhere from 24 fluid ounces (three cups)
to 80 fluid ounces (10 cups) of fluid per hour just through sweat. Even mild
dehydration can cause uncomfortable and sometimes dangerous physical consequences.
For years we were instructed to drink as much fluid as our bodies could tolerate
during prolonged exercise. However, in more recent years, this recommendation
has been re-evaluated due to an increase in the incidence of hyponatremia.
Hyponatremia is a disorder in fluid-electrolyte balance that results in abnormally
low plasma sodium concentration. A prolonged decrease in plasma sodium concentration
disrupts the osmotic balance across the blood-brain barrier, resulting in a
rapid influx of water into the brain. This causes brain swelling and can lead
to a myriad of severe neurological responses, such as confusion, seizure, coma
and if severe enough, death. While hyponatremia can be caused by many different
factors, the cause that most concerns active individuals is excessive consumption
of water during prolonged exercise. Water replaces fluid lost through sweat,
but it does not replace sodium that sweat contains. By taking a few precautions
and by observing certain cues from your body, you can avoid hyponatremia.
Drink to maintain hydration. Beware of overhydration. A simple way to monitor
hydration needs is to regularly weigh yourself before and after exercise. For
every pound of weight lost, you need to consume approximately 16 ounces of fluid.
A weight loss greater than two pounds is indicative of dehydration and is a
red flag indicating that you should consume more fluids during your next exercise
session. Gaining weight during exercise is a sure sign of over consumption,
in which case your fluid intake should be reduced during subsequent sessions.
Maintain a salty diet. Especially during the summer months, as sweat losses
increase, consider adding salt to your food at meals or choosing salty snacks
such as pretzels. You should pay particular attention to this if you tend to
lose more sodium in your sweat than the average individual. If you notice that
your skin and/or clothes develop a white residue during runs, this is probably
you. Although this advice goes against the FDA’s recommendation, consider
that only 30 percent of the general population is “salt sensitive,”
meaning that their blood pressures are likely to increase due to sodium consumption.
Use sports drinks. By consuming at least some sports drinks during and/or after
your workout, you are not only replacing fluids, but electrolytes as well as
carbohydrates. Eating energy gels, bars or other solid foods also can help.
If you are one of those “sodium losers” described above, you might
even want to consider an electrolyte tablet to be on the safe side. You might
find these at specialty sports stores.
Following these precautions will help protect you and your patients against
hyponatremia. However, because there is no guarantee, it is still important
that you listen to your body and learn to recognize warning signs. Early warning
signs may be similar to that of dehydration, including nausea, muscle cramps,
disorientation, slurred speech, confusion and inappropriate behavior. Focus
on both fluid and electrolyte replacement.
Article first appeared in Wingfoot Magazine May 2005.
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