By Craig Olson, M.D
Originally Published in the IAMC Newsletter, August 2010
In the previous two issues of this newsletter we have discussed how dehydration contributes to rider fatigue and potentiates both hyperthermia and hypothermia, all of which are real risks that need to be managed when adventure riding. Since we are in the hottest portion of the adventure-riding season – July and August – it will be worthwhile to briefly review dehydration and hyponatremia and how to manage these two riding risks.
Dehydration occurs when you lose more fluid than you take in and your body does not have enough water (and other fluids) to carry out its normal functions. We routinely lose water as we: 1) breathe with humidified air leaving the body, 2) sweat to cool the body, and 3) urinate or have a bowel movement to rid the body of waste products. Each day the average adult loses more than 10 cups (close to 2.5 liters) of water through these mechanisms [3]. In Idaho’s dry desert climate insensible water loses from breathing and sweating will be much higher than a region of the country with similar temperatures but much higher humidity. To get an idea of the magnitude of these losses, during a brisk walk, up to 16 ounces of sweat may be produced to allow for body cooling. That is a pound of water lost that needs to be replaced [1]. Similar or greater loses routinely occur while riding a motorcycle. These loses can be potentiated by other health conditions (increasing age, diabetes, congestive heart failure, vomiting or diarrhea) and medications (diuretics, antihypertensive, etc.).
Symptoms of mild dehydration become noticeable after 2% of one’s normal water volume has been lost [2]. Since 75% of our body is water, for the average male (150-160 pounds) that is approximately one liter of fluid loss before symptoms become noticeable. For the average female (120-130 pounds) symptoms become noticeable with even less fluid loss. Mild to moderate dehydration is likely to cause dry, sticky mouth, sleepiness or tiredness (fatigue), thirst, muscle cramps, headache, dizziness, and/or lightheadedness. With severe dehydration symptoms will progress to confusion, generalized weakness, coma, progressive multisystem organ failure, and death if untreated [1-3].
Prevention of dehydration is best accomplished by drinking sufficient water. The greater the water losses through perspiration, obviously, the more water that must be consumed to avoid dehydration. For routine non-stressful riding in which a person is not perspiring to any large degree, drinking when one is thirsty is sufficient to maintain hydration. When the riding becomes more technical and demanding, much more physical energy is expended and insensible water losses from perspiring will be significantly higher. Under these circumstances, especially in hot, dry environments, relying on thirst as an indicator of dehydration is not adequate. It is best to hydrate the day before such a ride and keep drinking lots of water during the ride. The best indicator of adequate hydration is urine output that should be copious and clear, not limited and dark yellow (concentrated).
Hyponatremia resulting from an abnormally low blood level of sodium can result from over hydration secondary to compensating for excessive perspiration. Sodium is an essential electrolyte that helps to regulate water levels in the fluid in and around cells. Normal blood sodium levels are 135-145 milliEquivalents/liter. Up to 2 grams of salt (sodium) can be lost per liter of sweat. If only water is replaced (preventing dehydration), hypopnatremia will result [4].
Early warning symptoms of hypponatremia include nausea, muscle cramps, disorientation, lethargy, fatigue, slurred speech, and confusion. Severe forms of hypponatremia may lead to seizures, coma and death. Since the early symptoms are similar to those of dehydration alone, further treatment of dehydration (taking in additional water) only worsens the severity of the hyponatremia [4-5]. According to a recent study, women appear more prone to hyponatremia than men [6].
Again, prevention of hyponatremia is the best treatment by supplementing the rehydration with a sports drink containing sodium (e.g. Gatorade). Use these sports drinks in moderation (perhaps every other or every third liter or replacement fluid) since many contain sugars and/or caffeine (Red Bull, PowerAde, Gatorade, etc) both of which can contribute to dehydration, especially in individuals with diabetes. Avoid salt tablets since they may lead to hypernatremia that worsens congestive heart failure and hypertension. Another alternative for electrolyte replacement is an electrolyte add-in (e.g. Elete) that can be added to your replacement water [4-7].
Be aware of the effects of dehydration and hyponatremia, particularly during the hot, dry riding season, and take active steps to prevent both before and during your ride. Doing so will make your ride more pleasant while reducing and thus adequately managing these two riding risks.
Some of the important things water does for our bodies are illustrated below courtesy of the Mayo Clinic Foundation [5].
References:
1. Dehydration, by Benjamin C. Wedro, M.D.
http://www.medicinenet.com/dehydration/article.htm
2. Dehydration
http://www..wikipedia.ord/wiki/Dehydration
3. Dehydration
http://www.mayoclinic.com/health/dehydration/DS00561
4. Hypnatremia, by Elizabeth Quinn, Sports Medicine
http://www.sportsmedicine.com/od/hydrationan d fluid/a/Hyponatremia.htm
5. Hyponatremia, Mayo Clinic
http://www.mayoclinic.com/healath/hyponatremi a/DS00974
6. Hyponatremia, Medicine Net.com
http://www.medicinenet.com/hyponatremia/article.htm
7. 12 Tips for Keeping your Cool on a Hot Ride, by Patrick Thomas, Spring 2008, http://www.soundrider.com/archive/tips/12_way s_to_ride_cool.htm