To Your Health:

Summertime And the Livin' Is Steamy ...

By Nancy DiMarco, Ph.D.

If you’re like many Texans, including myself, Saturdays are days to work outside, take long walks, or bike ride, play sports, go fishin’ … you get the picture. What many folks don’t realize is that they are losing lots of water by breathing hard, from water evaporating off their skin and sweating.

Typically, we replace the fluid we lose rather unconsciously throughout the day from the drinks and foods we normally consume. But unless you are purposeful about replacing that fluid when it is really hot, you run the risk of dehydrating yourself and setting up the more serious problem of heat stress or even heat stroke.

Why is sweating important and why humidity is not your friend?

As the temperature increases, so does you body temperature, even more when you’re working or exercising in the heat. As the body attempts to maintain normal temperature, it begins to sweat.

As air moves over you, evaporation occurs which removes much of the internal heat but also the water along with minerals such as sodium, chloride and potassium. Humidity can prevent this removal of heat from occurring.

You actually sweat more when it is humid, but cooling is not as rapid. Because the air holds so much water, sweat cannot evaporate. It beads up on the skin’s surface, rolls off and carries more water and minerals. This is called futile sweating because body temperature is not decreased.

People have died when the temperature was 75 degrees but the humidity was more than 95 percent. It’s not uncommon for an individual to lose as much as 50-68 ounces of fluid per hour in such conditions.

Also, be aware that antihistamines and some blood pressure drugs diminish sweating and may increase dehydration risk.

What is dehydration?

Dehydration occurs when a person does not take in as much fluid as he is losing through sweat or urination.

Dehydration is considered to be mild if you lose 3 to 5 percent of your body weight. So, for example, a 5-pound loss in a person weighing 100 pounds would be considered a mildly dehydrated state. This may not sound like a lot, but to a competitive athlete, the loss of 5 percent body weight can mean a decrease in performance of 30 percent and a 10 percent decrease in blood volume.

A moderate dehydration is a loss of 6 to 9 percent of body weight. And severe dehydration is a loss of 10 percent or more of your body weight — a life-threatening situation.

What causes dehydration?

Dehydration can develop as a result of low fluid intake, but it also can develop as a result of restrictive clothing in a hot environment, diarrhea or excessive salt intake.

What are some of the symptoms of dehydration?

Some of the symptoms to watch for include a rapid breathing; rapid heart beat; feeling cool or cold even when it is hot outside; hair standing on end (piloerection); higher core and skin temperatures; lack of sweating; headache; nausea; concentrated, dark urine or no urine; muscle cramps; sunken eyes and lack of alertness or confusion.

Can you drink too much water?

Yes! Just like everything else, too much, even of a good thing can be bad. There are more than a few examples of military recruits and marathon runners who have died because of a condition called hyponatremia, or low blood levels of sodium caused by drinking too much water, too quickly without replacing this vital mineral.

It actually can occur in athletes who become dehydrated and lose excessive amounts of sweat, such as during an endurance event like a marathon or all day soccer, tennis, or swim meet. Those who are most at risk are small, slow athletes who sweat a lot and are overly concerned about drinking. A contributing factor to hyponatremia, especially in athletes, is non-steroidal anti-inflammatory drug abuse (aspirin, etc.) that may change kidney function and prevent urine formation.

How much water should you drink?

It’s a really good idea to weigh yourself before and after you exercise or have spent considerable amount of time working outdoors, such as mowing the lawn, trimming, gardening, raking, hoeing, especially in the heat of summer.

Before you exercise, or work outdoors, drink 17 to 20 ounces of water, two to three hours before you begin. Before the start of exercise or work, drink another 7 to 10 ounces, 10-20 minutes before you begin. During exercise or working outdoors, drink 28 to 40 ounces per hour or at least 7 to 10 ounces every 10-15 minutes. After working out, continue to drink at least 20 ounces per pound of weight you lost within two hours.

What about sports drinks for fluid replacement in a heated environment?

If you are exercising for more than an hour in a hot environment, water is probably not enough to replace the minerals you lose through sweat. A sports drink containing both carbohydrate (4 to 8 percent or 7 to 14 g/8 oz) and minerals (28 mg/8 oz) provide electrolytes and stimulate faster rehydration than water alone. Avoid fluid replacement beverages that contain carbonation or caffeine; either one can prevent complete rehydration.

Bottom line?

For most individuals, water is the beverage of choice to prevent dehydration – and forego oxygenated water. It’s another marketing ploy by a few companies to exploit health-conscious people. The water contains more myth than math.

More to come!

Dr. Nancy DiMarco is a research professor in the Department of Nutrition and Food Sciences, the nutrition coordinator for the Institute for Women's Health and coordinator of the master's program in Exercise and Sports Nutrition at Texas Woman's University. She can be reached at ndimarco@twu.edu.

For Further Information Contact:

Roy Kron
Director of News and Information
Tel: (940) 898-3456
e-mail: rkron@twu.edu