St. Louis ? Folks who will suffer heat-related illnesses this sweltering summer seem to have one thing in common.

“They think they can handle it,” said Dr. Mark Levine, an emergency room physician with Barnes-Jewish Hospital in St. Louis. “They’re outside and exercising and take a run around Forest Park and think that they don’t have to stop and get shade, or they don’t want to stop and drink fluids.

“When they get to a point where they’re exhausted, weak, even dizzy, they’re already in trouble. Your body has started to shut down.”

Experts agree that many people overestimate their stamina in the heat and wait for symptoms to occur before attempting to take precautions. By then, it could be too late.

“Heat-related illness is probably the most common preventable injury that we see across the country,” said Dr. Matthew Matava, an orthopedist and associate professor at Washington University School of Medicine.

The real bad guy in the heat conspiracy, Matava says, is dehydration. That occurs when your body has lost too much water and the nutrients that go with it. For inactive people, it’s the result of not drinking enough water.

For active people it’s the result of not drinking enough water while sweating away what water you have.

Infants, children, the elderly and people with illnesses are most susceptible.

Dehydration can be mild to life-threatening. In addition to dry mouth and sunken eyes, you also may have vomiting, diarrhea, dizziness or the feeling that you can’t keep anything down.

Matava, who also is team physician for the Rams, says he sees heat problems especially during training camp, because young players don’t drink enough water.

Jeremy Nutt, who works at Mike's Auto Service in Lawrence, uses a fan to cool off from the 90-degree temperatures. Experts say too many people overestimate their stamina in the heat. Symptoms of overheating include dizziness, weakness, dry mouth and fatigue.

Despite what trainers tell Rams players, “I’ll put in five IVs” in training camp, he says.

During the summer, there’s a lot of sweating. Trainers watch out for professional athletes, but other competitors, especially children and teens, need to be vigilant about preventing dehydration, Matava said.

The symptoms can be quite scary. For example, dizziness occurs when the heart slows because of dehydration. Your brain isn’t getting enough blood, and you’re struggling to stay conscious.

As the condition worsens, the body stops sweating and internal temperature rises. You may cramp, get nauseated and even black out. By then you should be in an emergency room getting fueled from a plastic bag of saline solution.

What frustrates physicians is that it’s so easy to prevent. The key: Drink water regularly, whether you’re thirsty or not. “Your thirst centers are inaccurate,” Matava said.

To be safe, start drinking a few hours before an event.

Matava added, “The ultimate problem is a complete shutdown of the cardiovascular and neurologic function. You’ll have increased sweating and, eventually, your body shuts down and you lose the ability to sweat. You may become unconscious.

“That’s what you see: Someone is passed out, it’s 90 degrees, and he’s not sweating.”

Once the problem gets to that stage, it’s time for medical help, he said. “Often, the body won’t accept water by mouth and intravenous hydration is necessary.”

Extra danger from dehydration occurs among people who can’t look after themselves very well: children, who are too young to care for themselves, and older people, who sometimes won’t take care of themselves.

Babies and children

Babies tend to sweat less and aren’t equipped to handled high heat and sunlight, said Dr. Susan Bayless Mallory, a pediatric dermatologist at St. Louis Children’s Hospital. That changes with age, but parents must make sure children are drinking enough water and not getting too much sun, she said.

Babies and young children often suffer more sunburn than heat problems, she said. That happens because parents let young children play in the sun too long, or they take babies outside in strollers that aren’t shaded.

“A lot of people just don’t think,” Mallory said. Even for teenagers, parents should be vigilant, she said.

“I try to tell teenagers who are really fair not to be lifeguards,” she said. “They sit out all day in the blazing sun. It’s better now because of sunscreens and umbrellas, (but) they have more exposure than they should have.”

Teens also have the added problem of overdoing it, especially in competitive sports. Area hospitals report that most heat-related problems among teens are from athletes who play too much and drink too little.

Elderly

“The elderly are a bit more sensitive to the effects of heat because of physiologic changes as people get older,” said Dr. Julie Gammack, assistant professor of geriatrics at St. Louis University School of Medicine. “The body doesn’t regulate sweating and temperature as well. In fact, we find older adults tend not to get fevers when they get ill. Sometimes they actually get lower temperatures.”

That means it’s often difficult to tell when an older person has become dehydrated.

“The more frail, the more chronic medical conditions a person has, the more medications they’re taking, makes them at higher risk for excess heat,” she said.

In addition, the body doesn’t sweat as much.

“They can’t use that as a way to get rid of excess heat when they get hot,” she said. “Older adults’ skin tends to be drier, (with) not as much perspiration. They may not notice the sweating response to being overly warm as they did when they were younger.”

That’s compounded when people live alone and face the economic problems of balancing expenses for food, medication and comfort. Often, air conditioning is the first thing to go. Then, for fear or some other reason, they shut up the house and it becomes unhealthy.

Also, “There are many diseases of dementia that can cause people to become paranoid or reclusive,” Gammack said. “That certainly can be the case that people are fearful. That’s why they shut their doors and windows.”

In any event, it’s essential that someone check on older people living alone.