Dear Doctor: My siblings and I are very frustrated that we can't get our grandparents to pay attention to those "excessive heat" warnings that get issued during a heat wave. Can you help? They don't take information coming from us grandkids seriously, but I bet they'd listen to actual doctors.

Dear Reader: You've raised an important -- and timely -- issue and we're happy to help you out. You are right to be concerned because the dangers inherent in hot weather are very real, and the potential consequences can be severe. Between 2015 and 2016, the number of people who died as the result of extreme heat more than doubled from 45 to 94. Just this year, 54 people died during a heat wave in Quebec, many of them over 65.

Here in the United States, excessive heat is generally defined as two or more days in which temperatures exceed 90 degrees, often with correspondingly high humidity. While excessive heat poses a grave health threat to all of us, it is particularly dangerous for the elderly. It's also a threat to the very young, those living in urban centers who are isolated and don't have ready access to air conditioning, and individuals doing physical labor or exercising outdoors. People living with certain diseases, such as cardiovascular and respiratory illnesses, are also at elevated risk.

When we can't stay sufficiently cool, our core temperature will rise. The result is a range of heat-related illnesses. Heat exhaustion is characterized by muscle cramping, headache, fatigue, nausea or vomiting, rapid heart rate, and dizziness or fainting. More serious is heat stroke, in which the core body temperature rises to 103 degrees or more. At this point, the body no longer sweats. Instead, the skin will be hot, red and dry. In addition to the symptoms of heat exhaustion, people with heat stroke will experience confusion and even unconsciousness. These extremes in body temperatures can lead to brain and organ damage. In severe cases, multiple organ failure leads to death.

During an extreme heat warning, you should:

-- Seek out air conditioning. If you have it at home, turn it on. If not, find an air-conditioned public space like a shopping mall, public library, community center or a city-run cooling center.

-- Avoid any strenuous activity.

-- Dress in light and loose clothing.

-- Stay hydrated, preferably with water.

-- If you have any vulnerable family members, friends or neighbors, check in on them.

-- Never ever (EVER) leave people or pets in a parked car for any period of time during an extreme heat event, even in the shade or with the windows open.

With heat waves becoming more frequent and severe, it's wise to plan ahead. Know the locations of public spaces with air conditioning. Use drapes or shades to cover windows. Store plenty of bottled water and drink it. A cool bath or shower can help maintain body temperature. And if someone you know exhibits the symptoms of heat stroke, it's a medical emergency. Call 911, then use whatever means available to cool them down until help arrives.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: How does someone know they're dehydrated? I'm worried because my husband swears he drinks "tons" of water, but as best I can tell, he doesn't have more than a glass or so per day, even when it's really hot. He's very active and he's always got headaches, which he blames on air quality, and he's often tired. How can I persuade him to drink more water?

Dear Reader: Hydration can be a tricky thing. Unlike hunger, which triggers physical signals that are pretty robust, the signs of thirst can be more subtle and easier to ignore. However, drinking enough water is crucial to both physical and mental well-being. The adult human body is made up of 60 percent water. It's the main component of our cells and tissues; it's the environment that makes the various transport systems within our bodies possible, and it plays an essential role in the various chemical and electrical processes that keep us alive and healthy. That means we have to continuously replace the water we lose each day through sweat, urination, breath and in various other physiological processes.

We replenish the water our bodies use through the foods we eat and the fluids we drink. According to the National Academy of Sciences, total water consumption for women should be 91 ounces daily, and for men the number is 125 ounces. Depending on your diet, up to 20 percent of that water will come from foods like fruits, vegetables and liquid dairy products like milk, kefir and yogurt. The balance of the deficit has to be made up through beverages. When it comes to hydration, not all beverages are created equal. Although sodas and fruit juices do provide water, they also deliver a hefty dose of sugar. Coffee, tea and other caffeinated beverages can have a mild diuretic effect. And sports beverages, while marketed to replenish the sodium, potassium and magnesium we lose through sweat, are pretty high in sugar as well.

We can't know for sure the cause of your husband's headaches and fatigue. However, both of those, along with dizziness, loss of appetite, constipation, heat intolerance and blood pressure fluctuations are symptoms of dehydration.

Studies show that we also pay a cognitive price for dehydration. Researchers at the Georgia Institute of Technology found that losing as little as 2 percent of your body weight in fluids -- that's 2 pounds per every 100 pounds that you weigh -- led to impaired decision-making and a lack of mental focus. Not only did motor coordination take a hit when study participants became even mildly dehydrated, they also began to flub mental tasks like reading maps, doing arithmetic in their heads and proofreading. The more dehydrated participants became, the more their performance deteriorated.

In your husband's defense, dehydration can be difficult to discern. It's a somewhat crude measurement, but keeping an eye on urine color can help him to track what's going on. A very dark gold equals dehydration. We hope that learning about the physical and mental toll of skimping on water will persuade your husband to take hydration more seriously.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: What's the deal with this new bug that made a bunch of people who ate raw vegetables get really sick? So much for trying to eat healthy!

Dear Reader: You're referring to an outbreak of cyclospora, an infection by a one-cell parasite that causes watery (and sometimes explosive) diarrhea. It enters the body when you eat food or drink water that has been contaminated with stool from someone who has been infected with the parasite.

At the time that we're writing this, there have been two distinct outbreaks of cyclospora this summer. In the first, 237 people in Minnesota, Iowa, Wisconsin and Michigan fell ill. According to the Centers for Disease Control and Prevention, that outbreak was traced to Del Monte Fresh Produce vegetable trays, which contained carrot and celery sticks, broccoli and cauliflower florets, plus a dill-flavored dip. Which component (or components) of the trays was contaminated by cyclospora is not yet known. A second outbreak in Texas, which sickened 56 people, has been also been reported. Health officials are working to track down the source of that outbreak and are also investigating whether the two outbreaks are linked in any way.

The infection, known as cyclosporiasis, can last anywhere from a few days to several weeks. In people whose immune systems have been weakened either by disease, such as HIV/AIDS, or through medical treatment, such as chemotherapy, the infection can last for several months. In addition to diarrhea, which can be quite severe, the infected individual can experience loss of appetite, abdominal cramps, gas or bloating, nausea or vomiting, as well as flulike symptoms such as fever, body aches and fatigue. Symptoms begin to arise anywhere from two to 11 days after the parasite has been ingested.

Because diarrhea has many possible causes, diagnosis of cyclosporiasis can be a challenge. Even in cases when a physician suspects that a parasitic infection may be the cause of a patient's symptoms, he or she must specifically request that cyclospora be included in the laboratory testing of stool samples. According to the CDC, repeated tests may be needed. That's because cyclospora is infectious only at a specific moment in its life cycle, when it produces something known as oocysts. Those may be shed intermittently and at such low levels that they can easily be missed.

A mild case of cyclosporiasis will clear up by itself. In these cases, it's sufficient to address the fluid loss that diarrhea causes by adequate hydration. However, when symptoms persist beyond a few days, it's important to seek medical help. Be prepared to tell your physician about any recent travel to tropical regions where cyclospora is common and any potentially contaminated foods you may have eaten.

A combination antibiotic known as trimethoprim-sulfamethoxazole (Bactrim, Septra) is commonly prescribed for more severe infections. Ciprofloxacin or nitazoxanide (Alinia) may be used as alternatives. You can track the latest information regarding these outbreaks at cdc.gov/parasites/cyclosporiasis/outbreaks/2018/a-062018/index.html.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)