- For the world as a whole, 2023 is shaping up to be the hottest year on record as if you couldn't tell something was up.

As a nurse in summer steamy Philadelphia, I can tell you extreme heat is not healthy.

You know that sluggish where you get on a hot and humid day?

That's just the start.

(enlightening music) Since 2018, the number of deaths due to heat waves has risen sharply around the world.

Experts say the real number is hard to pin down, but every year extreme heat kills somewhere between 1,300 and 20,000 people in North America alone.

And guys, before researching this, I had no clue.

That's a big range.

That's because it depends on what you count as death caused by heat.

- In the medical community, the numbers we have for heat-related deaths is likely a vast underestimate.

Heat is called the silent killer for a reason, because you have to have such high degree of suspicion in order to recognize these patients who frequently have multiple things going on.

- Even the CDC says that heat related cause of death is often misdiagnosed.

That's because there are so many possible symptoms.

- They might be having stroke-like symptoms, heart symptoms, as well as infections, pneumonias, urine infections, viral syndromes, as well as organ dysfunction.

- The biggest danger comes during an extended stretch of high heat and humidity, like the heat wave that hit the Pacific Northwest in 2021 when temperatures hit 121 Fahrenheit and killed more than 800 people, or the Chicago heat wave in 1995 where more than 700 people died.

European countries reported 62,000 heat deaths in the summer of 2022, their hottest on record up to now.

In 2010, a heat wave caused an estimated 55,000 deaths just in Russia.

And in 2003, a blast of heat and humidity across Europe killed as many as 70,000 people.

Some places have it worse than others.

In the United States, our problem children, California, Texas, and Arizona have just 23% of the population but account for 43% of heat-related deaths.

So how do you get to the point of literally dying from heat?

- What I see are a lot of people with underlying medical conditions, heat wave comes through, and then it makes their underlying heart failure worse.

Frequently what we see is actually a peak several days after the kind of hottest part of the heat wave duration, because people have been enduring these stressors, and then all of a sudden, it catches up to them.

- We humans normally have a constant body temperature, just over 98 degrees for most people.

There's a structure in your brain that works like a thermostat to keep it steady.

It's called the hypothalamus.

When it's time to cool things down, it sends electrical signals to the sweat glands, because you guessed it, sweat is how the body cools off.

Sweat glands brings salt and water to the surface of the skin where it evaporates.

This works as a cooling method because the evaporation process needs energy.

And it gets it in the form of body heat.

In fact, water is about 25 times more efficient than air at conducting heat.

Of course, if it's just too hot for too long a time, it can overwhelm your body's ability to sweat it all away.

That's when you get heat exhaustion or heat stroke.

Heat exhaustion is caused by excessive loss of water and salt.

Symptoms include nausea, dizziness, weakness, and more.

- The big one that I see, especially in our older adults with an aging US population, is dizziness.

I had one older individual.

And she was outside mulching just for a couple of hours.

She did this pretty routinely, but the heat index was very high.

And the air quality index was also high.

And so she ended up coming in just really unsteady because she couldn't even walk to the bathroom by herself without falling.

- It is most likely to affect people who are older or with high blood pressure.

This usually requires medical attention.

But in the early stages, you can just cool the person off and rehydrate.

And as far as rehydration, would you say that water is just as good as the sports drinks, or which one is better?

- For moderate activity, usually less than two hours or so, water is great.

Once you get more strenuous activity going on several hours, electrolyte replacements are really quite beneficial, whereby those electrolytes and all the salts in your blood can be replaced.

- Now there's a difference between heat exhaustion and heat stroke, which is even more serious.

- It is life-threatening.

It is essentially two things.

One, hypothermia, or temperature is usually 104 degrees Fahrenheit or higher, or 40 degrees Celsius and higher, mixed with central nervous system dysfunction.

Our patients that we see are confused.

Some of them have seizures, or even in a coma, and completely reliant on multiple forms of life support.

We need to cool the entire human body as fast as we can, ideally within 30 minutes.

- Heat stroke is a critical emergency, but it's not the only way that extreme heat is dangerous.

Over time, heat takes a toll on all the systems in your body.

Your pulse goes up.

It puts more stress on the heart.

It's kind of like a stress test.

- It makes these patients' hearts beat much faster.

They can beat faster for a little while, but then they're not gonna be able to compensate, especially because they're weaker than normal.

- The lungs, too.

Hot weather makes air pollution worse.

It dehydrates you and it raises ozone levels, which makes it harder to breathe, especially for people who already have asthma or chronic lung disease.

- Heat makes the lungs wetter, inflamed, and angry.

And that's mixed with, again, poor air quality, which often has toxins in place as well.

And your lungs just do not like that.

- And the kidneys take a beating, too.

They're not exempt here.

Dehydration leads to lower blood volume, which makes the kidneys work harder struggling to filter the blood.

That can lead to a buildup of toxins, which can mean long-term damage.

- But I think of it as kind of clogging up your kidneys.

And it can cause kidney failure, and even death.

- In a similar way, chronic overheating can also lead to liver problems.

And this whole situation is not getting better anytime soon.

Globally, 2023 may still end up as the hottest year on record.

Now, experts will tell you, if you can avoid the heat, do it.

Stay inside when the sun is blazing and it's 100 degrees outside.

Obviously, but some people, well, they just can't help themselves.

Pam Reed is an ultramarathon runner.

And when we say ultra, we mean ultra.

In fact, she just finished doing three races of 100-miles-plus, each and all within the last three weeks, including the Badwater, 135-mile-run starting in Death Valley, the hottest place on earth.

Pam, the question is, why?

(laughs) Why?

- It's really who I am.

It's my lifestyle.

Running is my life.

I do it for my mental stability and for, you know, physical.

And it's just something, it's like brushing my teeth.

- So the one that was in Badwater was the one that was the hottest.

How hot is hot?

How hot did it get?

- So I've done Badwater since 2002.

And back then, it was in the middle of the day.

It started at 6:00, 8:00, and 10:00 AM.

And now because the park service doesn't really allow them to put an event on during the day, we have to start at night.

Obviously, that's a little cooler, right, because it's in the dark.

So it was about 107, I think, at night.

- You've had races in 2002, 2003, where the temperatures hit 128 degrees Fahrenheit.

- Yes, yes.

- How was that?

- That is crazy.

You know, we would turn a corner, and the wind would stop.

And it felt like the temperature rate went up like 15 degrees, you know?

And my legs were just boiling so hot.

And so, you know, they have sprayers.

They sprayed me down.

And that's how I kept going.

You have a cotton T-shirt on and they're spraying you down.

So the wind cools you down.

- Evaporation, just like sweat.

And what are some other strategies to stay cool?

Like, is there certain things that you wear?

What are some other strategies?

- Yeah, the other strategy would be arm sleeves.

They're cooling sleeves.

You put them on your arms, and then you can, A, just wet them down, or, B, you can put ice in them.

So that's really good.

The other thing I use is a sock, like a men's nylon sock.

I put ice in it and I wrap it around my neck.

And that is amazing, because, you know, it gets your carotid arteries, and it's really definitely cooling.

- Normal core body temperature is around 98 degrees Fahrenheit, but running in the heat on average will bring that up to between 101 and 103 degrees Fahrenheit.

Remember, once you hit 104, you're at risk for heat stroke.

Oh my goodness, Pam, I don't know, something about this is, so your heat tolerance is unusual.

You've been studied, right?

You did a test?

- They did this study at the University of Arizona.

They put a rectal thermometer.

And I was on a bike.

And it was 100 degrees and 100% humidity.

I just rode, and I don't know, I mean maybe a half-an-hour, hour.

And then they were watching my temperature.

And it really didn't go up hardly at all.

- So have you always been comfortable in high-heat temperatures?

- I grew up in the Upper Peninsula of Michigan where it was freezing cold, but you know what, I'm Finnish.

I'm half Finnish.

So I also grew up taking saunas all the time.

I moved to Arizona when I was 19.

And I went to college there and I got married.

And I definitely have acclimated to the heat.

And, you know, the more you're out in it, the more you introduce that heat to yourself, and you just, I'm out in it all the time.

You know, I don't use air conditioning in my car.

I just get used to having the heat.

I like it.

- Obviously some people naturally have more heat tolerance than others, but it's not fixed.

You can train your body to adapt to different temperatures and be more efficient.

- I would say it goes somewhere for three to five days and just do three days of intense training where you just run one hour at a time.

So you go out an hour, come back in, cool down, go back out another hour, and do that five times, three to five times, and do that for three days.

And I think that will really help you acclimate.

If you have water with you for that hour, make sure you're, you know, do the ice sock or do the arms.

Just take care of yourself.

- So what does it mean for the rest of us that are not ever doing training like this?

Let's say you're not ready for an ultramarathon, but you don't wanna be stuck inside all summer.

- Your body is amazing.

Just thinking about all the different ways we walk and move and do activities, in general it takes one to two weeks to acclimate to these warmer environments.

- And one more thing to keep in mind, many common medications can affect the body's ability to sweat or to regulate its temperature, which puts you at risk of overheating.

Common culprits include blood pressure medications like beta blockers, diuretics, some antidepressants, stimulants for ADHD, like Ritalin or Adderall, and antihistamines.

If you're taking any of these, you want to be more conservative when you're out in the heat.

(enlightening music) - That does it provide us this week.

Stay cool if you can.

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