DON GONYEA, HOST:
Here's something millions of Americans across the Midwest and East probably don't need me to say. It is hot. Such an intense and early heat wave, doctors warn, can be especially dangerous. Alejandra Borunda from NPR's climate desk joins us to explain why. Hi there.
ALEJANDRA BORUNDA, BYLINE: Hi, Don.
GONYEA: What is it about this heat wave that is putting people especially at risk?
BORUNDA: Well, it's the first big heat of the season in the Eastern part of the country. It was nearly 100 degrees the other day in Maine. And that really means that people's bodies just aren't yet ready for heat. There's actually a bunch of research showing that more people end up in the hospital or even die during the year's first heat wave. In a study in Boston, for example, older people were about three times as likely to go to the ER for heat problems during that initial heat wave versus the following one.
GONYEA: So our bodies respond to heat differently in June than they will, say, in August.
BORUNDA: Yeah, it's really interesting, actually. Our bodies adjust to heat exposure in a process called acclimatization, and it usually takes a few weeks of experiencing hot temperatures to get there. Here's how it works. First when it gets hot, our hearts have to work overtime to pump blood away from the core, from our internal organs, in order to protect them. Our hearts send that hot blood toward the skin, and that's actually a lot of work. So people's heart rates go up. The heart has to pump more blood with every beat. Dan Vecellio is a heat expert at George Mason University. It was 90 degrees out when we talked. He says after it's been hot for a bit, and people started acclimatizing...
DAN VECELLIO: We see our heart does a better job at pumping that blood to increase that skin blood flow.
BORUNDA: Each pump gets stronger and more efficient.
VECELLIO: So we're pumping more blood with less strain on our heart as we're more readily exposed to the heat.
BORUNDA: It's honestly quite a lot like getting into shape. And that's not all. How people sweat also changes. Like, it gets less salty.
GONYEA: And so how does less salty sweat help?
BORUNDA: Yeah, it's really interesting, right? It means you hold onto your electrolytes better, and your blood stays properly balanced chemically. And this is actually really cool too. Less salty sweat actually evaporates more easily, and sweat evaporation is the main way that our bodies shed heat. People also start sweating sooner. Here's Vecellio again.
VECELLIO: Before, where it might have had to been 90 degrees outside for our brain to think, oh, I'm getting hot, it's time to start sweating - now it might think at 87 or 88 degrees.
BORUNDA: Our bodies also make more sweat, which helps with the evaporation and therefore cooling.
GONYEA: OK, so here's where people in the East and Midwest right now need to pay close attention. What precautions might they take that can help during this early-season heat?
BORUNDA: Yeah, heat stress can really blindside people, so taking it seriously even when it doesn't sound too risky is really important. I spoke to Ashley McClure, a doctor in the Bay Area in California. She says climate change is changing the flavor of heat season, and it's catching her patients off guard.
ASHLEY MCCLURE: When that starts happening sooner, you know, people aren't really thinking about it in May or June. You know, we often think about those intense heat waves being more July and August.
BORUNDA: That's especially because heat waves now last longer and are hotter. That's a hallmark of climate change. So she says drink lots of water, stay cool, especially at night, and take lots of breaks before you get too hot. Just let your body ease into summer gently.
GONYEA: NPR's Alejandra Borunda, thanks so much.
BORUNDA: Yeah, great to talk.
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