Record heat wave in the U.S. raises public health concerns

More than 100 million Americans this week were under some sort of heat advisory, and were warned to stay indoors if possible. From Texas to California, a massive heat wave has set record temperatures, raising concerns about how hot is too hot. W. Larry Kenney, a professor of physiology and kinesiology at Penn State, joins William Brangham for more on how extreme temperatures impact the body.

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  • Amna Nawaz:

    This week, more than 100 million Americans were under some sort of heat advisory and were warned to stay indoors if possible.

    From Texas to California, a massive heat wave has set record temperatures, raising concerns about how hot is too hot.

    William Brangham has our report.

  • William Brangham:

    Amna, Las Vegas, Phoenix, Denver, and St. Louis are among some of the cities that have reported record-setting temperatures this month. And more than 50 million Americans are expected to endure triple-digit temperatures in the days to come.

    And we know these heat waves can be deadly, like this time last year in the Pacific Northwest, where hundreds of people in the U.S. and Canada were estimated to have died from the heat.

    For more on how extreme temperatures impact the body, I'm joined by W. Larry Kenney. He's a professor of physiology and kinesiology at Penn State.

    Larry Kenney, great to have you on the "NewsHour."

    I think most people have some sense of how they personally react when they go outside and they work outside on a really hot day. But can you give us a primer on what you know, what we know about what extreme heat does to the body?

  • W. Larry Kenney, Penn State:

    Thank you for having me on.

    We have been studying the effects of heat stress and dehydration human health and performance for a long period of time. And these recent heat waves that you have mentioned have really brought it into focus for a lot of people.

    Humans really are tropical animals. So we're pretty much geared up physiologically to withstand short periods of high temperatures and humidities. But it's the prolonged exposure to temperature and humidity that's really taken its toll.

    When we are exposed to prolonged high temperatures, there's an increase eventually in our body core temperature, which can, if left unchecked, affect many of the body's systems. But, primarily, it also affects the cardiovascular system, because the heart has to work increasingly hard to pump blood flow to the skin to try to dissipate the heat that we're building up.

    And we're doing that in the context of profuse sweating, which decreases our body fluids and blood volume.

  • William Brangham:

    So what are the sort of worst examples of the things that can happen? What are the sort of illnesses that can come from extreme heat?

  • W. Larry Kenney:

    The two most serious types of heat illness are heat exhaustion, which is primarily a function of high-intensity exercise in a hot environment. And it's really a cardiovascular symptom, cardiovascular consequences that can be treated with moving to the shade, resting, getting body fluids.

    The more severe manifestation of heat illness is heatstroke. And heatstroke is exemplified by two criteria, one, an excessive rise in your body core temperature, over 104 degrees Fahrenheit, and then some sort of cognitive impairment or neurological dysfunction, such as not knowing where you are, how you got there, losing consciousness, and so on.

    And heatstroke is a life-threatening situation that always needs to be treated with exigency.

  • William Brangham:

    And what — we know that these — people who are vulnerable to these kinds of complications, it's not spread equally over the population, right? Certain people are more vulnerable?

  • W. Larry Kenney:


    Our interest has been in the aging population. And in reference to your lead-in, we're doing a series of experiments now looking at that specific question you mentioned, which is, how hot is too hot, how humid is too humid where being over the age of 65 or 80 makes a difference?

    So, even in healthy aging, we have increased vulnerability to heat stress. Then all of the comorbidities that come along with aging, like cardiovascular problems, diabetes, respiratory problems, some of the medications that are taking all add on to that toll.

    The other group that really has a disadvantage when it comes to heat stress are infants, who primarily are at the beck and call of parents to make sure they're — they stay cool, stay well-hydrated, and so on.

  • William Brangham:

    We know that climate change is making these heat waves more common, and the ones that then come are more intense.

    So, human beings are going to have to be living in these extreme circumstances more and more often. You touched on this idea of, how hot is too hot? When do we get to the point where human beings simply can't be living and working outside? What is that? Do we know?

  • W. Larry Kenney:

    I think we have a pretty good idea, especially in humid climates.

    There is an old adage among the meteorology community that that will happen when the ambient temperature gets to about 95 degrees Fahrenheit and 100 percent humidity. But our research, especially some of our recent research, has shown that that occurs actually at lower temperatures, something more on the order of 88 degrees and 100 percent humidity, or 100 degrees and 60 percent humidity, even in healthy young men and women.

    So we have not approached that 95 degree 100 percent humidity extreme anywhere on Earth, for at least prolonged periods. But we're getting very close to the one that we have uncovered.

  • William Brangham:

    And it seems like that's going to then change how we build our cities, how we air condition our homes. I mean, it seems like we're talking about major infrastructural changes if we're going to keep living in this warming world.

  • W. Larry Kenney:


    And a lot of the problems, in addition to or on top of health-related problems, come from disparities in socioeconomic status, access to air conditioning, being able to be looked in on by neighbors and taken to someplace that does have air conditioning if necessary.

    So a lot of these problems are really coming to the head at the present time.

  • William Brangham:

    All right, Larry Kenney of Penn State University, thank you very much for being here.

  • W. Larry Kenney:

    You're very welcome.

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