As the U.S. and Canada enter into a heat wave, I get a lot of questions about how heat impacts human behavior and our moods. So three years ago, I wrote a blog entry that reviews the research about weather affects our moods and behavior. It’s still a good overview of the research in this area and worth the read.

But it’s nice to highlight a few points from that article, as well as other research, that demonstrates how the weather — and especially hot weather, in this case — can impact our mood. Does a heat wave lead to more violence? Do we have more or less energy during high humidity? What about depression and anxiety?

Read on for the answers.

Heat waves come and go nearly every year in some part of the world. What makes them especially difficult for indigenous populations during the summertime is that the farther away you are from the equator, the less experience you have with dealing with hot weather. So a slew of 100o F days in Houston, Texas is generally no big deal. But string a few of them together in Vancouver and suddenly it’s an issue.

A few of the findings from the research stand out:

  • Heat waves are related to more violent behavior and aggression
  • Heat waves may be associated with higher drug and alcohol abuse
  • Anxiety tends to decrease with a rise in temperatures
  • Depression and lowered mood tends to increase with a rise in temperatures
  • High levels of humidity — which often accompany a heat wave — lower concentration
  • High humidity also increases sleepiness (probably related to poor sleep)
  • High humidity also appears related to a lack of vigor and energy

If you see a pattern in the above list, you’re not alone. If high temperatures are accompanied by high humidity (as they often are in a summertime heat wave), people have more trouble sleeping (Okamoto-Mizuno, et al. 2005; keeping in mind, not everyone has an air conditioner). Less sleep or a poorer quality sleep over a number of consecutive days causes all sorts of problems in life — including lower concentration, less energy, and even a depressed mood.

The AP also points out that there are greater concerns for older people in hot weather too:

There are changes in an older person that raise the risk for heat stroke and other problems. An older body contains far less water than a younger one. Older brains can’t sense temperature changes as well, and they don’t recognize thirst as easily. […]

Heat exhaustion can cause muscle cramps, low blood pressure, rapid pulse and nausea. It can be treated at home, by drinking water, getting into an air-conditioned room or sitting in front of a fan and misting the body with cool water.

Also, we need to keep in mind that the medication you take may also negatively affect your body’s ability to cope with higher temperatures:

Medicines many older people take also may make them more vulnerable to the heat. These include diuretics for high blood pressure, which increase urination – and make it more important to drink plenty of water, Dale said.

Some types of drugs can interfere with sweating and raise body temperature, including some medicines for insomnia, nausea, prostate conditions, Parkinson’s disease and even Benadryl. Many list “dry mouth” as a side effect – a tip-off to drink more water, Zich said.

Just because the heat didn’t used to bother you when you were young doesn’t mean you should ignore your body’s warning signs when it’s getting more and more dehydrated in hot temperatures.

What You Can Do in a Heat Wave to Help

So given all this, what can you do to minimize the negative side effects of a heat wave?

  • Minimize the time outside in hot temperatures. Put off running any errands or trips outside the house that can wait until the heat wave breaks.
  • If you don’t have air conditioning, seek out friends or family who do. Remember you can spend a lot of time in quasi-public places, like a Walmart or other stores, the local shopping mall, library, senior center, or similar kinds of places that offer air conditioning.
  • If no air conditioner, minimize your indoor temperatures by keeping your blinds or curtains mostly shut, especially southern-facing windows.
  • If you can’t afford an air conditioner, make sure you at least have one or two fans, and drink plenty of water. If you normally drink 2 or 3 glasses of water a day, try to get up to 8 or 12 glasses. Staying hydrated is the most important thing you can do.
  • Talk to your doctor about the dehydrating effects of your medications.
  • Look at the lifestyle of people who live closer to the equator and consider taking a mid-afternoon siesta or nap to help get through the hottest portion of the day.
  • Avoid making any big life changes during a heat wave, especially anything that might be emotional or especially challenging in your life.
  • If you’re a loner, a heat wave is the ideal time to make new friends who have air conditioning.
  • If you’re feeling dizzy or odd, call 911 or emergency services right away.

Heat waves are a normal part of life in most parts of the world. You don’t have to worry about them too much as long as you’re sensible, take things especially easy, and don’t make any big plans for things to do or change in your life. Stay out of the sun and in the shade, and stay indoors in air conditioning as much as possible to limit the negative effects of the heat wave on your own mood and behavior.