Unmedicated women with depression do not tolerate heat as well as those on SSRIs

UNIVERSITY PARK, Pa. — Media stories, social media posts and the United States Centers for Disease Control and Prevention have asserted that selective serotonin reuptake inhibitors (SSRIs) — a class of medication commonly used to treat mental health conditions including depression and anxiety — may increase people's vulnerability to heat, leading to concerns that people who take SSRIs are at increased risk for heat-related illnesses in hot weather. A new study by researchers in the Penn State Department of Kinesiology, however, demonstrated that women with clinical depression who take an SSRI may be better able to withstand extreme heat compared to those who do not treat their depression with medication.

“The human body primarily cools itself in two ways — by sweating and by increasing blood flow to the skin so that heat can be released to the environment,” said Kathleen “Kat” Fisher, first author of the study who earned her doctorate in kinesiology from Penn State in May. “This study showed that depression interferes with how women’s bodies regulate their temperatures in the heat. Fortunately, SSRIs seem to largely restore the body’s ability to respond to increases in internal temperature.”

In a recent publication in the Journal of Applied Physiology, the research team compared the physiological responses of women without depression to those of women diagnosed with depression, and those who were treated with various classes of antidepressants. When participants’ body temperatures rose, women with unmedicated depression were slower to begin sweating, slower to begin pumping additional blood to the skin and less efficient at pumping blood to the skin, compared to women without depression and women taking an SSRI to manage their depression.

Depression affects about 10% of the U.S. population and is twice as common among women, the researchers said. SSRIs — including sertraline and fluoxetine — and serotonin and norepinephrine reuptake inhibitors (SNRIs) — including duloxetine and venlafaxine — are commonly the first medications that physicians prescribe, along with counseling, to treat depression.

According to the research literature, depression disrupts the body’s ability to regulate temperature. For instance, Penn State kinesiology researchers previously found that in women with depression, blood vessels dilate less effectively — an important step in pumping blood to the skin and cooling the body — but those taking SSRIs displayed improved blood vessel dilation, similar to people without depression.

The current study assessed whether improved blood-vessel dilation also occurred during heat stress. The researchers recruited 64 women, almost all of whom were in their 20s — 16 with no depression diagnosis, 16 with a depression diagnosis who were not taking medication, 16 with a depression diagnosis taking an SSRI and 16 with a depression diagnosis taking an SNRI.

The women swallowed a small capsule that transmitted their internal body temperature throughout the experiment. Then, participants wore a suit outfitted with tubing that allowed the researchers to pump heated water through it. After 10 minutes of acclimation to 91 degrees Fahrenheit (F) water, the temperature of the water pumped through the suit was increased to 125 F, and participants’ internal body temperatures were continuously measured. The experiment concluded when an individual’s internal temperature increased by 1.8 F, which occurred after 45 minutes on average.

Throughout the experiment, the researchers also measured skin temperature on the arm, calf, chest and thigh; heart rate; blood pressure; blood flow to the skin; and sweating.

“The water pumped into the suit was 125 F, causing skin temperature to rise to about 100 F,” said W. Larry Kenney, professor of physiology and kinesiology, Marie Underhill Noll Chair in Human Performance and Fisher’s graduate adviser and co-author on this study. “As the skin continued to be heated to temperatures similar to sitting in a hot tub, the women’s internal temperature continued to rise.”

Results showed that women with unmedicated depression were slower to start sweating and slower to increase blood flow to the skin. Additionally, when their blood flow to the skin did increase, it did so less efficiently than in women without depression. Despite the later onset of sweating, unmedicated women with depression did not sweat less than women without depression overall.

Women taking SSRIs responded to heat in a similar manner to women without depression, whereas results for women taking SNRIs were similar to unmedicated women with depression. Thus, while SSRIs normalized the responses to heat stress in depressed women, SNRIs did not.

No blood pressure differences were detected among any of the groups.

“Up until now, there has been very little data on how depression or any of these classes of antidepressive drugs affect people’s responses to heat stress,” Fisher said. “This study took the first step toward understanding how women with depression, whether taking medications or not, may respond to extreme heat.”

Kenney said these results challenged common beliefs about SSRIs contributing to heat vulnerability.

“In prior studies, my collaborators and I have identified how several factors — especially age, sex, and activity level — contribute to risk from extreme heat,” Kenney said. “Additionally, there has been widespread concern that many medications contribute to heat vulnerability, but the research evidence behind the risks of many medicines is often thin or nonexistent. Both physicians and people taking SSRIs should be aware that these medications do not seem to contribute to heat vulnerability. Rather, SSRIs improve heat tolerance in depression.”

Other Penn State researchers who contributed to this research include Olivia Leach, postdoctoral scholar in kinesiology, and Lacy Alexander, professor of kinesiology.

Jody Greaney, assistant professor of health behavior and nutrition sciences at the University of Delaware, also contributed to this research.

The National Institutes of Health’s National Institute on Aging helped fund this research through a research grant to Kenney and training grant funding to Fisher.

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