New research supports link between temperature, depression symptom severity.

When you think about symptoms of major depressive disorder (MDD), things like rumination, negative emotions, blunted emotions, insomnia, or restlessness might come to mind. Like most people, you might not think about an increase in core body temperature as a sign of severe depression. Nonetheless, a recent study (Mason et al., 2024) of over 20,000 participants suggests exactly that.

Source: Polina Tankilevitch/ Pexels

Linking Temperature and Depression Symptoms in Everyday Life

The study, published in Scientific Reports, used a combination of self-reported core temperature (taken from standard thermometers) and continuously monitored distal temperature (via an Oura ring) and participant-reported depressive symptoms as part of the “TemPredict” study. The study, initially conducted for early COVID-19 detection (Mason et al., 2022), provided the researchers with a unique opportunity to extend some previous findings that had much smaller and more restricted samples of individuals to a much larger cohort of participants in their everyday lives.

Specifically, the researchers looked at a few different types of body temperature. They related them to the degree of depression in participants, categorizing them into “non-depressed,” “mild,” “moderate,” or “severe” levels of depressive symptoms. Initially, the researchers looked at just the core temperature participants reported. Subsequently, they looked at distal body temperature during the day and at night. Here, distal temperature is the temperature collected from the finger that the Oura ring was on.

People With More Severe Depression Run Hotter

The study’s key results suggested that having a higher body temperature while awake was associated with greater depression symptom severity. The individuals with mild depression were a bit hotter than those without depression, those with moderate depression were hotter than those with mild depression, and individuals with severe depression were considerably hotter than all of the groups. This was the case for both core temperature (thermometer-based) and distal temperature (ring-based). Contrary to some previous studies, they didn’t find that temperature during sleep was associated with more depressive symptoms. However, the authors propose that this might reflect a difference in how temperature was measured.

When we sleep, our core temperature tends to drop, but our distal temperature (particularly skin temperature on our extremities) tends to rise. This is part of our body’s thermoregulation process—heat moves away from our core, to our hands and feet, and releases excess heat through sweating and by the air around us absorbing the heat that radiates off our body. This difference may explain why nighttime temperature didn’t predict depression symptoms particularly well, and why the authors propose that if core temperature were measured during this time, they may well have replicated those previous effects.

Source: Polina Tankilevitch/ Pexels

Why Do People With Depression Have Higher Temperatures?

While these results are consistent with other work showing altered thermoregulation in depression (which also shows up as less sweating in depression!), they can’t identify why this is the case using the current data. The researchers put forth a couple of possibilities, though.

One set of possibilities is that both increased temperature and depression share a common cause or causes. There are a few things that are thought to both increase body temperature and also lead to depression, such as chronic stress, low-grade inflammation (reflecting a modest but sustained immune response), and alterations in brain chemistry. Any of these three, or in fact, all of them, could lead to both depression and temperature changes. When it comes to the immune response, there’s reason to believe that changing the body’s temperature may actually reduce depressive symptoms.

Using Acute Heat Exposure to Reduce Depression

Researchers have shown that heat exposure in the short term (i.e., through sauna lamps, hot yoga, etc.) can improve the body’s thermoregulation response, making it more effective and reducing body temperature over time. Some immune responses are sensitive to changes in temperature. In this case, if the cause of depression is low-grade inflammation, it’s possible that directly changing body temperature can reduce this immune response, thereby reducing depressive symptoms. In addition, there’s also evidence that short-term heat exposure can increase the effectiveness of antidepressant medications.

However, the authors of this study (and others) do point out that not all depressed individuals have the same causes of depression, and therefore, inducing a heat stress response might not work for everyone. Additionally, this does not mean that chronic or sustained exposure to heat stress will be psychologically beneficial. Heat waves increase mental health hospitalizations (Nori-Sarma et al., 2022) and are dangerous to those with existing physical and mental health conditions.

Nonetheless, these results are an exciting step towards identifying potential new treatments for some types of depression, and demonstrate just how tightly linked our body's physical states and our mental states really are!