Weekly Blog

June 5

With Memorial Day in the rearview and the official start of Summer on the near horizon, now is when we typically talk about the strain of the season. For clients who receive formal education, this month our team will dive deeper into heat, discussing both tried-and-true topics—like proper energy management, acclimation, and cooling techniques required to stay ahead of fatigue—and far less obvious connections, such as gastric distress associated with heat-induced leaky gut. One intriguing connection that didn't quite make the cut (yet) is the impact of heat on mental health and specifically depressive symptoms. It is an emerging science, but the evidence became much clearer this week. Let's start by framing what we know.

As detailed in this 2025 perspective paper, three prevailing theories attempt to explain depressive illness: The "monoamine theory", which emphasizes changes in brain chemical messengers (neurotransmitters) like serotonin and dopamine; the "neurogenesis theory" which emphasizes structural changes in the brain associated with a lack of new cell production; and finally "the inflammation theory" which suggests that depression is triggered by immune system over-activation and excess pro-inflammatory cytokines. The authors argue that since changes in brain chemistry (theory 1) and our ability to sprout and grow new cells (theory 2) are both consequences, not causes, the most plausible driver is poorly regulated inflammation (theory 3). 

While still just a theory, the idea that an excessive or prolonged immune response drives depressive symptoms is certainly an intriguing one. Such a mechanism would explain cases like this one, which include a close connection between depressive symptoms and flu-like symptoms. It would also explain the connection between a pro-inflammatory diet and depression shown here and why exercise—known to lower whole-body inflammation through muscle activation—is also a potent antidepressant. For example, a Cochrane review published in January of this year rigorously reviewed the latest research and found that exercise was as effective as gold-standard treatments like medication and psychological counseling. However, things became more interesting a few weeks ago when a small but well-designed pilot study showed that treating individuals with an anti-inflammatory typically used for Rheumatoid Arthritis had a strong antidepressant effect, outperforming other approved and widely used medications.

So what does this have to do with heat?

While we can't be 100% sure, simple logic would require that if inflammation drives depression risk and prolonged heat exposure drives inflammation (even when fluids are available, as shown here), then heat exposure should also link with depressive symptoms. At least 1 research team that analyzed data from over 100,000 subjects across 263 cities in China showed this was indeed the case.

This isn't a mind-body connection; once again, the research has shown it's all one thing. Having a plan for when things overheat goes a long way toward ensuring the experience is well-managed and temporary. Let us know if we can help.

Have a great weekend,

Mike E.