Three Factors That Affect Depression I Never Knew About — And How Sauna Helps
I always thought depression was about low serotonin, bad sleep, stress, and past trauma. But during my thermalist training with Susanna Søberg, I came across three biological factors I’d never heard linked to mood before: inflammation, IL-6, and BDNF. I thouvght this was interesting because we usually talk about endorphin and dopamine hits as the mental health componant of saunas...and these can be somewhat short lived. However in this article we talk about something that is longer term. I admit this is a bit of a chewy read but if you have had or someone you know has had depression or suicidal thoughts in particular then this is defo worth a read.
Posted on Sun 3 Aug 2025 · by Danny
The Surprising Role of Inflammation, interleukin-6 (IL-6) and BDNF
Let’s unpack how these two interact with sauna use — and what this means for depression, inflammation, and wellbeing.
What Does Inflammation Have to Do With Depression?
Chronic, low-grade inflammation is now recognised as a significant factor in many cases of depression and anxiety. Elevated inflammatory markers like IL-6, TNF-alpha, and CRP have been found in people with major depressive disorder (MDD) [1].
IL-6 in particular is one of the most consistently elevated cytokines in individuals with suicidal ideation, suicide attempts, or a history of severe mood disorders [2,3].
Inflammation interferes with brain function by:
Disrupting serotonin and dopamine metabolism
Lowering BDNF levels
Causing fatigue and cognitive fog
Promoting stress hypersensitivity
IL-6: A Key Immune Molecule with Two Faces
Interleukin-6 (IL-6) is a cytokine — a signalling molecule that plays a role in the body’s immune response. But it’s not all bad news.
In chronic stress, IL-6 acts as a pro-inflammatory agent and is associated with worse mood outcomes [1,2].
However, during acute stress — like exercise or heat exposure — IL-6 is released as an anti-inflammatory signal, triggering downstream healing effects [4].
This dual role makes IL-6 one of the key regulators in whether inflammation harms or helps.
What Happens to IL-6 During Sauna Use?
A 2023 study by Flux et al. [5] found that whole-body hyperthermia (WBH) — akin to a long sauna session — caused a sharp, temporary increase in IL-6 levels in the blood. Interestingly, participants who had the biggest spike in IL-6 after heat exposure also had the greatest improvement in depression scores six weeks later.
This suggests that acute IL-6 increases may be a therapeutic signal, prompting the body to recalibrate its inflammatory pathways and mood regulation systems.
Similar responses are seen after physical exercise, cold-water immersion, and even fasting — all of which elevate IL-6 acutely and have known benefits for mood and brain health.
BDNF: Brain Fertiliser Boosted by Heat
Brain-derived neurotrophic factor (BDNF) is crucial for:
Repairing and regenerating neurons
Supporting learning, memory, and adaptability
Protecting against stress and trauma
Low BDNF levels have been found in individuals with depression and anxiety. Encouragingly, sauna exposure increases BDNF, supporting the brain’s capacity to grow, rewire, and heal [6].
BDNF appears to rise in parallel with IL-6 after heat exposure, particularly when IL-6 is working in its anti-inflammatory mode.
Heat Therapy as a Depression Treatment
In a clinical study involving 30 adults with moderate-to-severe depression, a single session of whole-body heat therapy led to a significant and lasting reduction in depressive symptoms, measured up to six weeks later [7].
This antidepressant effect is thought to stem from the combination of:
IL-6 spikes, leading to downstream release of anti-inflammatory agents like IL-10
Increased BDNF, improving neuroplasticity and stress resilience
Temporary increase in body temperature that mimics fever or physical exertion, activating healing responses
Chronic vs Acute IL-6: Why the Timing Matters
Not all inflammation is equal. It’s important to distinguish between chronic and acute IL-6 elevation:
Chronically high IL-6, caused by ongoing stress, poor sleep, unresolved trauma, or illness, is linked to depression, anxiety, and suicidal thoughts. This kind of background inflammation wears down the brain and immune system over time.
Acutely elevated IL-6, which happens briefly after exercise, a cold swim, or a sauna session, is beneficial. It acts as a signal to the body to start an anti-inflammatory clean-up process. In these cases, IL-6 helps trigger healing, mood elevation, and brain repair.
So it’s not about avoiding IL-6 — it’s about using it wisely. A short blast of heat (like a 15–30 minute sauna) mimics the body’s natural stress response in a way that encourages resilience and recovery, rather than breakdown.
The Bottom Line
Chronic inflammation, driven by stress and modern lifestyles, contributes to depression.
Sauna exposure, when used properly, triggers short-lived IL-6 spikes that help regulate the immune system.
This is followed by an increase in BDNF, which supports emotional resilience and brain health.
Multiple studies now suggest that regular sauna use may help reduce depressive symptoms, especially when part of a broader wellness routine.
While sauna use isn’t a replacement for therapy or medication, it can be a powerful complementary tool in managing mood and supporting mental health.
References
Miller, A.H., Maletic, V., Raison, C.L. (2009). Inflammation and its discontents: the role of cytokines in the pathophysiology of major depression. Biological Psychiatry, 65(9), 732–741.
Brundin, L. et al. (2015). The role of inflammation in suicidal behaviour. Acta Psychiatrica Scandinavica, 132(3), 192–203.
Zhang, H. et al. (2023). Suicide and inflammatory markers: A systematic review. Frontiers in Psychiatry, https://www.frontiersin.org/articles/10.3389/fpsyt.2023.1231031
Pedersen, B.K., Febbraio, M.A. (2008). Muscle as an endocrine organ: IL-6 and other myokines. The Journal of Applied Physiology, 98(4), 1154–1160.
Flux, M. et al. (2023). Whole-body hyperthermia in major depressive disorder: A randomized clinical trial. Translational Psychiatry, https://www.nature.com/articles/s41398-023-02402-9
Naghii, M.R. et al. (2011). The role of BDNF in the pathophysiology of major depressive disorder and implications for treatment. Archives of Clinical Psychiatry, 38(4), 144–149.
Janssen, C.W. et al. (2016). Whole-body hyperthermia for the treatment of major depressive disorder: A randomized clinical trial. JAMA Psychiatry, 73(8), 789–795.