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Depression is one of the most common psychiatric conditions in America, affecting 21 million people each year.1<\/span><\/sup>\u00a0While factors such as\u00a0the current state of your gut health<\/a>\u00a0influence your mental state, chronic stress is also a key driver behind depression.<\/p>\n According to a new study published in Nature Communications, long-term stress repeatedly activates the body\u2019s stress-response systems, pushing the immune system into a state of chronic low-grade inflammation. As noted by Stacey Kigar, Ph.D., one of the study authors:<\/p>\n Following the hypothesis above, learning how the immune system works under chronic stress is key to discovering new treatments that can benefit patients experiencing this issue. Note, however, that within this field of study, animal testing is used due to ethical concerns.2<\/span><\/sup>\u00a0That said, the knowledge gleaned from the analysis will still positively impact mental health care.<\/p>\n According to the study, repeated social stress sets off a specific immune reaction that alters behavior. Researchers used a well-established model called chronic social defeat stress, which mimics the emotional toll of repeated social pressure, and tracked what happened in the protective layers around the brain \u2014 the meninges.3<\/span><\/sup><\/p>\n \u2022<\/span>Summary of the findings \u2014<\/strong>\u00a0Chronic stress triggered a surge of neutrophils (the immune system\u2019s first responders) into the brain. The researchers theorized that this rush was not just a bystander effect, but a driver of the depression- and anxiety-like behaviors seen in the test subjects.<\/p>\n The mice in this experiment were healthy before stress exposure, which means the changes seen were a direct result of the stressful environment. The stressed group displayed strong signs of anhedonia (the loss of pleasure), avoiding social contact and even ignoring sexual cues. They were also more anxious, exploring less and staying away from lit areas in behavior tests.<\/p>\n Interestingly, about 30% of the mice were\u00a0resilient<\/a>, showing normal behavior despite exposure to stress, giving researchers a comparison group that helped separate stress-specific immune effects from random variation.<\/p>\n \u2022<\/span>A closer analysis of the findings \u2014<\/strong>\u00a0The researchers found a 5.6-fold increase in blood neutrophils and a 1.3 to 1.7-fold increase in meningeal neutrophils in stressed mice. This was not a random spike \u2014 the more neutrophils a mouse had, the more withdrawn and anxious it became. Mice with the highest levels of these immune cells showed the strongest reduction in social approach behavior and pleasure-seeking.<\/p>\n The effect was not fleeting, too. Meningeal neutrophil levels stayed elevated for at least 24 hours after stress ended and only returned to normal after about a week, whereas blood neutrophil levels normalized much faster. This suggests that the immune footprint caused by stress lingers near the brain even after the stressful situation is over.<\/p>\n \u2022<\/span>Where neutrophils came from and where they went \u2014<\/strong>\u00a0Instead of traveling from distant bone marrow in the limbs, many neutrophils came directly from reservoirs in the skull bone marrow and slipped into the meninges through tiny vascular channels.<\/p>\n In other words, stress triggers a very localized immune response right next to the brain, which suggests why mood and behavior are so sensitive to chronic social pressure. These skull-derived neutrophils were genetically more similar to immature bone marrow neutrophils than to circulating blood neutrophils, meaning they were fresh and primed for action.<\/p>\n \u2022<\/span>Meningeal neutrophils were in a hyperactive state with a strong \u201cinterferon signature\u201d \u2014<\/strong>\u00a0They were responding to Type I interferons, immune messengers known to induce depressive symptoms even in healthy people. These neutrophils had reduced major histocompatibility complex (MHC) II expression, a molecule needed to present antigens to T cells, which means they also disrupt normal immune regulation near the brain.<\/p>\n The researchers even identified that some of these neutrophils were physically larger \u2014 a sign of immaturity and heightened activity \u2014 and nearly tripled in number in the stressed animals compared to controls.<\/p>\n \u2022<\/span>Blocking interferon signaling with an antibody against the interferon-\u03b1\/\u03b2 receptor (IFNAR) reversed many of the stress effects \u2014<\/strong>\u00a0Mice treated with this antibody showed restored pleasure-seeking behavior and fewer meningeal neutrophils.<\/p>\n<\/div>\n Taken altogether, the findings show how the immune system leaves an imprint around the brain that keeps the nervous system in a high-alert state. Understanding this process gives you a clearer picture of why reducing chronic stress or modulating the immune system is key to preventing the spiral into depression.<\/p>\n In a report from the Brain & Behavior Research Foundation, Peter Tarr, Ph.D., explains how stress-related immune activation rewires the brain\u2019s emotional control systems and shifts behavior in ways that mimic depression. Instead of focusing only on hormones like cortisol, the researchers examined how cytokines communicate directly with brain circuits.4<\/span><\/sup><\/p>\n This new angle of research is an important breakthrough because it shows depression is not just \u201cin your head,\u201d but also rooted in immune system overactivation that pushes the brain toward a state of energy conservation and withdrawal.<\/p>\n \u2022<\/span>The findings apply to both healthy individuals under chronic stress and those already struggling with mood disorders \u2014<\/strong>\u00a0Elevated cytokine levels were linked with a drop in\u00a0dopamine<\/a>\u00a0(a motivation and reward neurochemical), which explains why stressed people lose interest in activities they once enjoyed.<\/p>\n In parallel, stress increased activity in brain regions like the amygdala that amplify fear and anxiety signals, creating a feedback loop where the brain prioritizes threat detection over pleasure or social engagement.<\/p>\n \u2022<\/span>Your immune system rewires your brain activity \u2014<\/strong>\u00a0When the immune system signals danger, the brain reallocates energy away from reward-seeking toward behaviors that favor survival. That means under long-term stress, your brain is rewiring to keep you cautious and withdrawn \u2014 a response that is protective in short bursts but harmful when it drags on for weeks or months.<\/p>\n The result is your brain is more likely to interpret neutral events as threatening and to overreact emotionally, which compounds feelings of hopelessness.<\/p>\n \u2022<\/span>Inflammatory biomarkers rise during stressful periods \u2014<\/strong>\u00a0The findings also highlighted specific cytokines like interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-\u03b1), which spike during chronic stress and are associated with more severe symptoms. These inflammatory molecules not only float around randomly \u2014 they cross into the brain and alter the way neurons fire in regions like the prefrontal cortex, which is responsible for decision-making and emotional regulation.<\/p>\n \u2022<\/span>How stress-induced immune activation disrupts connectivity in the brain\u2019s reward network \u2014<\/strong>\u00a0Affected areas include the ventral striatum and nucleus accumbens. Functional magnetic resonance imaging (MRI) scans showed that people with high inflammation had lower activation in these regions when shown positive stimuli, like happy faces or rewarding cues. This blunted reward response is what makes normal activities feel joyless and effortful, a hallmark of clinical depression.<\/p>\n<\/div>\n The research shows that feeling unmotivated or emotionally flat under stress is not a character flaw, but a biological process driven by immune signals. Understanding this will help change the stigma and points toward practical interventions, including reducing chronic stress exposure and exploring anti-inflammatory strategies that restore healthy brain signaling.<\/p>\n In another study published in Psychoneuroendocrinology, researchers explored how long-term stress affects the brain\u2019s mitochondria. The researchers used a chronic unpredictable mild stress model in rats, exposing them to a rotating series of stressors over several weeks, such as light\/dark cycle changes, cold swims, and mild restraint. This type of model is designed to replicate the uncertainty and ongoing nature of stress that humans experience.5<\/span><\/sup><\/p>\n \u2022<\/span>The stressed animals developed strong signs of depression-like behavior \u2014<\/strong>\u00a0They stopped drinking sweetened water, which normally indicates pleasure-seeking, and showed longer immobility times in behavioral tests that measure resignation or despair. Brain tissue from these rats showed significant reductions in mitochondrial function, meaning their brain cells were producing far less adenosine triphosphate (ATP) than normal.<\/p>\n At the same time, they had elevated inflammatory biomarkers, with higher levels of cytokines such as IL-1\u03b2 and TNF-\u03b1 in the hippocampus and prefrontal cortex \u2014 two brain regions that are central to memory, emotional regulation, and decision-making.<\/p>\n \u2022<\/span>Several key complexes in the electron transport chain were impaired in the stressed rats \u2014<\/strong>\u00a0Among those affected are Complexes I and IV, which are required for the step-by-step process that extracts energy from food and converts it into usable ATP. When they were disrupted, oxidative stress levels rose sharply, leading to damage in brain cell membranes and proteins.<\/p>\n In other words, the brain\u2019s energy system isn\u2019t only running slower \u2014 it\u2019s also producing more toxic byproducts that further injure neurons.<\/p>\n \u2022<\/span>Treatment with antioxidants or mitochondrial-supporting compounds improved behavior and partially restored mitochondrial function \u2014<\/strong>\u00a0Rats that received these interventions regained interest in sweetened water and showed more active coping behavior in stress tests.<\/p>\n This shows that targeting\u00a0mitochondrial health<\/a>\u00a0could reverse some of the emotional and behavioral effects of chronic stress, which is promising for people who feel stuck in a low-energy, low-motivation state after prolonged stress exposure.<\/p>\n \u2022<\/span>Mitochondrial dysfunction was not immediate \u2014<\/strong>\u00a0It worsened progressively over several weeks of ongoing stress. This means that the longer the stress continues, the more deeply the brain\u2019s energy systems are disrupted, which explains why chronic stress leads to a deeper and more persistent form of depression compared to short-lived stressors.<\/p>\n It also highlights the importance of early intervention \u2014 reducing stress before mitochondrial damage becomes entrenched can prevent long-term mood problems.<\/p>\n \u2022<\/span>The inflammatory response and mitochondrial dysfunction amplified each other \u2014<\/strong>\u00a0The more inflammation was present, the worse the mitochondrial damage became. Moreover, the weaker the mitochondria, additional inflammatory cytokines were produced. This vicious cycle created a loop that locked the brain into a state of low energy and high inflammation, making it harder for the test animals to recover naturally even after the stressors were removed.<\/p>\n \u2022<\/span>Mitochondrial protection is a key therapeutic target for preventing stress-induced depression \u2014<\/strong>\u00a0The researchers noted that supporting mitochondria through proper nutrition, reducing exposure to stressors, and using compounds that protect mitochondrial enzymes could offer a way to stop the downward spiral.<\/p>\n<\/div>\n If you\u2019re feeling down, the answer isn\u2019t taking an antidepressant pill. It\u2019s far better to address the source of your stress before your mood takes a nosedive. Considering this, here are several strategies to manage your stress:<\/p>\n 1.<\/span>Add healthy carbs to your diet \u2014<\/strong>\u00a0Cortisol, commonly called the \u201cstress hormone,\u201d is strongly influenced by what you eat. When your body doesn\u2019t have enough glucose available, it compensates by producing cortisol, which then breaks down muscle, bone, and even brain tissue to create amino acids that your liver converts into glucose.<\/p>\n This means that consistently eating too few healthy carbohydrates can cause cortisol levels to rise just to keep your body running smoothly. That\u2019s why I\u2019m cautious about recommending long-term fasting or extended\u00a0time-restricted eating<\/a>. While these approaches can help with short-term weight loss, they also lead to persistently high cortisol levels over time, which can speed up aging.<\/p>\n Research published in the journal Nutrients found that a carbohydrate-rich diet helped lower cortisol and improved mood after stress.6<\/span><\/sup>\u00a0That said, what\u2019s a good amount to aim for every day? I recommend 250 grams a day from fruits and white rice. Then, gradually add root vegetables, non-starchy vegetables, starchy vegetables (like sweet potatoes and squash), and finally, minimally processed whole grains.<\/p>\n 2.<\/span>Exercise regularly \u2014<\/strong>\u00a0Getting your body moving is one of the most effective tools for managing stress. When you work out, your body releases endorphins \u2014 your natural \u201cfeel good\u201d chemicals \u2014 which boost your mood and act like built-in pain relievers.7<\/span><\/sup><\/p>\n Exercise<\/a>\u00a0also helps keep cortisol in check. By moving regularly, you improve your sleep quality and strengthen your emotional resilience, which makes you better equipped to handle life\u2019s challenges. It also supports long-term health and longevity. By consistently lowering cortisol, you reduce your risk of stress-related conditions and give your body a buffer against chronic tension. If you aren\u2019t exercising, the perfect time to start is now.<\/p>\n I recommend reading \u201cNailing the Sweet Spots for Exercise Volume<\/a>\u201d to give you an idea on how to structure your workout regimen.<\/p>\n
Immune Cells at the Brain\u2019s Border Are Driving Stress<\/strong><\/p>\nStress Signals Hijack Mood Networks in the Brain<\/h4>\n
Stress Weakens the Brain\u2019s Power Plants and Triggers Inflammation<\/h4>\n
Natural Strategies to Address Stress and Protect Your Mental Health<\/h4>\n