The Biochemistry of Sustained Fear: What living under the threat of deportation does to the brain — and why it matters.

Future Substance Use Disorder Treatment

August 24, 2026

Heather Dale, MS, MPA, NTP, CRNCII, Author

Tom O'Connor, Publisher

Somewhere in America this morning, a parent is deciding whether it's safe to take their child to the doctor. A family is sitting at breakfast, calculating the risk of the school run. Someone is not going to their therapy appointment because the fear of being seen outweighs the fear of not getting help. This is not anxiety in the abstract. This is what anxiety looks like when it has a specific, daily, concrete shape — and when it goes on long enough, it stops being just a feeling. It becomes something the brain carries in its structure.

That's what I want to talk about. Not politics. Not the policy. The biology of what sustained fear actually does inside the brain.

Sustained Fear: What Chronic Threat Does Inside the Brain

I'm a functional nutritionist and addiction recovery specialist. The work I do is built around one premise: that the brain is a physical organ, and when it has been under sustained assault — from substances, from trauma, from chronic stress — it needs more than insight and coping skills to heal. It requires the biological conditions that enable healing. You cannot think your way out of a depleted nervous system.

What's happening right now in immigrant communities is, in that sense, a story I recognize. And I think it's one more person who needs to understand — whether you're a practitioner, someone living inside this fear, or a family member watching someone you love struggle to hold it together.

A large national survey conducted in late 2025 found that nearly four in ten immigrant adults had experienced measurable harm to their mental health from immigration-related fears that year. Among those without legal status, that number climbed to 77%. Clinics are reporting rising no-show rates. In Dallas, childhood vaccinations in Hispanic communities dropped by more than half in a single year — not because parents stopped caring, but because they were afraid to walk through the door. Therapists describe clients arriving in states of hypervigilance so constant that it has become their normal.

These numbers describe something real and urgent. But they don't describe what's happening one layer down — inside the brain of a person who has been living this way for months or years. That's the part we need to look at.

The brain has a calming system whose whole job is to bring you back to baseline — to quiet the alarm after a threat passes, to let you sleep, to make an ordinary afternoon feel okay. A key part of that system runs on GABA, a neurotransmitter that essentially tells overactive neurons to stand down. Think of it as the brain's primary off switch for fear.

In a 2010 study published in the American Journal of Psychiatry, researchers used brain imaging to measure GABA activity in the prefrontal cortex of healthy volunteers, then told them they might receive an electric shock. Not that they would — just that they might. Within eight minutes, GABA activity had dropped by nearly a fifth. In healthy brains. From nothing more than the possibility of something bad happening.

Now think about what it means to live inside that kind of uncertainty, not for eight minutes, but for years. The GABA system doesn't just dip — it gets ground down. And when it does, the brain loses its ability to quiet itself after a threat passes. The off switch stops working reliably. The alarm stays on.

Sustained stress also depletes dopamine — the system that drives motivation, follow-through, and the capacity to feel that effort is worth it — and serotonin, which governs mood stability and sleep. These aren't abstract processes. They show up as the exhaustion that won't lift, the sleep that won't come, the sense that nothing is ever going to be okay.

Other research has found that under severe, prolonged stress, the brain can actually lose physical connections — real wiring — in the regions that handle emotional regulation and clear thinking.

Not weakened. Gone.

This isn't a metaphor for feeling overwhelmed. It's a description of how sustained fear affects the brain over time.

There's something else worth understanding. Under high stress, the prefrontal cortex — the thinking, planning part of the brain that can weigh consequences, hold a plan, and make a thoughtful choice — essentially goes quiet.

Cortisol, the stress hormone, suppresses the very circuits you'd need to think your way through a difficult moment.

Something older and more reactive takes over instead. Its only job is to get you through the next ten minutes. I can't see next week. It can't access the plan you made this morning.

This is why a moment of calm can vanish so quickly. Why can someone feel almost normal, and then a siren outside, a news alert, or a knock at the door pull them straight back into high alert? It isn't fragility. It's a brain trained by its circumstances to treat almost anything as a potential threat.

For families living under constant threat, that shift isn't occasional. It becomes the baseline.

And for many people in immigrant communities, this isn't the beginning of the story. It's a new chapter layered on top of years of pre-migration trauma — violence, persecution, dangerous journeys, family separation.

Research has found that adults whose parents were deported during their childhood had more than twice the likelihood of PTSD symptoms years later. A nervous system that has been under strain for a long time before any of this started is now being asked to absorb even more.

There's also a nutritional layer that rarely gets discussed. The brain builds its neurotransmitters — GABA, dopamine, serotonin — from raw materials that must come from food: specific amino acids, vitamins, and minerals. Chronic stress burns through those supplies fast. So does poor sleep and disrupted eating.

Studies of refugee populations consistently find high rates of B vitamin and iron deficiency, both of which directly limit the brain's ability to produce the chemistry it needs to regulate mood and manage stress.

It isn't just that the situation is overwhelming. The brain is also running low on the fuel it needs to function. When someone living under this kind of fear can't seem to do what they want to do — can't sleep, can't focus, can't hold a plan together — this is often part of why.

Not a lack of resilience. A depleted brain.

For practitioners working with these communities, a worn-down nervous system struggles to absorb new information, hold a plan, or access clear thinking when fear arrives.

Biological stabilization — sleep, nutrition, nervous system support — isn't a detour from real work. It is the foundation on which the real work has to sit.

When someone can't seem to function the way they need to, the first question worth asking isn't just what's going on emotionally — it's whether the system has anything left to work with.

For those living this — or loving someone who is: what you're experiencing has a biological explanation. Fear isn't weakness. The exhaustion isn't a sign that you can't handle it. Your brain has been pushed to its limits, and it is responding exactly the way a brain under that kind of pressure responds. That's not a personal failing. It's a physical reality. And physical things can be repaired.

The brain under this kind of sustained fear is not broken. It is responding. Knowing that doesn't make the situation less urgent. It makes it more, because it means this isn't a permanent state. The brain can heal.

Even here. Even now.

References

KFF/New York Times Survey of Immigrants, November 2025. Hasler G, et al. "Effect of Acute Psychological Stress on Prefrontal GABA Concentration Determined by Proton Magnetic Resonance Spectroscopy." American Journal of Psychiatry, 2010.

Sanacora G, et al. "The Stressed Synapse 2.0: Pathophysiological Mechanisms in Stress-Related Neuropsychiatric Disorders." Nature Reviews Neuroscience, 2021.

Pinedo M, Escobar C. "Childhood Parental Deportations, Immigration Enforcement Experiences, and Posttraumatic Stress Disorder Among US-Born Latino Adults." American Journal of Public Health, 2024.

Cuffe K, et al. "Update: Vitamin B12 Deficiency Among Bhutanese Refugees Resettling in the United States." CDC/MMWR, 2014. See also: CDC Immigrant and Refugee Health — Nutrition and Growth Guidelines.

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