Physical Causes of Anxiety, Depression, and Brain Fog
Why a feeling deserves a real look before it becomes a fixed identity
By: Joy Stephenson-Laws, JD, Founder
There is a common order to how most of us handle a low mood, a fog that will not lift, or a heart that races for no reason we can name. We reach for a label first. We call it anxiety, or depression, or burnout, or "something wrong with me." Often that label is accurate and useful. Sometimes it arrives too early.
A clinically important subset of symptoms that feel psychological are driven or worsened by physical processes that are measurable and, in some cases, treatable. Thyroid trouble, nutrient gaps, sleep disorders, medication effects, inflammation, anemia, and blood sugar swings can all speak in the language of the mind. This does not explain most depression or anxiety, and it does not make emotional suffering any less real. It means that before the mind is handed the whole bill, the body deserves to be asked what it is doing.
That is not a detour around how someone feels. It is a way of taking the feeling seriously. At pH Labs we keep coming back to one idea: the feeling is the entry point, not the failure. A symptom is information, and the work is to honor it rather than to be ashamed of it or to wave it away.
There is a simple way to hold this, and it is the same practice we teach everywhere else. Feel, Pause, Act. Feel the thing without rushing to judge it. Pause before you lock it into a story about who you are. Act by getting curious about what your body might be doing. The sections below are really just that middle step made concrete, a set of physical questions worth raising before "this is just how I am now" becomes the final word.
One note before we go further. Some symptoms should not wait for any of this. A new racing or irregular heartbeat, chest pain, fainting, severe shortness of breath, or sudden confusion or weakness needs prompt medical attention, not a careful workup next month. And if you ever find yourself having thoughts of harming yourself, that is an emergency too. In the US you can call or text 988 at any time to reach the Suicide and Crisis Lifeline.
With that said, here are the physical drivers most worth knowing about.
The thyroid: a metabolic dial that also turns mood
The thyroid is a small gland in your neck that sets the pace of metabolism in nearly every tissue, and the brain runs on that pace too. When thyroid hormone drops, brain processes slow along with everything else. People describe it as heaviness, blankness, loss of drive, and trouble holding a thought. Those are also core features of depression, which is why the two get mistaken for each other.
The overlap is not a coincidence of symptoms. Thyroid hormone shapes mood through several routes at once. It influences the body's stress-hormone system (what researchers call the HPA axis), affects the birth of new neurons in the brain's memory centers, interacts with the same mood chemicals that antidepressants act on, and tunes inflammatory signaling. A 2024 review of acquired hypothyroidism laid these out directly.
Here is the careful version of the clinical picture, because this is where the topic gets oversold. Hypothyroidism and depression overlap, and an underactive thyroid is linked to a higher chance of depressive symptoms. But the relationship is not simple, and mild thyroid abnormalities do not explain most depression. The useful takeaway is narrow: for new, persistent, or unexplained mood changes, anxiety, fatigue, or brain fog, especially alongside other thyroid clues like cold intolerance, weight change, or dry skin, a TSH blood test is a reasonable thing to raise. It is not a reason for everyone who feels stressed to demand a thyroid panel.
B12: when a deficiency speaks in the language of the mind
Vitamin B12 does two jobs that matter here. It helps maintain the protective coating around your nerves, and it feeds a chemical cycle the body uses to build the messengers involved in mood, memory, and focus. (For the curious: B12 keeps a process called one-carbon metabolism running, which produces the body's main "methyl donor," the raw material for making neurotransmitters. When B12 is low, that production stalls and metabolic markers such as homocysteine and methylmalonic acid can rise.) You do not need the biochemistry to use the point. When B12 runs low, the symptoms can look surprisingly psychiatric: low mood, anxiety, poor concentration, memory trouble, and in serious cases confusion mistaken for early dementia, along with numbness, balance problems, or nerve pain.
One detail is worth holding onto. These symptoms can appear before the classic anemia of B12 deficiency shows up, and sometimes without it, so a normal blood count does not always rule it out. For borderline cases, clinicians may check homocysteine or methylmalonic acid, though those need context too, since kidney function and other factors can nudge them.
And the necessary brake, because this is where wellness marketing runs wild. The story above is about genuine deficiency. Topping up B12 when your levels are already healthy is unlikely to be the missing piece for mood or focus, and trials in well-nourished people bear that out. The honest move is testing, not blanket supplementation, especially if you carry risk factors like older age, a plant-heavy diet, or long-term use of metformin or acid-reducing medicines, all of which can increase the risk of low B12.
Medications and other things that manufacture anxiety
Some of the most common drivers of new anxiety are sitting in plain sight, and not only in the prescription bottles. A large group of substances pushes the body's fight-or-flight system into overdrive: decongestants like pseudoephedrine, asthma inhalers like albuterol, thyroid medication dosed too high, certain ADHD stimulants, and heavy caffeine. They raise adrenaline-type signaling, the body responds with a pounding heart, jitteriness, and a tight chest, and the brain reads those signals and builds the feeling of fear to match. The anxiety is real. It simply started as a chemical instruction to the body rather than a worry that needs talking through.
Two other patterns matter. Steroids like prednisone act on the brain's stress signaling and frequently cause anxiety or agitation. And stopping certain things abruptly can trigger a surge of its own, because the nervous system had quietly ramped up to counterbalance them. The unifying clue is timing. If a new wave of anxiety arrived close to a new medication, a dose change, a new supplement, more caffeine, alcohol, or cannabis, or something you stopped, that connection is worth raising. One safety point, though: do not abruptly stop a prescription on your own, especially benzodiazepines, antidepressants, steroids, seizure medicines, or alcohol if you drink heavily, since sudden withdrawal from some of these is genuinely dangerous. Notice the timing and bring it to a clinician or pharmacist.
The inflammation route, and a word of caution about mold
There is a real and well-mapped pathway from the immune system to mood. When the body mounts an inflammatory response, it releases signaling molecules called cytokines, and these shift brain function into a pattern researchers call sickness behavior: the dullness, low mood, withdrawal, and fatigue of a bad flu. The same machinery is thought to feed depression in some people, which is why chronic inflammatory conditions so often travel with low mood. This part is not in serious dispute.
That established pathway is also where a popular and much shakier claim attaches itself. Damp, water-damaged buildings can grow mold, and some molds make toxins. The idea that ordinary indoor mold exposure causes anxiety, brain fog, and cognitive decline through inflammation is biologically plausible at the mechanistic level, but not well proven at typical household exposure levels. Mold clearly causes allergic and respiratory problems, so a damp home is worth fixing on those grounds alone. But the broader syndrome marketed online as "mold illness," often under the label CIRS, is not accepted by mainstream allergy and immunology bodies, and its diagnostic criteria and treatments remain under-validated. If you feel unwell in a damp building, fix the building and look for measurable signs of allergy or inflammation. Be wary of anyone selling an expensive branded protocol built on a diagnosis the wider field does not recognize.
A few more worth knowing
Several other physical states wear psychological masks, and all of them are checkable.
Sleep apnea, where breathing repeatedly stops at night, is worth asking about if you wake unrefreshed no matter how long you slept, get morning headaches, snore or wake gasping, feel sleepy through the day, or have blood pressure that is hard to control. It is also underdiagnosed in women, who tend to show up with fatigue, insomnia, and low mood rather than the loud-snoring picture most people imagine, so it gets filed under stress or menopause and missed.
Iron deficiency can show up as fatigue, weakness, low mood, or brain fog, sometimes before anemia is obvious. And blood sugar swings, especially in people on diabetes medication or going long stretches without eating, can produce shakiness, sweating, palpitations, irritability, and a wave of panic that mimics an anxiety attack.
The point is sequence, not substitution
It would be a serious misreading to take all of this as "mental illness is really just physical, so skip the psychology." That is not what the evidence supports. Most depression and anxiety are not explained by a lab value, conditions like bipolar disorder and schizophrenia have deep biological roots that no nutrient corrects, and loss, stress, isolation, and trauma cause real suffering on their own. The point is not to swap one reductive story for another. It is to check the body before a feeling hardens into a fixed identity, because some of the answers are often simple to test for and to treat, and the cost of skipping that step is a person carrying a diagnosis and a quiet sense of personal failure when what they had was a correctable gap.
Start with timing
This is where the pause becomes practical. Before you settle on any explanation, ask when the symptom began and what changed in the weeks or months before it appeared: sleep, diet, stress, a new medication or supplement, alcohol, caffeine, an illness, weight change, menstrual or menopausal status, or a new home or workplace. Patterns do not diagnose anything by themselves, but they tell a clinician where to look, and they often surface a physical trigger you would otherwise have explained away.
Questions worth bringing to a clinician
If you are dealing with new or persistent low mood, anxiety, or mental fog, these are reasonable to raise:
Could my thyroid be involved? A TSH test is a standard starting point.
Should my B12 be checked, and if it is borderline, should homocysteine or methylmalonic acid be looked at too?
Could any of my medications, supplements, caffeine, or alcohol, or a recent change to them, be contributing?
Could a sleep problem like apnea be part of this, even if I don't know whether I snore?
Are iron levels or blood sugar worth checking, given my symptoms?
The goal is not to self-diagnose or to trade mental health care for a lab panel. It is to make sure the body has been asked before the mind is handed the whole bill.
None of this is about distrusting how you feel. It is the opposite. Feel the symptom and let it be real. Pause before you decide it is simply who you are now. Act by getting curious about what your body might be doing. More often than many people realize, what people experience as "something wrong with me" turns out to be the body doing something explainable, and often fixable. Asking what it is doing is not a way of dismissing the feeling. It is a way of taking the whole person, body and mind together, seriously, which is the only way any of us was ever meant to be taken.
(Joy Stephenson-Laws, JD, is the founder and president of Proactive Health Labs (pH Labs), a national nonprofit dedicated to holistic health education. A healthcare attorney for over 40 years and a certified holistic life coach, she is the author of several books on health and wellbeing, including Your Labs Are Fine. You're Not. Her work centers on a single idea: that the feeling is the entry point, not the failure).
Sources & Resources
The thyroid
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U.S. Preventive Services Task Force. "Thyroid Dysfunction: Screening." https://www.uspreventiveservicestaskforce.org/uspstf/recommendation/thyroid-dysfunction-screening
Vitamin B12
National Institute for Health and Care Excellence. "Vitamin B12 deficiency in over 16s: diagnosis and management" (NG239). 2024. https://www.nice.org.uk/guidance/ng239/chapter/recommendations
National Institutes of Health, Office of Dietary Supplements. "Vitamin B12: Health Professional Fact Sheet." https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/
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Medications and substances
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MedlinePlus. "Levothyroxine." https://medlineplus.gov/druginfo/meds/a682461.html
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U.S. Food and Drug Administration. "FDA requiring Boxed Warning updated to improve safe use of benzodiazepine drug class." 2020. https://www.fda.gov/media/142368/download
Inflammation and mold
Dantzer R, O'Connor JC, Freund GG, Johnson RW, Kelley KW. "From inflammation to sickness and depression: when the immune system subjugates the brain." Nature Reviews Neuroscience. 2008;9(1):46-56. https://www.nature.com/articles/nrn2297
Centers for Disease Control and Prevention / NIOSH. "Mold: Health Problems." https://www.cdc.gov/niosh/mold/health-problems/index.html
American Academy of Allergy, Asthma & Immunology. "Toxic Mold Syndrome: Separating Fact from Fiction." https://www.aaaai.org/tools-for-the-public/conditions-library/allergies/toxic-mold
UCLA Health. "CIRS not considered an established medical diagnosis." 2025. https://www.uclahealth.org/news/article/cirs-not-considered-established-medical-diagnosis
Sleep apnea
National Heart, Lung, and Blood Institute. "Sleep Apnea and Women." https://www.nhlbi.nih.gov/health/sleep-apnea/women
Moscucci F, Bucciarelli V, Gallina S, et al. "Obstructive sleep apnea syndrome (OSAS) in women: A forgotten cardiovascular risk factor." Maturitas. 2025;193:108170. https://www.sciencedirect.com/science/article/pii/S0378512224002652
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Iron
Latimer K, Baci G, Layne M. "Iron Deficiency Anemia: Evaluation and Management." American Family Physician. 2025;112(5):538-545. https://www.aafp.org/pubs/afp/issues/2025/1100/iron-deficiency-anemia.html
Mayo Clinic. "Iron deficiency anemia: Symptoms and causes." https://www.mayoclinic.org/diseases-conditions/iron-deficiency-anemia/symptoms-causes/syc-20355034
Fiani D, Chahine S, Zaboube M, Solmi M, Powers JM, Calarge C. "Psychiatric and cognitive outcomes of iron supplementation in non-anemic children, adolescents, and menstruating adults: A meta-analysis and systematic review." Neuroscience & Biobehavioral Reviews. 2025;178:106372. https://www.sciencedirect.com/science/article/abs/pii/S0149763425003732
Blood sugar
Mayo Clinic. "Hypoglycemia: Symptoms and causes." https://www.mayoclinic.org/diseases-conditions/hypoglycemia/symptoms-causes/syc-20373685
(This article is for general education and is not medical advice. It is meant to help you ask better questions, not to replace evaluation by a qualified clinician).
