What Causes Postpartum Anxiety? The Physiology We’re Not Looking At 

Anxiety is experienced in the brain. That doesn't mean the entire story begins there. 

There is something that has bothered me for a long time about the way we approach postpartum mental health. We have gotten much better at recognizing postpartum anxiety, screening for it, and talking openly about what women are experiencing. This is incredibly important, especially as maternal mental health continues to worsen and more women are finally getting the recognition and support they deserve. 

But there’s a massive piece of this conversation we are still missing. 

When a postpartum woman tells us her heart is racing, she can't sleep even when she's exhausted, can't concentrate, her stomach is in knots, and she feels constantly on edge, we recognize those symptoms as anxiety.  

But what exactly have we explained by calling it anxiety? We've described what she's experiencing. We haven't necessarily explained why she's experiencing it. 

The brain isn't going through postpartum by itself. The entire body is. Thyroid function can shift. Iron stores may be depleted. Immune and inflammatory signaling are changing. Sleep is profoundly disrupted. Nutritional demands remain high. The gut is communicating with the immune and nervous systems. And the reproductive hormone environment has just undergone one of the most dramatic transitions it will experience in a woman's lifetime. 

Every one of those things has the potential to influence what is happening in the brain. 

Yet this is a conversation I see missing from so much of our postpartum mental health training. Once symptoms have been identified as psychological, we have a tendency to stay there. We talk about therapy, medication, trauma, coping, stress, relationships, and support, all of which can be incredibly important, without always asking what is happening physiologically inside the woman experiencing them. 

I don't think those should be separate conversations. And I certainly don't think giving a symptom a psychiatric name should be the point where we stop asking questions about the body. 

Can Iron Deficiency Cause Postpartum Anxiety Symptoms? 

Start with the nutrient that has the most direct postpartum evidence behind it, not evidence borrowed from the general population and extrapolated onto new mothers. 

A prospective trial followed mothers from 10 weeks to 9 months postpartum and found a strong association between iron status and anxiety, stress, depression, and cognitive performance. Iron-deficient anemic mothers who received iron treatment improved on depression and stress measures by 25%, along with measurable gains in cognitive testing, while anemic mothers given placebo did not improve (Beard et al., 2005). 

Iron deficiency can produce fatigue, weakness, dizziness, shortness of breath, a racing or pounding heart, and difficulty concentrating (Milman, 2011). Read that list again.  How many postpartum women would describe that experience as anxiety? 

And this leaves us with an important question. When a postpartum woman says her heart is racing and she’s constantly worried, is that anxiety interpreting a physiological signal, or a physiological signal producing something that gets labeled anxiety? The honest answer is that we can't always tell from the outside, and iron deficiency deserves a place in that differential rather than an assumption that the mind is the only place to look.

Postpartum Thyroiditis and Anxiety 

Narrow the lens to the postpartum population, and the pattern holds. 

Postpartum thyroiditis affects somewhere between 5-10% of postpartum women, with a mean prevalence commonly cited around 7-7.5% depending on the population studied (StatPearls, 2025). It typically runs through two phases. The thyrotoxic phase shows up first, usually within the first few months after delivery, and is associated with anxiety, insomnia, palpitations, irritability, fatigue, and heat intolerance. The hypothyroid phase follows months later and looks almost like a mirror image: fatigue, low mood, constipation, cold intolerance, and poor exercise tolerance (American Thyroid Association). 

The American Thyroid Association notes directly that because these symptoms so closely resemble the ordinary exhaustion and stress of new motherhood, the thyrotoxic phase of postpartum thyroiditis is frequently overlooked entirely. 

A woman going through it isn't imagining her anxiety, and she isn't wrong to call it that. Part of what she's experiencing may genuinely be thyroid physiology producing a hyperthyroid-adjacent symptom picture that looks, to her and to nearly everyone around her, like ordinary postpartum stress. That doesn't mean postpartum thyroiditis causes postpartum depression or anxiety as a general rule. Current evidence doesn't support that broad a claim. It does mean that ruling out thyroid function is a reasonable, evidence-backed step before assuming a symptom picture is purely psychological in origin. 

But even this is too simple, because now we've made iron deficiency and thyroid dysfunction into two separate possible causes of anxiety. That's not really how postpartum physiology works either. 

Inflammation and Postpartum Anxiety: It's Complicated 

Take inflammation. 

We don’t have the evidence to say that postpartum inflammation causes postpartum anxiety. A 2025 systematic review looking at inflammatory cytokines and postpartum depressive symptoms found exactly what I would expect from such a complicated system: some signals, particularly around IL-1β, but inconsistent findings overall (Kurniati et al., 2025). 

But that doesn't make inflammation irrelevant. Inflammatory signaling changes what is happening throughout the body. One of the clearest examples is iron. Inflammation increases hepcidin, which regulates iron absorption and how iron is mobilized from storage. In other words, inflammation can change iron availability. Now our "inflammation problem" and our "iron problem" are no longer two completely separate things. 

Inflammation can also interact with thyroid hormone metabolism and signaling, the HPA axis, gastrointestinal function, mitochondrial function, and neurotransmitter metabolism. And all of those systems have their own relationships with the brain. 

This is where trying to identify one physiological cause of postpartum anxiety starts to fall apart. It may not be inflammation → anxiety. It‘s inflammation altering iron availability, thyroid function, gut function, sleep, or any number of other processes that ultimately change the physiological environment in which that woman's brain is functioning (and good luck capturing that entire sequence with one lab panel taken six months postpartum). 

Nutrition and Postpartum Anxiety: The Brain Doesn't Operate Alone 

And this brings us back to nutrition. 

I wrote recently about how frustratingly inconsistent the research on individual nutrients and postpartum mental health can be. That hasn't changed.  A systematic review of 24 studies and more than 14,000 participants found that 14 of those studies linked perinatal depression to lower levels of folate, vitamin D, iron, selenium, zinc, or fatty acids, while 8 found no association at all (Sparling et al., 2017). A more recent postpartum-specific review found vitamin D carried the strongest signal, with 9 of 13 studies identifying a significant relationship between low vitamin D and postpartum depression symptoms, while lower B12 and zinc also showed associations and the evidence for iron, folate, magnesium, and selenium remained inconsistent (Voros et al., 2025). 

These nutrients aren't simply fuel. They're involved in neurotransmitter synthesis, mitochondrial energy production, one-carbon metabolism, cell membrane structure, antioxidant defense, and myelination, the insulating process that lets neurons fire efficiently in the first place. The postpartum brain doesn't operate independently of the nutritional state of the body supporting it. 

The Gut-Brain Axis and Postpartum Anxiety 

The gut-brain axis gets flattened online into a single claim, that the gut makes serotonin so gut health equals mood health. The actual postpartum-specific research is more interesting than that, and considerably more cautious. 

A 2025 review specifically on the perinatal microbiota-gut-brain axis identified GABAergic signaling, oxytocin, and immunomodulation as key pathways involved in the body's adaptation to pregnancy and postpartum, pathways that are also shaped by intestinal microbes and already linked to vulnerability for mood disorders (Armbruster & Forsythe, 2025). Separately, a 2025 meta-analysis pooling 12 studies found associations between several microbial groups and postpartum depression risk (Guo & Chen, 2025). 

The gut doesn't need to manufacture a mood-relevant neurotransmitter and ship it to the brain for gut health to matter here. It communicates through immune signaling, microbial metabolites, and neuroendocrine pathways that are still being mapped. And now we're back to inflammation and nutrition again. 

Sleep Deprivation and Postpartum Anxiety 

A 2025 systematic review and meta-analysis examining the impact of sleep on postpartum health outcomes found that sleep interventions were associated with improvements in postpartum depressive symptoms, and that better postpartum sleep quality was linked to lower depression and anxiety symptom severity across the pooled observational evidence (Khan-Afridi et al., 2025). Poor sleep disrupts the same emotional-regulation circuitry that anxiety symptoms run through, which means a sleep-deprived brain isn't just tired. It's working with measurably less capacity to modulate an emotional response before it becomes overwhelming. 

Which means sleep isn't sitting off to the side of everything we've already talked about. Sleep disruption can affect emotional regulation, inflammatory signaling, stress physiology, and glucose regulation. Now we're adding another physiological stressor into the same system we're already trying to untangle.

Hormonal Changes and Postpartum Anxiety 

Pregnancy involves an enormous rise in progesterone, estrogen, and neuroactive steroids. Birth ends that pregnancy almost overnight. Allopregnanolone, a progesterone metabolite and a potent modulator of GABA-A receptors, the same receptors targeted by anti-anxiety medications, rises steadily across pregnancy and then falls sharply after birth, remaining comparatively low for up to six months postpartum (Grötsch & Ehlert, 2024).  

But this isn't only theoretical biology anymore. In 2019, the FDA approved brexanolone, a formulation of allopregnanolone delivered by IV infusion, as the first medication specifically indicated for postpartum depression. In 2023, zuranolone followed as the first oral medication approved for the same indication, also working through the GABA-A receptor system modulated by allopregnanolone. 

That doesn't prove that hormonal withdrawal is the cause of postpartum depression or anxiety. The research itself tells us the relationship is far more complicated than that. 

But it does tell us something incredibly important for this conversation: postpartum mental health is biological enough that we have developed psychiatric medications specifically targeting neuroactive-steroid signaling altered across pregnancy and postpartum (medications with zero long-term safety studies and a host of serious side effects, I'll add).

This Is Why Looking at One System at a Time Doesn't Work 

These are not seven independent pathways sitting beside one another. 

Inflammation changes iron availability through hepcidin, which means the iron deficiency we identified earlier may not simply be an iron problem. The same inflammatory environment can influence thyroid signaling. Gut dysfunction can affect what she's digesting and absorbing while simultaneously interacting with immune signaling. Add months of fragmented sleep and now we're affecting emotional regulation, glucose regulation, stress physiology, and inflammation again. Meanwhile, the brain is adapting to an entirely different reproductive hormone and neurosteroid environment. 

So when a postpartum woman presents with anxiety, fatigue, constipation, palpitations, poor sleep, brain fog, and digestive changes, the question isn't necessarily which one of these systems caused her anxiety. 

It may be: what happened across the system that made this particular woman vulnerable to experiencing anxiety now? 

That's a very different clinical question. And it's one of the reasons postpartum physiology cannot be reduced to a checklist of symptoms, labs, or protocols. This is also a huge part of what I teach inside the Postpartum Nutrition Certification. Not how to memorize which lab goes with which symptom, but how to understand postpartum physiology well enough to see the relationships between them. 

A blood test can give us an incredibly useful snapshot. It can identify anemia. Thyroid dysfunction. A nutrient deficiency. Glucose abnormalities. Inflammatory markers. But it can't show us the entire sequence of events that brought her body to that moment. Finding the abnormal marker and understanding why that marker became abnormal are not the same thing. It can't tell us whether inflammation altered iron availability months before ferritin was checked. Whether digestive dysfunction contributed to nutritional depletion. Whether months of broken sleep amplified inflammatory and metabolic changes. Whether she entered pregnancy already depleted, before postpartum ever began. Or how all of those variables interacted with her individual sensitivity to hormonal change.  

The human body is not a collection of independent lab values. Postpartum is perhaps one of the clearest examples of why treating it that way fails women. 

So What Actually Causes Postpartum Anxiety? 

None of this means postpartum anxiety isn't real, isn't psychological, or doesn't deserve therapy and medication when those are the right tools. It absolutely can be all of those things. 

What it means is that the label "anxiety" describes an experience, not an origin story. A racing heart, a mind that won't quiet, a body that feels perpetually on edge, these can be produced by a thyroid moving through a phase nobody's checking for, an iron status nobody's testing, a sleep debt nobody's treating as clinically relevant, or a hormonal system withdrawing from the largest shift it will ever undergo. Usually it's not one of these acting alone. It's several, layered on top of each other, in a body that just built and delivered another human being. 

We've built a version of postpartum mental health care where a psychiatric label functions almost like a stop sign, the point where the physical workup ends and the psychological one begins. But nothing about the body reads it that way. The immune system talks to the brain. The gut talks to the brain. The thyroid, the iron stores, the hormonal environment, all of it is in constant conversation with the same circuitry that anxiety runs through. 

Maybe the more accurate statement isn't that postpartum anxiety is physical instead of psychological. It's that the line we've drawn between those two categories was never really there to begin with, not inside an actual human body trying to recover from what postpartum asks of it.

Learn More About The Postpartum Nutrition Certification: https://postpartumu.com/certification

References 

• American Thyroid Association. Postpartum thyroiditis. https://www.thyroid.org/postpartum-thyroiditis/ 

• Armbruster, M., & Forsythe, P. (2025). The perinatal microbiota-gut-brain axis: Implications for postpartum depression. Neuroimmunomodulation, 32(1), 67–82. https://doi.org/10.1159/000543691 

• Beard JL, Hendricks MK, Perez EM, Murray-Kolb LE, Berg A, Vernon-Feagans L, Irlam J, Isaacs W, Sive A, Tomlinson M. Maternal iron deficiency anemia affects postpartum emotions and cognition. J Nutr. 2005 Feb;135(2):267-72. doi: 10.1093/jn/135.2.267. PMID: 15671224.  

• Grötsch, M. K., & Ehlert, U. (2024). Allopregnanolone in the peripartum: Correlates, concentrations, and challenges, a systematic review. Psychoneuroendocrinology, 166, 107081. https://doi.org/10.1016/j.psyneuen.2024.107081 

• Khan-Afridi, Zain & Ruchat, Stephanie-May & Jones, Paris & Ali, Muhammad & Matenchuk, Brittany & Leonard, Sierra & Jantz, Andrew & Leek, Kier & Maier, Lauren & Osachoff, Laura & Hayman, Melanie & Forte, Milena & Sivak, Allison & Davenport, Margie. (2025). Impact of sleep on postpartum health outcomes: a systematic review and meta-analysis. British Journal of Sports Medicine. 59. 584-593. 10.1136/bjsports-2024-109604. Kurniati AM, Partan RU, Lestari PM, Liberty IA, Zulkarnain M, Effendy KY, Indra B. Relationship between Inflammatory Cytokine and Depressive Symptoms in Postpartum Women: A Systematic Review. J Mother Child. 2025 Jul 19;29(1):63-70. doi: 10.34763/jmotherandchild.20252901.d-25-00006. PMID: 40682534; PMCID: PMC12278369.  

• Milman N. Postpartum anemia I: definition, prevalence, causes, and consequences. Ann Hematol. 2011 Nov;90(11):1247-53. doi: 10.1007/s00277-011-1279-z. Epub 2011 Jun 28. PMID: 21710167.  

• Sparling, T. M., Nesbitt, R. C., Henschke, N., & Gabrysch, S. (2017). Nutrients and perinatal depression: A systematic review. Journal of Nutritional Science, 6, e61. https://doi.org/10.1017/jns.2017.58 

• Voros C, Sapantzoglou I, Athanasiou D, Mavrogianni D, Bananis K, Athanasiou A, Athanasiou A, Papadimas G, Tsimpoukelis C, Gkirgkinoudis A, et al. Invisible Links: Associations Between Micronutrient Deficiencies and Postpartum Depression—A Systematic Review. Life. 2025; 15(10):1566. https://doi.org/10.3390/life15101566  

• Yan Guo & Wangxiang Chen (2025) Meta-analysis of the association between gut microbiota and postpartum depression, Journal of Psychosomatic Obstetrics & Gynecology, 46:1, 2548567, DOI: 10.1080/0167482X.2025.2548567 

This article is original research synthesis by
Maranda Bower, founder of Postpartum University®.

This research was originally published November, 2025.
You’re welcome to share excerpts or discuss these ideas publicly. When doing so, please credit the original work to Maranda Bower / Postpartum University® and link back to this article when possible.

To cite this article:
Bower M. What Causes Postpartum Anxiety? The Physiology We're Not Looking At. 2026. https://postpartumu.com/research/postpartum-anxiety-physiology-causes/