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Cortisol Stress Response is Associated with Iron Status in Pregnancy

This longitudinal study of 168 pregnant Black women reveals that higher cortisol reactivity is associated with lower ferritin levels in the third trimester, while higher basal cortisol predicts increased ferritin via IL-6-mediated inflammation, suggesting that maternal stress physiology significantly influences iron status during pregnancy.

Original authors: Reid, B. M., Celestin, G. F., Georgieff, M. K., Mbayiwa, K., Keenan, K.

Published 2026-06-24

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CC BY 4.0

Original authors: Reid, B. M., Celestin, G. F., Georgieff, M. K., Mbayiwa, K., Keenan, K.

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ⚕️ This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer

The Big Picture: Stress, Iron, and Pregnancy

Imagine your body during pregnancy is like a construction site building a new house (the baby). To build this house, you need a massive amount of raw materials, specifically iron. Iron is the "steel beams" needed to build the baby's blood and brain.

Usually, the body is very good at managing these supplies. However, this study looked at what happens when the construction site manager (the mother's body) is under stress. The researchers wanted to know: Does stress mess up the supply chain of iron?

The Main Discovery: The "Stress Alarm" and the Iron Tank

The researchers studied 168 pregnant women in Chicago. They measured two things:

Iron Levels: They checked the "Iron Tank" (measured by a protein called ferritin).
Stress Response: They put the women through a mild, controlled social stress test (like giving a speech to a judging panel) and measured their cortisol (the body's "stress alarm" hormone).

The Finding:
The study found a specific link, but only in the third trimester (the final stretch of pregnancy).

Women who had a stronger "stress alarm" reaction (a big spike in cortisol during the test) had lower iron levels in their tanks by the end of pregnancy.
It's as if the women whose bodies screamed "Danger!" the loudest during the test ended up with the emptiest iron tanks when the baby was ready to be born.

Interestingly, this didn't happen in the first or second trimesters. The connection only showed up when the baby's demand for iron was at its absolute highest.

How Did They Figure This Out? (The Mechanism)

The researchers wanted to know why stress was draining the iron tank. They looked at two possible "plumbing" issues:

Inflammation (The Fire): They checked for IL-6 and CRP, which are like smoke alarms for inflammation in the body.
The Results:
- The "Fire" (IL-6): They found that women with higher baseline stress (a generally high stress level throughout pregnancy) had a faster-rising "smoke alarm" (IL-6). High IL-6 is known to trick the body into hiding its iron (a defense mechanism), which makes the iron tank look emptier.
- The "Smoke" (CRP): The other smoke alarm (CRP) didn't seem to play a role in this specific story.
- The Stress Reaction: Surprisingly, the big spike in stress (cortisol reactivity) that caused low iron in the third trimester was not caused by inflammation. The study suggests that while inflammation plays a role in general stress, the specific link between a stress reaction and low iron in late pregnancy might be a different, more direct process that the researchers couldn't fully see with the tools they used.

Why Does This Matter? (The "Why")

The paper suggests two main reasons why this happens in the third trimester:

The "Empty Tank" Theory: Pregnancy uses up iron reserves like a car burning through gas. By the third trimester, the tank is naturally low. If your body is also screaming "Stress!" at the same time, it might drain the remaining fuel even faster.
The "Broken Alarm" Theory: Normally, as pregnancy goes on, the body gets better at ignoring stress to protect the baby (the stress alarm should get quieter). But for some women, the alarm stays loud. This "atypical" stress response in late pregnancy might be the extra push that depletes the iron.

What the Study Did NOT Say

To be clear about the limits of this research:

It's not a diagnosis: The study didn't prove that stress causes iron deficiency in every case, only that they are linked in this specific group.
It's not about diet: The study didn't measure exactly what these women ate, so we don't know if stress made them eat less iron.
It's not a treatment plan yet: The paper does not say that taking stress-relief pills will fix iron levels. It simply identifies stress physiology as a new piece of the puzzle.

The Bottom Line

This study is the first to look at how the body's immediate reaction to stress affects iron levels throughout an entire pregnancy. It found that for women in the final months of pregnancy, a strong stress response is linked to lower iron stores. This suggests that a mother's stress physiology is a hidden factor that could contribute to iron deficiency, which is crucial because the baby needs that iron most right at the end of pregnancy to build its brain and blood.

Technical Summary: Cortisol Stress Response is Associated with Iron Status in Pregnancy

Problem Statement
Iron deficiency (ID) affects an estimated 30–40% of pregnant women globally, leading to adverse maternal health outcomes and long-term neurocognitive deficits in offspring. While ID is often attributed to dietary inadequacy, it persists even in supplemented, high-resource populations. There is a known overlap between populations at high risk for ID (e.g., those facing socioeconomic stress) and those experiencing elevated stress, yet the biological mechanisms linking maternal stress physiology to iron status during pregnancy remain poorly understood. Specifically, no prior study had directly examined the association between cortisol (measured at rest and in response to stress) and maternal iron status across the gestational period.

Methodology
This prospective longitudinal study utilized data from the Nutrition and Pregnancy Study (NAPS), a double-blind randomized controlled trial involving 168 pregnant Black women living in Chicago, IL, who were receiving Medicaid. Participants underwent up to four laboratory assessments across pregnancy (visits 1–4).

Stress Physiology: Salivary cortisol was measured using the Trier Social Stress Test (TSST). Indices included basal cortisol (20 minutes post-arrival) and cortisol reactivity (difference between basal levels and peak response at 20 minutes post-TSST).
Iron Status: Serum ferritin was quantified via ELISA. To account for inflammation, ferritin concentrations were adjusted using the Biomarkers Reflecting Inflammation and Nutritional Determinants of Anemia (BRINDA) method, utilizing internal CRP deciles.
Inflammation: Serum Interleukin-6 (IL-6) and C-reactive protein (CRP) were measured to test mediation pathways.
Analysis: Trimester-specific regression models examined the relationship between cortisol reactivity and ferritin. Linear mixed-effects models with moderated mediation tested whether basal cortisol predicted ferritin via inflammatory markers (IL-6 and CRP) across gestation.

Key Results

Cortisol Reactivity and Ferritin: Higher cortisol reactivity to the TSST was significantly associated with lower serum ferritin specifically in the third trimester ( $\beta = -0.197, p = .004$ ). This association was not observed in the first or second trimesters and remained significant after controlling for maternal age, time of day, concurrent self-reported stress (PSS), and BMI.
Basal Cortisol and Inflammation: Higher basal cortisol predicted a steeper rise in IL-6 across gestation ( $p = .002$ ). IL-6 was positively associated with ferritin ( $p = .006$ ), consistent with inflammatory iron sequestration.
Mediation: A statistically significant indirect effect was found where basal cortisol influenced ferritin via IL-6. This indirect effect shifted across gestation, becoming positive in the later stages (28–38 weeks).
CRP Pathway: No significant associations were found between cortisol (basal or reactive) and CRP, nor between CRP and ferritin; thus, CRP did not mediate the relationship.
Temporal Precedence: Analyses of participants with multiple third-trimester visits indicated that earlier ferritin did not predict later cortisol reactivity, nor did earlier reactivity significantly predict later ferritin, though the effect direction for the latter was consistent with the primary findings.

Significance and Claims
The authors claim this is the first prospective study to link cortisol reactivity to iron status across human pregnancy. The primary significance lies in identifying maternal stress physiology as a novel upstream contributor to iron deficiency in late pregnancy.

The paper proposes two non-mutually exclusive interpretations for the trimester-specific finding:

Cumulative Depletion: The impact of stress physiology on iron metabolism may only become detectable once maternal iron reserves are sufficiently depleted by the high demands of the third trimester.
HPA Dysregulation: The persistence of robust cortisol reactivity in the third trimester may be atypical (as reactivity normally attenuates), suggesting a failure of HPA adaptation that, superimposed on physiological vulnerability, suppresses iron absorption or mobilization.

The study concludes that screening for indicators of HPA dysregulation alongside standard iron assessments could help identify pregnant women at elevated risk for iron deficiency. Furthermore, stress-reduction interventions are suggested as a potential complementary strategy to supplementation for preventing gestational iron deficiency and its downstream consequences for infant neurodevelopment. The authors explicitly note that while they did not measure hepcidin, the observed patterns are consistent with an HPA-immune axis involving IL-6 and hepcidin upregulation, warranting future investigation.