Harvard Medical School: the link between chronic stress, white blood cells, and cardiovascular health

Editorial Note

This article was previously published and updated to reflect the most robust scientific knowledge and available literature reviews. The text is for informational and educational purposes only: it does not replace the advice of a doctor. Scientific sources are indicated at the bottom with verifiable DOIs.

IN BRIEF

• Experimental studies in mice and observations in people indicate that prolonged psychosocial stress can increase leukocyte production via adrenergic signals from the autonomic nervous system.
• A study from Harvard Medical School showed that chronic stress can activate hematopoietic stem cells and increase neutrophils and monocytes, factors implicated in vascular inflammation. [1]
• Proposed mechanisms include norepinephrine release, interaction with β-adrenergic receptors in the bone marrow, and reduction of CXCL12, a factor that keeps stem cells in their "niche." [1][4]
• The evidence combines preclinical data, translational studies, and observational research: the relationship is biologically plausible but requires interpretive caution. [2][3][5][6]

Abstract: what does science say?

In simple terms: "chronic stress" refers to repeated or prolonged exposure to social, work, or personal events that maintain elevated neuroendocrine activation signals. Experimental research in animal models and observational studies in humans show that this condition can increase the production of certain types of white blood cells (neutrophils and monocytes) and modify the behavior of already circulating blood cells. These changes promote inflammatory processes in arterial walls which, in the presence of other risk factors (cholesterol, hypertension, diabetes), can contribute to the progression of atherosclerosis. Key studies highlight a role for norepinephrine and β-receptors in the bone marrow in mobilizing hematopoietic stem cells. This is not a unique and definitive proof of causality: the studies are at different levels (experimental, translational, and observational) and have methodological limitations that require further research and confirmation in large populations.

The reference study: what did the researchers observe?

A group from Harvard Medical School reported key findings linking prolonged stress to changes in hematopoiesis and pro-inflammatory signals in the arteries. This work combined human data and murine models: in the examined participants, researchers detected increases in certain leukocyte counts during periods associated with greater perceived stress; in mice subjected to chronic stress, increased proliferation of hematopoietic stem cells and an increase in neutrophils and monocytes were observed, with worsening characteristics of atherosclerotic plaques. Experimental data also suggested that norepinephrine released by sympathetic fibers acts on bone marrow components, reducing CXCL12 production and promoting the emigration and production of myeloid cells. The totality of this evidence led the authors to hypothesize a "brain–bone marrow–vessel" circuit that makes the link between chronic stress and vascular inflammatory alterations biologically plausible. [1]

Main clinical and experimental results

The study documented: (1) signs of leukocytosis associated with psychosocial stress in observed individuals; (2) in murine models, activation and proliferation of hematopoietic progenitors; (3) the role of adrenergic signaling and the β3 receptor in the bone marrow; (4) a decrease in some plaque vulnerability characteristics when the β3 pathway was experimentally blocked. These elements support strong biological plausibility, although the direct transition from experimental observation to clinical recommendations is not immediate. [1][4]

Proposed biological mechanisms

The most accredited mechanism integrates the systemic release of catecholamines (particularly norepinephrine) due to sympathetic nervous system activation with local responses in the bone marrow. Sympathetic nerve fibers, with their innervation of the stromal compartment, modulate the production of chemokines like CXCL12 that regulate the quiescence and retention of hematopoietic stem cells; the reduction of CXCL12 facilitates the proliferation and mobilization of myeloid progenitors to the circulation and peripheral tissues. The increased availability of neutrophils and monocytes can increase inflammation in the atherosclerotic plaque, promoting remodeling and potential instability. Complementary evidence shows that similar signals are activated by social stress and that drugs or interventions that block the adrenergic pathway can attenuate the stress-induced hematopoietic response in preclinical models. [1][2][3][4]

Role of bone marrow and microenvironment

The bone marrow is not just a passive reservoir of cells: its stromal cells (including populations identifiable by Nestin expression) produce factors for maintaining stem cells. Interaction with adrenergic terminals regulates these factors, so neuroendocrine alterations can directly remodel hematopoietic activity. This idea is supported by studies that have characterized the medullary "niche" and the dependence of retention signals on adrenergic pathways. [4]

Observational and clinical evidence: how much does stress affect practice?

In the human population, numerous epidemiological studies show associations between psychosocial factors (work, social isolation, financial stress) and overall cardiovascular risk; prospective and case-control studies document relationships between stressful exposures and acute myocardial infarction. In the clinical setting, mental stress-induced ischemia has been associated with a worse prognosis in patients with coronary heart disease, suggesting that acute reactions to stress can have significant consequences in the context of already existing disease. However, the observational nature of these studies alone does not allow for establishing a causal relationship: confounders and concomitant factors (e.g., lifestyle habits, comorbidities, socioeconomic context) require in-depth analysis and, where possible, controlled experimental interventions to evaluate the direct effect of stress reduction on cardiovascular outcomes. [5][6][8]

What it means in practice

For the common person, the practical message is preventive and informative, not prescriptive: prolonged stress is a factor that, along with traditional ones (smoking, hypertension, cholesterol, diabetes, sedentary lifestyle), contributes to creating an inflammatory environment that can accelerate the progression of cardiovascular diseases. Reducing exposure to stressors when possible, improving social and work support, and managing conventional risk factors remain sensible approaches. In healthcare, the results suggest that measures that modulate adrenergic activity or inflammation could, in the future, play a complementary role to conventional therapies, but the use of targeted drugs requires robust and approved clinical evaluations. [7][8]

Reasonable practical actions to consider

Without proposing specific therapies, it is reasonable to consider stress support strategies (access to mental health services, occupational counseling, adequate sleep, regular physical activity, supportive social relationships) integrated with the control of traditional cardiovascular factors. Large-scale interventions that reduce social stress and inequalities can also impact cardiovascular health at the population level. [8]

Key takeaways

• Chronic stress can alter white blood cell production and promote an inflammatory state potentially relevant to atherosclerosis. [1]
• Mechanisms involve adrenergic signals acting on the bone marrow and the supportive microenvironment (e.g., CXCL12). [1][4]
• Animal data and some human data are consistent; however, clinical evidence requires larger studies and targeted interventions to confirm direct causal impacts. [3][5][6]
• Inflammation is a relevant biological target for cardiovascular diseases: anti-inflammatory trials have shown that modulating inflammation can reduce cardiovascular events in selected subgroups. [7]
• Managing stress as part of a comprehensive cardiovascular prevention approach is a prudent strategy, but there are currently no specific pharmacological recommendations based on this mechanism for the general population. [8]

Limitations of the evidence

It is important to distinguish between study types and levels of evidence: experimental animal studies allow for exploring biological mechanisms and testing interventions on molecular pathways; human observational studies show associations but can be influenced by confounders. Many studies on the topic combine different approaches (experimental, translational, observational) to obtain an integrated view, but the transition from mechanistic plausibility to clinical proof of benefit is not automatic. Frequent methodological limitations include reduced sample sizes in some translational studies, subjective or variable measures of "stress level," and the difficulty of isolating the effect of stress from related factors (diet, physical activity, socioeconomic conditions). To advance towards clinical recommendations, large-scale prospective research, targeted randomized interventions, and evaluation of relevant clinical outcomes are needed.

Editorial Conclusion

Research conducted by the group affiliated with Harvard Medical School has made a significant contribution to linking, at a biological level, chronic stress, hematopoiesis, and vascular inflammation. The hypothesis of a nerve–marrow–vessel axis is well supported by experimental data and finds corroboration in translational studies. However, the path from mechanistic plausibility to consolidated preventive or therapeutic strategies for the population is still ongoing. Integrated management of cardiovascular risk factors, including attention to psychosocial stress when present, represents a prudent approach. Healthcare professionals and public decision-makers should consider this evidence in the broader context of cardiovascular prevention and population mental health.

EDITORIAL NOTE

Article updated for scientific and divulgative clarity. The information reported here is intended to inform and not to constitute clinical guidelines. For personal health advice, consult your doctor.

SCIENTIFIC RESEARCH

1. Heidt T, Sager HB, Courties G, et al. Chronic variable stress activates hematopoietic stem cells. Nat Med. 2014;20:754–758. https://doi.org/10.1038/nm.3589
2. Powell ND, Sloan EK, Bailey MT, et al. Social stress up-regulates inflammatory gene expression in the leukocyte transcriptome via β-adrenergic induction of myelopoiesis. Proc Natl Acad Sci U S A. 2013;110:16574–16579. https://doi.org/10.1073/pnas.1310655110
3. McKim DB, Niraula A, Tarr AJ, et al. Social stress mobilizes hematopoietic stem cells to establish persistent splenic myelopoiesis. Cell Rep. 2018;25:2552–2562.e3. https://doi.org/10.1016/j.celrep.2018.10.102
4. Méndez‑Ferrer S, Michurina TV, Ferraro F, et al. Mesenchymal and haematopoietic stem cells form a unique bone marrow niche. Nature. 2010;466:829–834. https://doi.org/10.1038/nature09262
5. Marsland AL, Walsh C, Lockwood K, John‑Henderson N. The effects of acute psychological stress on circulating and stimulated inflammatory markers: a systematic review and meta-analysis. Brain Behav Immun. 2017;64:208–219. https://doi.org/10.1016/j.bbi.2017.01.011
6. Vaccarino V, Almuwaqqat Z, Kim JH, et al. Association of mental stress–induced myocardial ischemia with cardiovascular events in patients with coronary heart disease. JAMA. 2021;326:1818–1828. https://doi.org/10.1001/jama.2021.17649
7. Ridker PM, Everett BM, Thuren T, et al. Antiinflammatory therapy with canakinumab for atherosclerotic disease. N Engl J Med. 2017;377:1119–1131. https://doi.org/10.1056/NEJMoa1707914
8. Janssen H, Koekkoek LL, Swirski FK. Effects of lifestyle factors on leukocytes in cardiovascular health and disease. Nat Rev Cardiol. 2024;21:157–169. https://doi.org/10.1038/s41569-023-00931-w