Chronic stress, immune imbalance, and thyroid dysfunction are deeply interconnected. This forms a stress–immune–thyroid triad where each system influences the others, affecting energy, mood, and resilience. Research shows that targeted support—including adaptogens, micronutrients can help restore communication across this network. Rather than offering quick fixes, this systems-based approach addresses underlying feedback loops, combining clinical insight, patient engagement, and supportive lifestyle practices to rebuild physiological balance and improve well-being over time.
Allison Sayre, WHNP
Thyroid Hormone Imbalance and Heart Health
The thyroid is a hormone-producing gland responsible for regulating metabolism. When thyroid function slows down, clinicians see an increase in thyroid stimulating hormone (TSH), a decrease in free thyroid hormones (mainly T4) in circulation, and hormone activity in target tissues starts to suffer. Hypothyroidism is a highly common endocrine disorder affecting about 4.6% of the population in the US, with much higher prevalence in Caucasians, women, and adults over 60. [1]
While there are some infamous symptoms of hypothyroidism, like cold sensitivity and fatigue, one of the more underappreciated relationships is the role of thyroid hormones in heart function and vascular physiology. Alterations in the levels of thyroid hormones impact cardiovascular function, resulting in decreased cardiac output, impaired left ventricular function, and increased vascular resistance. [1] Furthermore, studies have shown a higher prevalence of cardiovascular risk factors (like dysregulated blood pressure or cholesterol) with both subclinical and overt hypothyroidism. [1]
Large-Scale Statistics
A major pooled analysis of over 1.8 million participants revealed that individuals with clinically low thyroid hormone levels were more likely to experience adverse cardiovascular outcomes compared to those with normal, healthy levels of thyroid hormones. [2] This included greater risk of events affecting the blood supply to the heart, higher rates of fatal complications, and increased all-cause mortality.
Even those with only slightly elevated regulatory hormone levels (indicating early dysfunction) faced significantly higher odds of cardiovascular events. [2] These findings indicate that even modest hormonal imbalances may contribute to long-term vascular and cardiac issues.
Why it Happens: Mechanisms Behind the Hormone-Heart Link
Multiple trials and reviews have explored how low levels of thyroid hormones affect cardiovascular physiology. Key mechanisms include:
1. Reduced Cardiac Efficiency
Thyroid hormone deficiency, whether clinical or subclinical in diagnosis, can diminish the heart's ability to pump effectively. This can lead to decreased cardiac output due to impaired relaxation of vascular smooth muscle and a decreased availability of endothelial nitric oxide. [3] This results in less oxygen delivery to tissues, potentially leading to symptoms such as fatigue and exercise intolerance.
2. Increased Resistance in Blood Vessels
A reduction in hormone-driven nitric oxide availability can impair vascular relaxation. [3] The result is elevated resistance within arteries, contributing to increased pressure and workload on the heart.
3. Altered Lipid Profiles
Low hormone activity slows lipid metabolism, which can lead to elevated cholesterol and triglyceride levels. [4] This shift in circulating fats can further impact the elasticity and health of blood vessels. [4]
4. Changes in Coagulation and Inflammation
Low hormonal output may also be associated with increased clotting factors and systemic imbalance in cytokine response, both of which can affect cardiovascular vulnerability. [5]
Causal or Coincidence?
Recent work using genetic models has added depth to our understanding. One recent Mendelian randomization analysis utilized genetic markers to evaluate whether there's a true causal relationship between hormone imbalance and cardiovascular changes. The data suggest that even genetically predicted low hormone levels are associated with increased cardiovascular risk, strengthening the argument that this is more than a coincidental association. [6]
What About Borderline Cases?
Some individuals present with only a mild increase in TSH, while primary hormone levels (T4 and T3) remain within the normal range. For a long time, test results like this (subclinical hypothyroidism) were considered benign. However, newer evidence indicates that individuals with early-stage hormone imbalance often show increased thickness in blood vessel walls, less favorable lipid ratios, impaired blood sugar regulation, and markers of oxidative stress. [7] All of these factors are contributors to cardiovascular risk.
In short, even early hormonal changes may exert subtle but measurable effects on heart structure and function, particularly when other risk factors are present.
Clinical Implications
Interventions for overt hormone deficiency are widely accepted as beneficial for both symptom relief and longevity. However, the decision to address early-stage or borderline cases remains more complex. A patient with subclinical hypothyroidism may be a good candidate for intervention if:
- Regulatory hormone levels (TSH) continue to exceed the normal range over time, even if T4 levels stay normal.
- Other cardiovascular risk factors are evident (ex. dysregulated blood pressure, elevated cholesterol, or family history of cardiovascular issues).
- Symptoms that mimic hypothyroidism occur, such as fatigue, slow heart rate, cold intolerance, or mood changes.
- Autoimmune markers affecting the gland are detectable. [8]
The Takeaway: Thyroid Hormones and Heart Health
The relationship between this key regulator of metabolism and cardiovascular health is increasingly supported by clinical evidence. When thyroid hormone levels drop, even modestly, the heart may be forced to adapt in ways that compromise efficiency, increase metabolic strain, and elevate long-term risks.
For healthcare practitioners, this means paying close attention to regulatory hormone trends (i.e. TSH) and not overlooking early signs or borderline cases of hypothyroidism. In addition, many cases of subclinical hypothyroidism are asymptomatic, so those with evolving cardiovascular profiles should also be monitored also for thyroid health. [8]
For individuals looking to optimize long-term health, routine screening and early detection of hormone imbalances may offer an important window of intervention and a stronger cardiovascular future.
Disclaimer:
The information provided is for educational purposes only. Consult your physician or healthcare practitioner if you have specific questions before instituting any changes in your daily lifestyle including changes in diet, exercise, and supplement use.
Allison Sayre is a board-certified women’s health nurse practitioner with advanced expertise in hormonal health, integrative gynecology, and patient-centered care across the lifespan. She holds a Master of Science in Nursing and has served as both a clinical provider and educator in functional and conventional women’s health settings.
Allison has led clinical programming, practitioner training, and content development for leading health brands and organizations. Her work bridges the clinical and commercial worlds, helping translate scientific evidence into practical tools for healthcare practitioners. At ARG, Allison contributes to medical education, clinical protocol development, and strategic content that supports the evolving needs of women's healthcare practitioners.