Why Hashimoto’s Fatigue Persists Even With “Normal” Labs — and the Thiamine Link No One Fully Explains
- thyvita health
- Feb 11
- 4 min read
Cellular uptake is the cell’s ability to absorb and use nutrients. In Hashimoto’s, low stomach acid and inflammation interfere with this process, leaving cells undernourished even when intake appears adequate. This article explains how impaired uptake—especially of thiamine—contributes to chronic fatigue in thyroid patients.
Chronic fatigue is one of the most disabling symptoms reported by people with Hashimoto’s thyroiditis and those who have undergone thyroidectomy. And yet, it is often the least explained.
Patients are told their thyroid labs are “normal.”Medication is adjusted.Nothing changes.
But clinical research — and patient physiology — point to a different mechanism entirely.
Italian physician Antonio Costantini identified a consistent pattern across inflammatory and autoimmune diseases: the chronic fatigue that accompanies these conditions is associated with a mild thiamine (vitamin B1) deficiency.
What his work did not fully explore is why that deficiency develops so reliably in Hashimoto’s patients — and why it often goes undetected.
The missing piece is digestion.
Who Is Dr. Antonio Costantini?
Antonio Costantini was an Italian medical doctor known for his clinical research on thiamine (vitamin B1) and chronic fatigue in inflammatory and autoimmune diseases. Rather than working in academia for grants or prestige, Costantini was a front-line clinician who focused on patient outcomes. Over many years, he observed that patients with conditions such as Hashimoto’s thyroiditis, multiple sclerosis, Parkinson’s disease, and inflammatory bowel disease shared a common symptom: profound, persistent fatigue that did not respond to conventional treatment. His peer-reviewed case studies and clinical reports consistently showed that restoring thiamine—often at therapeutic doses—led to rapid and meaningful improvements in fatigue, even when patients did not appear deficient on standard lab tests. His work helped introduce the concept of functional (cellular) thiamine deficiency into autoimmune and neurological care.
Hashimoto’s Quietly Disrupts Digestion First
Hashimoto’s is not only a thyroid disorder. It is a chronic inflammatory autoimmune disease, and inflammation has consequences far beyond hormone output.
One of the earliest and most overlooked effects is reduced stomach acid production.
Low stomach acid (hypochlorhydria) is extremely common in:
Hashimoto’s thyroiditis
Post-thyroidectomy patients
Long-standing hypothyroid states
This matters because stomach acid is not optional. It is required to:
Release vitamins from food
Absorb B-vitamins effectively
Ionize minerals needed for enzyme activation
Protect the gut from bacterial overgrowth
When stomach acid drops, nutrient absorption fails long before lab values reflect a problem.
Low Stomach Acid → Nutrient Deficiency → Thiamine Failure
Thiamine is especially vulnerable in low-acid states.
Here’s the direct chain:
Low stomach acid prevents proper thiamine release and absorption
Minerals required to activate thiamine (especially magnesium) are depleted
Thiamine enters the bloodstream poorly or remains inactive
Cells cannot utilize thiamine effectively
Mitochondrial energy production slows
Fatigue becomes chronic and disproportionate
This is what researchers call a functional or cellular thiamine deficiency.
Blood levels may appear “normal.”Dietary intake may be adequate.But the cell cannot use the nutrient.
That distinction explains why fatigue persists despite “normal labs.”
What Dr. Costantini Actually Found
In multiple peer-reviewed clinical observations involving autoimmune and inflammatory diseases — including Hashimoto’s thyroiditis — Dr. Costantini found that restoring thiamine dramatically improved chronic fatigue, sometimes within days.
Importantly:
Patients were not classically malnourished
Standard laboratory testing did not show deficiency
The issue was utilization, not intake
His work demonstrated that autoimmune inflammation creates a mild but functionally significant thiamine deficiency at the cellular level.
What Hashimoto’s physiology adds to this picture is the mechanism:low stomach acid creates the nutrient deficiency that prevents thiamine from being used in the first place.
Why Thiamine Is So Critical for Thyroid Patients
Thiamine is essential for:
Mitochondrial ATP production
Carbohydrate metabolism
Nervous system signaling
Autonomic balance and stress response
When thiamine utilization is impaired:
ATP production drops
Fatigue becomes constant
Brain fog, weakness, and exercise intolerance appear
Patients feel “unwell” despite normal thyroid markers
This is why thyroid hormone replacement alone often fails to restore energy.
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Why Megadosing Thiamine Isn’t the Full Solution
Dr. Costantini’s work showed that high-dose thiamine could temporarily overcome this utilization block. But that approach bypasses — rather than repairs — the underlying problem.
If low stomach acid and broader nutrient depletion persist:
Thiamine benefits may plateau or fade
Other energy-limiting deficiencies remain
Fatigue returns
Sustainable recovery requires rebuilding the nutrient environment, not forcing one nutrient in isolation.
Why Women’s Ultra Fits This Physiology
This is where Women’s Ultra is uniquely appropriate for Hashimoto’s and thyroidectomy patients.
Women’s Ultra:
Contains thiamine (vitamin B1) to directly support energy metabolism
Provides B-complex nutrients that work synergistically — not in isolation
Includes key mineral cofactors required for thiamine activation and enzyme function
Is formulated specifically for people with impaired digestion and absorption, not ideal digestive conditions
Rather than treating fatigue as a single-nutrient problem, Women’s Ultra supports:
Correction of nutrient deficiencies caused by low stomach acid
Improved cellular utilization of thiamine
Restoration of mitochondrial energy pathways
Broad metabolic support in autoimmune and post-thyroidectomy states
This is why Women’s Ultra is not “just a multivitamin” — and why it is particularly relevant for patients with Hashimoto’s or no thyroid at all.
The Takeaway
Chronic fatigue in Hashimoto’s is not vague, psychological, or unexplained.
It follows a clear physiological sequence:
Hashimoto’s → low stomach acid → nutrient deficiency → impaired thiamine utilization → cellular energy failure → chronic fatigue
Dr. Costantini identified the thiamine connection.Digestive physiology explains why it happens.Targeted nutrient repletion explains how to move forward.
When fatigue is viewed through this lens, the experience of thyroid patients finally makes sense — and so does the solution.
It's important to note: Fatigue in Hashimoto’s isn’t about one missing nutrient. Thiamine is just the signal. Low stomach acid and chronic inflammation create widespread nutrient deficiencies that prevent cells from making energy at all. This article explains why thiamine shows up in the research—and why restoring overall nutrient uptake is the real solution for thyroid patients who still feel exhausted.
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References / Citations
Costantini A, Pala MI. Thiamine and fatigue in autoimmune disease.Journal of Alternative and Complementary Medicine, 2013.
Costantini A et al. High-dose thiamine improves fatigue in chronic inflammatory diseases.BMJ Case Reports, 2013.
Lonsdale D, Marrs C. Thiamine Deficiency Disease, Dysautonomia, and High Calorie Malnutrition.
Heidelbaugh JJ. Hypochlorhydria and nutrient malabsorption.Cleveland Clinic Journal of Medicine.
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