The Coimbra Protocol: Overcoming Vitamin D Resistance in Autoimmune Disease

The Coimbra Protocol, developed by Brazilian neurologist Dr. Cícero Galli Coimbra, represents a therapeutic approach to autoimmune disease based on the administration of pharmacological doses of vitamin D3. Unlike conventional vitamin D supplementation aimed at correcting deficiency, the protocol is designed to overcome an acquired resistance to vitamin D at the cellular level, a condition Dr. Coimbra hypothesizes underlies the development of autoimmunity. By administering individualized high doses of vitamin D3 ranging from 40,000 to 300,000 IU daily under strict medical supervision with concomitant low-calcium diet and aggressive hydration, the protocol aims to restore immune tolerance and arrest disease progression. This essay explores the protocol's foundational hypothesis, the immunological mechanisms by which vitamin D modulates immune function, the published safety data from a cohort of over 300 patients, the practical requirements for implementation, and the controversies surrounding this unproven but increasingly utilized intervention.

---

1. Introduction: The Neurologist Who Challenged Autoimmunity

Dr. Cícero Galli Coimbra is a neurologist and professor at the Federal University of São Paulo, Brazil, who has spent over two decades developing a clinical protocol for treating autoimmune diseases through the restoration of adequate systemic vitamin D levels. His journey began not with autoimmunity but with brain ischemia research during his postdoctoral program at Lund University in Sweden in 1991. While immersed in the neuroscience literature, Coimbra became struck by a recurring observation: therapeutic advances demonstrated in clinical and experimental research were rarely translated into clinical practice, despite their immediate applicability.

Through his reading of the medical literature, Coimbra became convinced that vitamin D could be a fundamental therapeutic resource, particularly because it stimulates the production of regenerative substances in the brain. In 2001, he began administering vitamin D at physiological doses of 10,000 IU daily to patients with Parkinson's disease, a dose approximating what the body produces during brief sun exposure. A serendipitous observation changed the trajectory of his work. One patient returned for follow-up after three months on 10,000 IU daily. This patient also suffered from vitiligo, an autoimmune skin condition, and Coimbra noticed that a large facial lesion present at the previous visit had become barely visible. The lesion had nearly disappeared within months of vitamin D administration.

Coimbra investigated the literature on vitamin D's effects on the immune system and found a significant body of published research indicating an important immunoregulatory role for this powerful substance. Since multiple sclerosis is the most common neurological autoimmune disease, he began prescribing vitamin D to MS patients with doses around 10,000 IU daily and observed remarkable clinical improvement in the vast majority. From there, doses were gradually increased, always supported by laboratory monitoring to ensure patients experienced no side effects. The results were that many patients became completely free of disease symptoms and manifestations. Over the next decade, Coimbra and his team gradually modified and refined the treatment, particularly in terms of daily prescribed doses, which increased progressively. By 2012, the desired level of efficacy was achieved, and the Coimbra Protocol became substantially what it is today.

2. The Foundational Hypothesis: Acquired Vitamin D Resistance

The central theoretical framework underlying the Coimbra Protocol is the hypothesis of an acquired, non-hereditary form of vitamin D resistance as a fundamental cause of autoimmune disease. This hypothesis, elaborated in detail by Lemke and colleagues in a 2021 paper published in Frontiers in Immunology, proposes that individuals developing autoimmune conditions have a diminished biological response to vitamin D that cannot be overcome by conventional supplementation doses.

The concept of vitamin D resistance is not new. In 1937, Albright, Butler, and Bloomberg first proposed the idea based on observations that rare cases of rickets in children required very high vitamin D doses to relieve symptoms. Subsequently, it was shown that resistance to 1,25-dihydroxyvitamin D in such children is frequently caused by hereditary vitamin D receptor defects resulting in hypocalcemia, secondary hyperparathyroidism, rickets, and alopecia. However, these hereditary forms are extremely rare and diagnosed in childhood.

The acquired vitamin D resistance hypothesized by Coimbra differs fundamentally. It is proposed to develop during aging based on an interaction between genetic susceptibility polymorphisms within the vitamin D system and an accumulation of environmental factors that further impair the hormonal signaling of vitamin D-derived metabolites. This form of resistance would be far more common, consistent with the frequency of susceptibility polymorphisms and the rising incidence of autoimmune diseases.

Evidence for variable vitamin D responsiveness comes from the work of Carlberg and colleagues in two intervention studies. In the VitDmet study, 71 elderly prediabetic individuals were supplemented with 0, 1600, or 3200 IU vitamin D3 daily over five months. Using biomarkers including mRNA expression of vitamin D-regulated genes and laboratory parameters, the researchers demonstrated that even supposedly adequate high doses of 3200 IU were unable to exert expected vitamin D-regulatory effects in all subjects. Focusing on the PTH feedback system alone, 25 percent of patients showed no adequate response. When considering all 36 tested parameters, patients clustered into 24 percent low responders, 51 percent mid responders, and 25 percent high responders. The VitDbol study replicated these findings in healthy Finnish students receiving an 80,000 IU bolus dose, with similar low responder rates.

These data provide in vivo confirmation of a spectrum of vitamin D responsiveness, with approximately one quarter of any given population not responding adequately to conventional vitamin D doses. Vitamin D resistance, as proposed by Coimbra, represents the extreme low-response end of this spectrum. Individuals with vitamin D resistance would require very high supplementation doses to achieve adequate physiological response, such as reduction of PTH concentrations or down-regulation of an activated adaptive immune system.

3. The Vitamin D System and Immune Modulation

Understanding the Coimbra Protocol requires appreciation of the complex role vitamin D plays in immune function. Vitamin D3 is a secosteroid and prohormone obtained from food or, primarily, through endogenous production in skin exposed to ultraviolet B radiation. Upon reaching the blood, vitamin D3 binds to vitamin D binding protein and is transported to the liver, where it is hydroxylated to its storage form, 25-hydroxyvitamin D3 or calcidiol, the main laboratory parameter for assessing vitamin D status. Concentrations below 20 nanograms per milliliter are considered deficient, while 40 to 60 nanograms per milliliter are considered ideal.

In various tissues, particularly the kidneys, 25-hydroxyvitamin D3 is further hydroxylated to the biologically active hormone calcitriol or 1,25-dihydroxyvitamin D3. Beyond its well-described role in calcium and phosphate homeostasis, calcitriol exerts multiple pleiotropic effects, particularly within the immune system. Mediated by the vitamin D receptor expressed on immune cells, calcitriol influences immune function, cellular differentiation, and growth.

The immunomodulatory effects of vitamin D are profound and multifaceted. Binding of calcitriol to the vitamin D receptor inhibits differentiation and proliferation of B lymphocytes and T helper lymphocytes, promoting a shift from an inflammatory to a more tolerant immune status. Specifically, vitamin D increases regulatory T cells, which suppress inflammation, and decreases Th17 cells, which drive autoimmunity. This rebalancing of the T-cell ratio toward immune tolerance is central to the therapeutic rationale of the Coimbra Protocol.

More recent research has revealed alternative pathways of vitamin D metabolism mediated by the mitochondrial enzyme CYP11A1, which hydroxylates the side chain of vitamin D. The main product, 20-hydroxyvitamin D3, serves as substrate for further hydroxy-derivatives. These nonclassical metabolites also act as hormones, functioning as partial agonists of the vitamin D receptor while having high affinity as agonists of the aryl hydrocarbon receptor and as inverse agonists of the retinoid-related orphan receptors RORα and RORγ. These receptors are expressed by inflammatory Th17 cells, where they synergistically regulate differentiation and inflammatory cytokine production, notably interleukin-17, implicated in autoimmune disorders including psoriasis and multiple sclerosis. The binding of vitamin D metabolites to both RORα and RORγ results in interleukin-17 inhibition, providing another mechanism distinct from vitamin D receptor signaling by which vitamin D may protect against or alleviate autoimmune disease symptoms.

4. Diagnosis of Vitamin D Resistance: The Role of Parathyroid Hormone

A hallmark of acquired vitamin D resistance, if it exists, would be an elevated parathyroid hormone concentration despite 25-hydroxyvitamin D levels being in the ideal range, indicating sufficient production of calcitriol. Understanding this requires appreciation of the calcium-vitamin D-PTH feedback loop.

One key role of calcitriol is to enhance intestinal calcium absorption. When ionized calcium concentrations in blood are low, the parathyroid glands release parathyroid hormone, which stimulates calcium release from bones. Furthermore, parathyroid hormone increases conversion of 25-hydroxyvitamin D to calcitriol in the kidneys and inhibits tubular reabsorption of phosphate, lowering water-insoluble calcium-phosphate salts and increasing ionized calcium concentrations. Parathyroid hormone thus constitutes a direct feedback mechanism within the vitamin D system.

A physiological 25-hydroxyvitamin D level should suppress parathyroid hormone into the lower third of the reference range. In other words, if 25-hydroxyvitamin D levels are high, parathyroid hormone should be low, and vice versa. In patients with autoimmune diseases, this negative feedback loop is disturbed. Based on these observations, Coimbra proposed that parathyroid hormone concentrations serve as the key biomarker for individual vitamin D dosing and its effect on calcium metabolism.

According to the hypothesis, for optimal physiological response of calcitriol, a low parathyroid hormone plateau should be reached and maintained within the lower third of the reference range. The degree of parathyroid hormone suppression guides dose titration, with the goal of achieving the minimum parathyroid hormone level that indicates adequate vitamin D activity at the cellular level without inducing hypercalcemia.

5. The Protocol in Practice: Dosing and Monitoring

The Coimbra Protocol involves administration of pharmacological doses of vitamin D3 on an individualized basis, accompanied by strict dietary and hydration requirements and regular laboratory monitoring. According to Coimbra and co-workers after two decades of clinical experience, doses range from 40,000 to 300,000 IU per day, with the conventional starting dose in multiple sclerosis approximately 1,000 IU per kilogram body weight daily. For other autoimmune diseases including rheumatoid arthritis, psoriatic arthritis, connective tissue diseases, plaque psoriasis, and inflammatory bowel diseases, starting doses range from 300 to 1,000 IU per kilogram daily. Autoimmune thyroid inflammation receives lower starting doses of 150 to 300 IU per kilogram daily, which also serves as the typical pediatric starting dose across diagnoses.

Before initiating the protocol, patients undergo comprehensive baseline laboratory evaluation including complete blood count, ferritin, albumin, renal and liver function tests, cystatin C, 25-hydroxyvitamin D, parathyroid hormone, electrolytes including serum calcium and phosphate, vitamin B12, selenium, thyroid hormones, TSH, and 24-hour urinary calcium excretion. Baseline bone densitometry is also performed. Contraindications include impaired renal function, disturbed calcium metabolism, unwillingness or inability to maintain adequate daily fluid intake, and refusal to restrict dietary calcium.

The critical safety framework comprises three essential components. First, patients must adhere to a strict low-calcium diet, eliminating all dairy products and other high-calcium foods including calcium-fortified plant milks. Total daily calcium intake is restricted to approximately 500 to 600 milligrams. Second, patients must consume a minimum of 2.5 liters of low-calcium fluid daily, with calcium content below 200 milligrams per liter. This volume must be increased during fever, profuse sweating from any cause, or gastrointestinal infection, and must be maintained even during long-haul flights or extended travel. Third, regular monitoring of serum and urinary calcium, renal function, and parathyroid hormone is mandatory, with frequency determined by the supervising physician.

6. Published Safety Data: The 2022 Cohort Study

Concerns about hypercalcemia and subsequent impaired renal function have been the major objections raised against the Coimbra Protocol. In 2022, Amon and colleagues published the first comprehensive safety analysis in Nutrients, reporting retrospective data from 319 patients with a broad spectrum of autoimmune diseases treated according to the protocol for up to 3.5 years at a certified center in Germany.

The study population had a mean age of 43.3 years, with 65.5 percent female and 34.5 percent male patients. Principal diagnoses included vitiligo, multiple sclerosis, psoriasis, and other autoimmune conditions. The mean daily vitamin D3 dose was 35,291 IU, with substantial individual variation reflected in a standard deviation of 21,791 IU. Analysis of more than 6,100 individual laboratory parameters demonstrated that all mean values remained within normal ranges throughout the treatment period.

Serum total calcium averaged 2.4 millimoles per liter, serum creatinine 0.8 milligrams per deciliter, estimated glomerular filtration rate 92.5 milliliters per minute, serum cystatin C 0.88 milligrams per liter, and 24-hour urinary calcium excretion 6.9 millimoles per 24 hours. Importantly, the researchers found a very weak relationship between oral vitamin D3 dosage and subsequent calcium levels, both in serum and in 24-hour urinary excretion. This finding supports the hypothesis that vitamin D-resistant patients have intrinsic protection against hypercalcemia, as the resistance applies not only to immune effects but also to calcemic effects.

As expected from the protocol's rationale, parathyroid hormone levels decreased over time during treatment, depending on vitamin D3 dose. In multiple sclerosis patients, parathyroid hormone plateaued at approximately 15 picograms per milliliter around six months after treatment initiation, which differed from the pattern observed in non-MS autoimmune patients. This suppression into the lower reference range confirms the biological activity of the administered vitamin D at the cellular level.

Genetic analysis of a patient subgroup revealed that the most frequent mutations occurred in genes encoding the enzymes 25-hydroxylase and 1-alpha-hydroxylase, affecting 75 percent of all patients. Single nucleotide polymorphisms in the vitamin D receptor regions were detected less frequently. This distribution supports the hypothesis that multiple genetic variations within the vitamin D system contribute to individual vitamin D resistance, requiring higher circulating 25-hydroxyvitamin D levels to achieve biologically active calcitriol concentrations sufficient for normalized immune function.

7. Evidence for Clinical Efficacy

While the 2022 safety study focused on laboratory parameters rather than clinical outcomes, the foundational 2013 pilot study from Coimbra's group documented clinical improvements in autoimmune skin disorders. Twenty-five patients received 35,000 IU vitamin D3 daily for six months with low-calcium diet and adequate hydration. In nine psoriasis patients, 25-hydroxyvitamin D levels increased from 14.9 to 106.3 nanograms per milliliter, parathyroid hormone decreased from 57.8 to 28.9 picograms per milliliter, and clinical status measured by the Psoriasis Area and Severity Index improved significantly. In sixteen vitiligo patients, 25-hydroxyvitamin D increased from 18.4 to 132.5 nanograms per milliliter, parathyroid hormone decreased from 55.3 to 25.4 picograms per milliliter, and repigmentation improved significantly.

The Lemke hypothesis paper published in 2021 reviewed observational and mechanistic evidence for acquired vitamin D resistance, focusing on clinical confirmation from treating multiple sclerosis patients with the Coimbra Protocol. The authors argued that acquired vitamin D resistance provides a plausible pathomechanism for autoimmune disease development and that high-dose vitamin D therapy offers the only effective approach to overcome this resistance. They noted that approximately 60 percent of multiple sclerosis patients in their experience had an average of six vitamin D-related gene polymorphisms requiring higher doses for therapeutic effect.

8. Adverse Events and Case Reports

Despite the reassuring safety data from the large cohort study, individual case reports document potential serious adverse effects from unsupervised or inappropriately managed high-dose vitamin D intake. Feige and colleagues published a 2019 case report in Multiple Sclerosis Journal describing a patient with primary progressive multiple sclerosis who developed generalized weakness caused by hypercalcemia after uncontrolled intake of more than 50,000 IU cholecalciferol daily for several months. Multiple treatment strategies were required to normalize serum calcium, yet renal function only partially improved, and multiple sclerosis worsened during the episode. This case underscores the critical importance of medical supervision, appropriate patient selection, and adherence to the full protocol including dietary restrictions and hydration.

A 2023 case report in Neurotoxicology and Teratology documented vitamin D hypervitaminosis in pregnancy following use of the Coimbra Protocol for ulcerative colitis. A 31-year-old pregnant woman treated with 100,000 IU cholecalciferol daily, along with magnesium, vitamin B2, vitamin K, omega-3 fatty acids, low-calcium diet, and 2.5 liters of low-calcium water daily, was referred to a teratology information service at eight weeks gestation. She reported good clinical control of her ulcerative colitis. This represented the first well-documented case of an infant born to a mother on the Coimbra Protocol and the first documented case of maternal milk vitamin D hypervitaminosis. The infant experienced mild toxic effects but ultimately remained healthy after hospitalization. The authors emphasized the lack of evidence for vitamin D macro dosing in ulcerative colitis and the importance of informing patients about this uncertainty.

9. Controversies and Criticism

The Coimbra Protocol remains highly controversial within conventional medicine. A small group of physicians, estimated at less than 0.1 percent, promotes the protocol, while the majority considers it an ineffective and potentially dangerous procedure. Major concerns include the risk of life-threatening complications such as renal failure, cardiac arrhythmia, and epileptic status from vitamin D toxicity manifesting as fatigue, muscle weakness, or urinary dysfunction.

In June 2021, Coimbra faced provisional revocation of his medical registration by the Regional Medical Council of the State of São Paulo following ethical and professional proceedings conducted under secrecy. The sanction notification cited unspecified ethical violations, prompting activists to call for strict action against pseudosciences that indebt families and endanger children and adolescents. The disciplinary action remains a point of contention, with supporters viewing it as persecution of an innovator and critics citing it as evidence of the protocol's problematic nature.

Scientific criticism emphasizes the lack of randomized controlled trials demonstrating efficacy. While the 2013 pilot study showed clinical improvement, it lacked a control group, and no subsequent controlled trials have been published. The 2022 safety study, while providing important reassurance regarding laboratory parameters under expert supervision, did not assess clinical outcomes. The hypothesis of acquired vitamin D resistance, while supported by the Carlberg responder studies and genetic polymorphism data, has not been definitively proven as the underlying mechanism of autoimmune disease.

A 2020 critical analysis by Feige and colleagues in Nutrients examined vitamin D supplementation in multiple sclerosis, concluding that while epidemiological studies consistently associate low vitamin D levels with increased MS risk and disease activity, interventional trials have yielded inconsistent results. They noted that a single randomized trial published in 2025 showed benefit in multiple sclerosis specifically, potentially validating vitamin D's role in this disease while leaving other autoimmune applications less supported.

Critics also point to the correlation-causation problem eloquently summarized by F. Perry Wilson on Medscape. Study after study across diseases from Alzheimer's to Zika virus infection has demonstrated that low vitamin D is a risk factor for unfavorable outcomes, yet randomized trials correcting low levels generally fail to improve patient outcomes. The explanation is that low vitamin D correlates with poor health rather than causing it, representing the classic case of correlation versus causation. However, Wilson acknowledged that new data from a randomized trial in multiple sclerosis may require reevaluation of these assumptions, at least for this specific disease.

10. Conclusion

The Coimbra Protocol represents a bold and scientifically grounded attempt to address autoimmune disease through the lens of vitamin D resistance and high-dose replacement therapy. Dr. Cícero Coimbra's clinical observations over two decades, supported by the Carlberg responder studies demonstrating variable individual vitamin D responsiveness, and the Lemke hypothesis linking genetic polymorphisms to acquired resistance, provide a coherent theoretical framework for understanding why some patients require pharmacological vitamin D doses to achieve immune modulation.

The 2022 safety study published in Nutrients with over 300 patients followed for up to 3.5 years provides substantial reassurance that, under appropriate medical supervision with strict adherence to low-calcium diet and aggressive hydration, the protocol can be implemented without causing hypercalcemia or renal impairment in the majority of patients. The weak relationship between vitamin D dose and calcium levels supports the resistance hypothesis and suggests that vitamin D-resistant patients have intrinsic protection against the calcemic effects that would otherwise limit dosing.

Yet important questions remain unanswered. The absence of randomized controlled trials demonstrating clinical efficacy means that the protocol remains unproven by conventional evidence standards. The case reports of toxicity in unsupervised settings and during pregnancy highlight the real dangers when the full protocol is not followed or when patients are inappropriate candidates. The disciplinary action against Coimbra raises questions about professional conduct that remain unresolved due to confidentiality.

Patients with autoimmune diseases, particularly multiple sclerosis, often seek holistic and alternative approaches beyond symptomatic, immunosuppressive, and disease-modifying treatments. The extensive information available on the internet and numerous personal case reports reflect patient-perceived efficacy as seen in social media. However, the increasing interest in ultra-high-dose vitamin D also raises concerns about possible consequences of self-administering highly concentrated supplements without medical supervision.

The Coimbra Protocol should not be viewed as a first-line treatment or a replacement for evidence-based therapy, but rather as an option for carefully selected patients under close specialist supervision after conventional interventions have proven ineffective, consistent with the Declaration of Helsinki provisions for unproven interventions. The message must be especially clear regarding interventions with documented health risks: medical supervision, appropriate patient selection, adherence to dietary restrictions, and regular laboratory monitoring are non-negotiable requirements. For those who meet these criteria, the protocol offers a potential pathway to immune rebalancing that, based on available evidence, appears reasonably safe when properly implemented and may offer hope where conventional approaches have failed.

11. Key Published Works and Resources

Publication: Finamor DC, et al. A pilot study assessing the effect of prolonged administration of high daily doses of vitamin D on the clinical course of vitiligo and psoriasis. Dermatoendocrinol. 2013.

Publication: Lemke D, et al. Vitamin D Resistance as a Possible Cause of Autoimmune Diseases: A Hypothesis Confirmed by a Therapeutic High-Dose Vitamin D Protocol. Frontiers in Immunology. 2021.

Publication: Amon U, et al. Safety Data in Patients with Autoimmune Diseases during Treatment with High Doses of Vitamin D3 According to the "Coimbra Protocol". Nutrients. 2022.

Case Report: Feige J, et al. Life-threatening vitamin D intoxication due to intake of ultra-high doses in multiple sclerosis: A note of caution. Multiple Sclerosis Journal. 2019.

Case Report: Vitamin D macro dosing in pregnancy: A case report of D hypervitaminosis in pregnancy according to non-conventional Coimbra protocol and perinatal toxicity. Neurotoxicology and Teratology. 2023.

Website: Official Coimbra Protocol website at coimbraprotocol.com

Clinical Resource: GrassrootsHealth educational materials on vitamin D and immune function