Vitamin D

After looking at the importance of supplements for people living with Hidradenitis Suppurativa in the previous article, let us explore why vitamin D deserves particular attention.

Vitamin D: What Is It?

Despite its name, vitamin D acts more like a prohormone, or a precursor to a hormone.
Vitamin D and vitamin D deficiency have attracted growing interest in recent years. In addition to its established role in maintaining bone health, vitamin D is involved in the normal function of the immune system. Epidemiological studies have found associations between low vitamin D levels and several immune-mediated conditions, but an association does not prove that low vitamin D causes a condition or that supplementation can treat it.

Vitamin D and Immune-Mediated Conditions

How Vitamin D Affects the Immune System

Genetic, immunological, hormonal, and environmental factors are thought to contribute to the development of autoimmune diseases.

One environmental factor researchers have studied is vitamin D. Vitamin D has a significant role in several immune system processes, and vitamin D receptors are found on immune cells, including macrophages, dendritic cells, B cells, and T cells.

Laboratory studies have examined how vitamin D affects immune cells such as neutrophils, dendritic cells, and regulatory T cells, or Tregs. In these in vitro models, vitamin D has shown an inhibitory effect on Th1 cells, with a reduction in the production of certain Th1 cytokines. These laboratory findings do not by themselves establish a clinical treatment effect.

Vitamin D also appears to influence signaling between lymphocytes and other cells, including pathways involving Th2 cells and dendritic cells associated with immune tolerance, which may contribute to anti-inflammatory and immune-regulating activity.

Evidence also suggests that vitamin D can modulate the activity of Th17 cells, which are involved in autoimmune inflammation, and may support Treg activity, thereby contributing to immune tolerance.

In one in vitro study, vitamin D was found to reduce the production and secretion of autoantibodies. This was a laboratory finding and should not be read as evidence that vitamin D supplements treat autoimmune disease in people.

Vitamin D and Hidradenitis Suppurativa

In one study of people with Hidradenitis Suppurativa, researchers measured serum 25-hydroxyvitamin D and found that 75% of participants had levels below 50 nmol/L (20 ng/mL). This suggests that low vitamin D may be common in some HS populations, but it does not show that deficiency causes HS or that supplementation improves HS. HS is a chronic autoinflammatory condition, not simply an autoimmune disease, and it has no definitive cure.

Vitamin D Deficiency

Causes

Low vitamin D levels can have several causes. They may be related to:

• Low dietary intake of vitamin D;
• Limited sun exposure, which may be associated with:
  • Spending little time physically active outdoors;
  • Darker skin;
  • Living far from the equator;
  • Consistent use of sun protection, which reduces vitamin D production in the skin. Sun protection remains important for preventing skin damage, so do not stop using it to raise vitamin D levels.
• Higher vitamin D requirements during certain life stages or health circumstances;
• Reduced intestinal absorption
• Medical conditions such as liver disease or kidney disease, which can interfere with the body's processing and activation of vitamin D;
• Treatment with medications that affect vitamin D absorption or metabolism, such as certain anticonvulsants, cholestyramine, glucocorticoids, antifungals, antivirals, and anti-rejection medicines.

Risk Factors

Several factors can increase the risk of low vitamin D levels, including:

• Smoking
• Older age
• Obesity, because a higher amount of body fat is associated with lower circulating vitamin D levels;
• Darker skin, because melanin reduces the skin's production of vitamin D from sunlight;
• Alcohol dependence, which may be associated with poor nutrition, liver disease, or impaired absorption;
• Osteoporosis;
• Exclusive or prolonged breastfeeding without the vitamin D supplementation recommended by a pediatric healthcare professional, because breast milk alone usually provides little vitamin D;
• Crohn's disease or celiac disease, because these conditions can reduce intestinal absorption of vitamin D;
• Gastric bypass surgery, because it can reduce vitamin D absorption in the digestive tract.
• Increased intestinal permeability may be discussed in some health contexts, but it should not be assumed to be the cause of a vitamin D deficiency without medical assessment.

Diagnosis

To assess vitamin D status, clinicians measure the serum concentration of 25-hydroxyvitamin D, also called calcidiol or 25-OH-D.

25-hydroxyvitamin D is the main form used to assess vitamin D from sunlight, food, and supplements in the bloodstream.
Its concentration is commonly reported in either nanomoles per liter, written as nmol/L, or nanograms per milliliter, written as ng/mL.

Interpretation can vary by guideline, laboratory, age, health status, and clinical context. One widely used reference considers levels below 30 nmol/L (12 ng/mL) consistent with deficiency risk, levels from 30 to below 50 nmol/L (12 to below 20 ng/mL) potentially inadequate, and levels of at least 50 nmol/L (20 ng/mL) adequate for most people. Higher is not always better, and a healthcare professional should interpret your result.

The Coimbra Protocol

IMPORTANT: this section is for information only. When I discuss ordinary vitamin D supplementation, I am not referring to this protocol. The Coimbra protocol uses very high doses and can cause serious harm without specialist medical supervision. I am not a doctor, and this article is not medical advice.

The Coimbra protocol uses high doses of vitamin D in an attempt to manage several immune-mediated conditions. Claims that it can rebalance the immune system or treat these conditions have not been established by robust clinical evidence. It should not be considered a cure for HS or any other disease.

How the Protocol Began

The high-dose vitamin D approach was developed by neurologist Cicero Galli Coimbra. While exploring possible approaches to neurodegenerative conditions, Coimbra reviewed research on vitamin D that was not part of routine clinical practice. He believed some patients might benefit from applying these ideas and began prescribing what were considered high doses, around 10,000 IU, to people with neurodegenerative conditions such as Parkinson's disease. This is a historical account of the protocol's development, not evidence that the approach is effective or safe.

His reasoning was that the body can produce 10,000 IU or more of vitamin D after a period of sun exposure, so he believed a similar oral dose would not necessarily be toxic. However, vitamin D produced through sunlight is regulated differently from vitamin D taken as a supplement. Current guidance for the general adult population sets a tolerable upper intake level of 4,000 IU per day unless a clinician prescribes and monitors a different dose. Natural production after sun exposure does not make an equivalent supplement dose automatically safe.

The First Reported Success and Later Developments

Coimbra reported that one person with Parkinson's disease who had been prescribed 10,000 IU returned for follow-up after several months with an improvement in clinical symptoms and regression of some vitiligo patches.

This anecdotal observation prompted him to look more closely at vitamin D, the immune system, and autoimmune disease. Vitamin D does help regulate immune function and gene expression in immune cells, but a single reported experience cannot establish that a treatment works.

Coimbra then used 10,000 IU of vitamin D3 in people with autoimmune conditions and reported varying degrees of benefit, although he believed this dose did not alter disease progression. He later increased doses gradually and tailored them according to each person's response, using parathyroid hormone, or PTH, as one monitoring marker. Some doses reportedly exceeded 50,000 IU. These amounts are far above the general adult upper intake level and can cause hypercalcemia, kidney damage, soft tissue calcification, heart rhythm problems, and other serious complications.

The neurologist used an initial dose and adjusted it after a few months, increasing or decreasing it according to PTH levels, which the protocol sought to keep near the lower end of the reference range. PTH alone does not make high-dose vitamin D safe. Anyone considering or already following such a regimen needs close supervision from a qualified physician, with appropriate calcium, kidney, and other laboratory monitoring.

Conclusion

Vitamin D has an important role in normal immune function. Molecular studies show that vitamin D can act as an immunomodulator, but laboratory mechanisms do not automatically translate into clinical benefits from supplementation.

Maintaining an appropriate vitamin D level supports general health, especially bone health. Low vitamin D levels have been observed in people with multiple sclerosis, type 1 diabetes, inflammatory bowel disease, psoriasis, Hidradenitis Suppurativa, and other conditions. These associations do not prove that low vitamin D causes disease activity or that supplements improve outcomes.

Vitamin D supplements can be useful when a deficiency or increased need has been identified, but they are not risk-free. Excessive intake can cause serious toxicity. For most adults, 4,000 IU per day is the general tolerable upper intake level, not a target dose, and clinicians may recommend different amounts for specific medical reasons. Speak with a doctor or qualified healthcare professional before supplementing, especially if you have HS, kidney disease, a calcium disorder, take regular medication, or are considering a high dose.

There is no single vitamin D supplement dose or blood target recommended for everyone with HS or autoimmune disease. A target of 80 to 100 ng/mL should not be pursued without specialist medical oversight, because this is above the range considered adequate for most people and may increase the risk of adverse effects. Vitamin D is not a cure for HS and should not replace care from a dermatologist or another qualified professional.

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