VITAMIN D

THE SUNSHINE HORMONE

The truth about vitamin D and the secrets of safe supplementation

INTRODUCTION. A GREAT MISUNDERSTANDING

Most of us grew up believing that vitamin D is simply another dietary supplement meant to prevent rickets in children. However, this is a fundamental mistake.

Vitamin D is not actually a vitamin, but a powerful steroid hormone—more precisely, a seco-steroid—that controls between three and ten percent of our genome. The vitamin D receptor is found in almost every cell of the human body, which means it affects virtually every system in the body.

Today, we are living through a global pandemic of deficiency of this hormone. It is estimated to affect more than one billion people worldwide. This article will guide the reader through the maze of myths surrounding vitamin D, explain why official recommendations can be drastically underestimated, and show how to safely benefit from the knowledge of pioneers such as Dr. Cícero Coimbra.

WHAT IS VITAMIN D

Vitamin D, despite its common name, is not actually a vitamin. It is a powerful steroid hormone, more precisely a seco-steroid. This distinction is of fundamental importance. Vitamins are substances that the body needs in small amounts but cannot produce on its own. A hormone, on the other hand, is a signaling molecule produced by the body to communicate with cells and regulate their behavior.

The classification of vitamin D as a vitamin is largely the result of a historical mistake from the early twentieth century. At that time, a substance preventing rickets was discovered in food products such as cod liver oil. It was not yet known that the human body can synthesize it on its own under the influence of sunlight.

The biological role of vitamin D extends far beyond bone health. The active form of this hormone, called calcitriol, acts as a molecular switch regulating the expression of three to ten percent of the human genome. This means it affects the functioning of approximately nine hundred to as many as three thousand genes. Vitamin D receptors, called VDRs, are found in the nuclei of nearly all cells in the human body.

As a result, vitamin D plays a key role in regulating the immune, cardiovascular, and nervous systems. Among other things, it supports the production of natural antibiotics in the body, such as cathelicidin, which effectively combat viruses and bacteria.

From an evolutionary perspective, vitamin D also acts as an environmental signal that informs the body about resource availability and seasonal changes. According to the Human Hibernation Syndrome theory, low levels of vitamin D3 resulting from lack of sun exposure send a signal to our DNA: winter and famine are coming.

In response, the body activates survival mode. This manifests as increased fat storage, greater appetite for carbohydrates and fats, and an overall slowing of metabolism. A state resembling depression or chronic fatigue often also occurs, limiting physical activity during periods of energy shortage.

At the same time, the body may enter a state known as incomplete repair syndrome. In this mode, tissues and bones are repaired only to a minimal extent in order to preserve mineral resources until favorable environmental conditions return.

The evolution of human skin color was also strongly linked to vitamin D production. Populations that migrated north gradually lost their dark skin pigment to enable efficient vitamin D synthesis under weaker sunlight.

THE VITAMIN D HORMONE FACTORY. HOW IT WORKS

Understanding vitamin D metabolism is key to its safe use. The entire process can be compared to preparing a meal.

First, we have raw meat in the freezer. In our body, its equivalent is the cholesterol found in the skin, namely 7-dehydrocholesterol.

Next comes defrosting. In biology, this means the moment when UVB radiation hits the skin and converts cholesterol into cholecalciferol, or actual vitamin D3.

The next stage is „grinding the meat.” In the body, this takes place in the liver, where vitamin D3 is converted into calcifediol, denoted as 25(OH) D. This is the form that is tested in the blood.

The final stage can be compared to frying in a pan. In the kidneys and other tissues, calcitriol is produced—an active hormone that sends instructions to cells throughout the body.

It is worth remembering that vitamin D2, which is of plant origin, is much less effective than natural human vitamin D3. The body must make an additional effort to process it, and its biological activity is up to three times lower.

HOW VITAMIN D WORKS IN THE BODY

The active form of vitamin D, calcitriol, acts as a powerful regulator of cellular functions. Since vitamin D receptors are found in nearly every cell in the body, its influence extends to many biological systems.

One of the most important areas of action is the immune system. Vitamin D acts as an immunomodulator that affects both innate and acquired immunity. It stimulates the production of antimicrobial peptides, such as cathelicidin and defensins, which help fight bacteria, viruses, and fungi.

At the same time, vitamin D helps prevent autoimmune reactions of the immune system. It supports the production of regulatory T cells, which act as a biological brake on immune responses, preventing the body from attacking its own tissues.

Vitamin D also plays an important role in maintaining healthy bones and muscles. It is essential for the proper absorption of calcium and phosphorus in the intestines. It stimulates the activity of osteoblasts, the cells responsible for bone formation, and prevents excessive activity of the parathyroid glands, which could lead to weakening of the bone structure.

Its effects also extend to the muscular system. Vitamin D affects muscle strength and mass, improving balance and reaction time. This is particularly important in preventing falls among older adults.

No less important is the effect of vitamin D on the nervous system. This hormone acts as a neurosteroid, participating in brain development and protecting neurons from damage. It regulates the levels of neurotransmitters such as serotonin, dopamine, and adrenaline, which directly affects mood and cognitive functions.

WHY DO MOST PEOPLE HAVE A DEFICIENCY

Modern science indicates that vitamin D deficiency is a global issue. It is estimated to affect over one billion people worldwide. The causes of this phenomenon are complex and result from both lifestyle changes and environmental factors.

Modern lifestyles play the most important role. Most people spend a significant part of the day indoors, working in offices or using electronic devices. As a result, the skin has very limited exposure to UVB radiation.

An additional factor is the widespread use of sunscreen creams, which can block vitamin D synthesis by as much as over ninety percent. Added to this is the obesity epidemic, because vitamin D dissolves in fatty tissue and may become trapped there.

The aging of societies is also significant. With age, the skin loses its ability to produce vitamin D efficiently, and in older people the effectiveness of this process may decline to as little as about one quarter of the level observed in young people.

THE HUMAN HIBERNATION SYNDROME

Why does a lack of sunlight make us gain weight and get sick more often?

Jeff Bowles proposed an interesting theory called the Human Hibernation Syndrome. According to it, a drop in vitamin D levels is an evolutionary signal to the body: winter and a period of food scarcity are coming.

In such a situation, the body begins to behave as if it were preparing to survive a difficult period.

The body begins to store fat in order to survive periods of food scarcity, which may be one of the factors behind the modern obesity epidemic.

Drowsiness and a drop in energy also appear, which can be interpreted as an energy-saving mechanism.

Additionally, the body enters the so-called Incomplete Repair Syndrome, in which it performs only minimal tissue repairs in order to conserve the mineral resources needed to survive the „winter.”.

According to this concept, many chronic injuries and inflammatory conditions subside only after higher doses of vitamin D3 are administered, which signal to the body the arrival of biological summer.

IMPACT ON CHRONIC DISEASES

Vitamin D deficiency is sometimes referred to as hormonal hibernation syndrome. It puts the body into a state of resource conservation and limited tissue regeneration. The long-term persistence of such a state promotes the development of many lifestyle-related diseases.

In autoimmune diseases, high doses of vitamin D, used among others in the Coimbra Protocol, demonstrate very high effectiveness in halting the progression of multiple sclerosis. Similar mechanisms of action are observed in lupus, psoriasis, and rheumatoid arthritis.

Vitamin D may also play an important role in cancer prevention. It promotes apoptosis, i.e. the programmed death of cancer cells, inhibits angiogenesis, and hinders the formation of metastases. Epidemiological studies have shown that an optimal level of vitamin D in the blood may significantly reduce the risk of certain cancers.

In the context of diabetes, vitamin D protects pancreatic beta cells and improves cellular sensitivity to insulin. It also affects the regulation of blood pressure by inhibiting the RAAS system responsible for the development of hypertension.

THE SUNSCREEN TRAP AND THE MYTH OF SAFETY

For decades, dermatologists have repeated one phrase: „avoid the sun.” However, the effect of this advice has proven paradoxical. On the one hand, it has led to widespread vitamin D deficiency in the population, and on the other, it has not stopped the rise in melanoma cases.

Sunscreen products can block vitamin D production in the skin by as much as ninety-five to ninety-eight percent. At the same time, they do not always effectively protect against melanoma, because they give people a false sense of safety. As a result, many people stay in the sun much longer than they would without protection, while failing to develop the natural protective barrier of a gradually developing tan.

So how can you use the sun safely? It is best to expose yourself to sunlight around midday, roughly between eleven and three, when UVB radiation is strongest. In many cases, a few to several minutes without sunscreen are enough, until the skin becomes slightly pink. It is also worth remembering that glass blocks UVB radiation, so sitting by a window does not lead to vitamin D production.

ESSENTIAL PARTNERS – VITAMIN K2 AND MAGNESIUM

Supplementing with vitamin D3 alone is a serious mistake. This hormone needs two key partners to function properly.

The first of these is vitamin K2, especially in the MK-7 form. Vitamin D increases calcium absorption from the intestines, but it is vitamin K2 that determines where calcium will ultimately be used. It activates proteins such as osteocalcin and MGP, which remove calcium from the arteries and direct it to the bones and teeth. Without an adequate amount of vitamin K2, there is a risk of blood vessel calcification. It is generally recommended to take at least one hundred micrograms of vitamin K2 for every ten thousand units of vitamin D3.

The second key element is magnesium. It is essential for the activation of vitamin D in the body. Without adequate magnesium levels, vitamin D remains in an inactive form, which may lead to symptoms resembling toxicity, even though the actual problem is a deficiency of this mineral.

DIAGNOSTICS – DON'T BE MISLED BY TESTS

In vitamin D diagnostics, the proper choice of laboratory test is crucial. At the laboratory, one should always request measurement of the 25(OH) D level, i.e., calcifediol. This is the storage form of vitamin D and the best indicator of its level in the body.

However, the active form of the hormone, i.e., 1,25(OH)₂D₃, should not be tested for the purpose of diagnosing deficiency. Its level may be high even when the body's vitamin D stores are very low.

Interpreting the results also requires caution. Many laboratories consider a level of thirty nanograms per milliliter to be normal. However, for optimal health and protection against cancer, it is recommended to aim for a level of fifty to eighty nanograms per milliliter. In therapeutic protocols, this level may be even higher, naturally under close medical supervision.

A particularly important indicator when using higher doses is the level of the PTH hormone, or parathyroid hormone. The goal of therapy is to lower it to the lower limit of the normal range, which means that the body has been adequately saturated with vitamin D.

HIGH-DOSE PROTOCOL AND SAFETY

People struggling with chronic diseases often discover that standard doses of vitamin D are insufficient. Recommendations of six hundred to two thousand international units per day are usually unable to overcome the body's resistance to this hormone.

For a healthy adult, a dose of up to ten thousand international units per day is commonly considered safe. Interestingly, our skin can produce a similar amount of vitamin D in a single day during sun exposure.

However, in the case of therapeutic doses, which may be as high as approximately one thousand international units per kilogram of body weight, strict safety guidelines must be followed. This is intended to prevent hypercalcemia, or excess calcium in the blood.

The basic safety guidelines described in Dr. Coimbra's protocol primarily include a low-calcium diet. This means completely eliminating dairy products, including milk, cheese, and yogurt, as well as calcium-fortified products.

The second pillar is proper hydration. It is recommended to drink at least two and a half litres of fluids per day so that the kidneys can effectively remove excess calcium from the body.

The third element is physical activity. Walking or strength exercises help direct calcium to the bones instead of allowing it to circulate in the bloodstream.

DOSAGE

The issue of vitamin D dosage has sparked considerable controversy for years. Official recommendations from many health institutions are based on doses established solely to prevent rickets.

In many countries, the recommended daily intake ranges from four hundred to eight hundred international units. However, many experts believe that such doses are insufficient to achieve optimal vitamin D levels in the blood.

An increasing number of specialists indicate that a dose of up to ten thousand international units per day may be safe for healthy adults, as it corresponds to the amount the body can produce during brief exposure to sunlight.

In therapeutic protocols used in the treatment of chronic diseases, doses may be significantly higher. In such cases, however, supplementation requires regular laboratory tests and strict medical supervision.

SAFETY

The main risk associated with excessive vitamin D supplementation is hypercalcemia, i.e. an excess of calcium in the blood. Vitamin D increases the intestines' ability to absorb calcium and, in some situations, may also lead to its release from bones.

Symptoms of hypercalcemia may include nausea, vomiting, constipation, fatigue, and heart rhythm disturbances. In severe cases, kidney damage, kidney stones, and even coma may occur.

Therefore, when using higher doses, regular monitoring of vitamin D levels, calcium, and other laboratory parameters is necessary.

MOST COMMON MISTAKES

One of the most common mistakes is supplementing vitamin D without the appropriate cofactors, especially without vitamin K2 and magnesium. In such a situation, increased calcium absorption may lead to its deposition in undesirable places.

Another common mistake is the fear of doses greater than a few hundred international units. In reality, the human body is adapted to much larger amounts of vitamin D, which are naturally produced during sun exposure.

Another problem is the incorrect interpretation of laboratory tests. Often, the wrong form of vitamin D is tested, and the results are interpreted according to underestimated reference ranges.

Other mistakes include taking vitamin D without fat in the meal, excessive calcium intake at high doses, and having follow-up tests too infrequently.

Regular monitoring of vitamin D, calcium, and other metabolic indicators helps avoid most potential problems and makes supplementation a safe tool for supporting health.

SUMMARY. YOUR HEALTH IS IN YOUR HANDS

Vitamin D is sometimes called the cheapest life insurance policy. It is easily available, inexpensive, and has a huge impact on how the body functions.

At the same time, knowledge about it comes with responsibility. Supplementing with very high doses should not be done without monitoring kidney function and without consulting a doctor who understands modern hormone science.

Returning to natural contact with sunlight, conscious supplementation, and appropriate diagnostics can help the body stop functioning in biological winter mode.

Therefore, it is worth ensuring that the body never receives the signal that a time of scarcity and hibernation is approaching.

BIBLIOGRAPHY

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Nabil I.K. Vitamin D receptor and hypertension. 2024. 

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Ekmekcioglu C. Optimal 25(OH) D levels for disease prevention. 2025. 

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