Vitamin D, often called the “sunshine vitamin,” goes far beyond its traditional role in bone health. It acts as a powerful hormone, regulating more than 200 genes in the body and directly impacting the immune system, metabolism, cardiovascular health, and even the prevention of autoimmune diseases and cancers. Still, most people are unaware of its true importance, and more concerning: they live with chronically low levels, often within “official reference values,” which many experts consider insufficient to ensure real health.
What Is Vitamin D? A Scientific and Updated View
Although classified as a vitamin, vitamin D acts in the body as a steroid prohormone, that is, a precursor substance of hormones that influence gene expression in more than 2000 human genes—about 10% of the genome. There are two main forms: vitamin D2 (ergocalciferol), of plant origin, and vitamin D3 (cholecalciferol), produced in the skin through sun exposure and also found in animal-based foods.
After being synthesized or ingested, vitamin D goes through two activation processes: the first occurs in the liver, where it is converted into 25-hydroxyvitamin D [25(OH)D], the form used to measure blood levels; the second in the kidneys, where it is transformed into 1,25-dihydroxyvitamin D (calcitriol)—its biologically active form. This molecule acts on various tissues, including bones, brain, immune system, heart, and even cancer cells.
Moreover, vitamin D influences calcium and phosphorus absorption, regulates cell growth, neuromuscular function, and inflammatory balance. Its deficiency, therefore, compromises not only bones—but the entire metabolism of the body.
How Is Vitamin D Synthesized by the Body?
The main way the human body obtains vitamin D is through cutaneous synthesis, a highly efficient biochemical process—but one that depends on very specific factors. It begins with skin exposure to ultraviolet B (UVB) radiation, which acts on cholesterol present in the epidermis, converting 7-dehydrocholesterol into pre-vitamin D3. This molecule then undergoes a thermal rearrangement and becomes vitamin D3 (cholecalciferol), which will later be activated in the liver and kidneys.
However, this synthesis depends on variables that can drastically limit its effectiveness:
- Time of day: Optimal production occurs between 10 a.m. and 3 p.m., when UVB radiation is most intense.
- Skin color: People with darker skin have higher amounts of melanin, which acts as a barrier to UVB radiation, reducing production.
- Age: With aging, the amount of 7-dehydrocholesterol in the skin decreases, reducing vitamin synthesis.
- Sunscreen use: Sunscreens with SPF 15 or higher can block up to 99% of vitamin D production in the skin.
- Latitude and season: Regions above 35 degrees latitude (North or South) have low UVB radiation during autumn and winter, making adequate production nearly impossible.
- Pollution and clothing: Urban environments with high pollution or excessive clothing further hinder effective sun exposure.
This set of factors explains why, even in tropical countries like Brazil, a significant portion of the population has vitamin D deficiency—even when exposed to the sun daily.
Natural Sources of Vitamin D in Food
Although vitamin D can be obtained through diet, natural foods rich in this nutrient are relatively scarce. Most are of animal origin, especially those that contain fat, since vitamin D is fat-soluble. This means its absorption depends on the presence of lipids in the meal.
Check out the main food sources of vitamin D3 (cholecalciferol), the most bioavailable form for the human body:
| Food | Quantity (per 100 g) | Vitamin D (IU) |
|---|---|---|
| Cod liver oil | 1 tablespoon | ~10.000 UI |
| Sardines (canned or grilled) | 100 g | 300–400 UI |
| Wild salmon | 100 g | 600–1000 UI |
| Beef liver | 100 g | 50–100 UI |
| Egg yolk | 1 unit | 20–40 UI |
| Mushrooms (UV-exposed) | 100 g | até 400 UI (D2) |
| Whole milk (fortified) | 1 glass (200 ml) | 100–150 UI |
It is worth noting that vitamin D2 (ergocalciferol), found in mushrooms and some plant foods, is less efficient at raising serum 25(OH)D levels compared with vitamin D3. In addition, cooking, storage, and industrial processing methods can reduce the nutrient’s concentration in foods.
Therefore, although diet contributes to vitamin D intake, it is not sufficient on its own to reach ideal levels—especially those recommended by more recent studies, which point to maintaining concentrations above 60–80 ng/mL for significant immunological and metabolic benefits.
Vitamin D Supplementation: Doses, Forms, and Care
Given the difficulty of achieving ideal vitamin D levels through diet and sun exposure alone, supplementation has become an essential strategy for much of the population. Supplementation can be taken orally (capsules, drops, or tablets) or by injection, with the oral route being the most common and accessible.
Doses vary according to age, weight, sun exposure, pre-existing conditions, and serum 25(OH)D levels. Below is a general estimate based on updated medical recommendations:
| Group | Recommended daily dose |
|---|---|
| Healthy adults | 2.000 a 4.000 UI |
| Older adults (> 65 years) | 4.000 a 6.000 UI |
| People with moderate deficiency | 10,000 IU for 8 to 12 weeks |
| Individuals with obesity or malabsorption | 10,000 to 20,000 IU daily |
| Maintenance after repletion | 5,000 IU for an indefinite period |
- ⚠️ Atenção: A dose segura máxima, segundo a Endocrine Society, pode chegar a 10.000 UI/dia. Porém, o ideal é sempre suplementar sob orientação médica, com acompanhamento de exames laboratoriais para evitar toxicidade, embora essa condição seja extremamente rara e geralmente ligada a uso crônico e indiscriminado.
Another essential point is the form of vitamin D. Vitamin D3 (cholecalciferol) is more effective than D2 (ergocalciferol), with a longer half-life and a better ability to raise blood levels. It is also important to take it with healthy fats (such as olive oil or omega-3) to ensure absorption, since it is a fat-soluble vitamin.
Vitamin D Deficiency: Causes, Symptoms, and Consequences in the Body
Vitamin D deficiency is considered one of the most prevalent nutritional deficiencies worldwide, affecting millions of people of all ages—even in sunny countries. The problem is compounded by the fact that symptoms are often silent or mistaken for other conditions, delaying diagnosis and treatment.
Main causes of deficiency
- Lack of adequate sun exposure
- Excessive use of sunscreen or clothing that covers the skin
- Dark skin, which hinders vitamin D synthesis
- Natural aging
- Obesity (vitamin D becomes “sequestered” in adipose tissue)
- Intestinal diseases (such as celiac disease, Crohn’s, or bariatric surgery)
- Chronic use of medications (such as anticonvulsants, corticosteroids, or orlistat)
Most common signs and symptoms
- Constant fatigue and lack of energy
- Muscle aches and weakness
- Hair loss
- Fragile bones with increased fracture risk
- Frequent infections (colds, flu)
- Sadness, irritability, or depressive symptoms
- Impaired concentration and memory
Consequences in the body
Prolonged vitamin D deficiency affects the body systemically. In the short term, it compromises the immune response, muscle function, and the balance of calcium and phosphorus in the blood. In the long term, it may increase the risk of serious diseases such as:
- Osteopenia and osteoporosis
- Type 2 diabetes
- Hypertension
- Autoimmune diseases (lupus, multiple sclerosis)
- Alzheimer’s and neurodegenerative diseases
- Cancers (breast, prostate, colon)
🧠 Curiosidade científica: Estudos mostram que níveis adequados de vitamina D podem reduzir em até 50% o risco de infecções respiratórias e regular a atividade de linfócitos T — células essenciais do sistema imune.
Vitamin D and the Immune System: The Forgotten Link of Natural Immunity
Vitamin D is not merely a supporting actor in the immune system—it is a protagonist. It acts as an immunomodulator, regulating both innate and adaptive immunity. Its receptors (VDR) are present in virtually all immune cells: monocytes, macrophages, dendritic cells, and T and B lymphocytes.
How vitamin D strengthens the immune system:
- Stimulates the production of antimicrobial peptides, such as cathelicidin, which rapidly destroys viruses, bacteria, and fungi.
- Decreases low-grade chronic inflammation, common in autoimmune and metabolic diseases.
- Reduces the exaggerated immune response (cytokine storm), which can be fatal in severe viral infections.
- Promotes balance between Th1 and Th2 lymphocytes, helping prevent allergies and autoimmune responses.
During the COVID-19 pandemic, several studies associated low vitamin D levels with worse clinical outcomes, longer hospitalizations, and higher mortality. Although vitamin D does not prevent infections on its own, it modulates the severity of the body’s response and may improve recovery.
Populations with deficiency tend to get sick more:
- Children with low immunity and frequent respiratory infections
- Older adults, the group with higher mortality from flu and pneumonias
- Immunocompromised individuals, such as transplant recipients or people with cancer
- People with autoimmune diseases (vitiligo, Hashimoto’s thyroiditis, lupus)
🔬 Dado relevante: Um estudo publicado na revista BMJ revelou que a suplementação de vitamina D reduziu em até 70% o risco de infecções respiratórias agudas em pessoas com deficiência grave.
Ideal Vitamin D Levels: Why Are the Reference Ranges So Low?
Most laboratories and public health agencies define a “sufficient” vitamin D (25(OH)D) level as between 20 to 30 ng/mL. However, many independent physicians and researchers warn that these values are extremely conservative and were established exclusively based on bone health—ignoring vitamin D’s systemic and immunological effects.
Values advocated by independent experts:
- Insufficient: below 40 ng/mL
- Ideal for immunity and chronic disease prevention: between 60 and 100 ng/mL
- Optimal for autoimmune, oncology, or chronic-disease patients: between 80 and 120 ng/mL
- Potentially toxic: above 150 ng/mL for a prolonged period
These values are not mere guesswork. Population and clinical studies show that people with levels above 60 ng/mL have a lower incidence of:
- Viral and bacterial infections
- Autoimmune diseases (such as multiple sclerosis and rheumatoid arthritis)
- Hypertension, type 2 diabetes, and insulin resistance
- Certain cancers, especially breast, colon, and prostate
Why do official levels remain low?
There is growing criticism that lower guidelines favor the rise of silent chronic diseases, generating a lucrative cycle of ongoing medication. In addition, current recommendations were based on older studies, overlooking recent advances in endocrinology and nutritional immunology.
⚠️ Atenção importante: Ter valores “normais” no exame laboratorial não significa estar saudável. O ideal é buscar níveis funcionais — não apenas evitar o mínimo necessário para evitar o raquitismo.
High-Dose Vitamin D: Myths, Real Risks, and Monitoring
The notion that vitamin D can cause toxicity at high doses is one of the greatest fears associated with supplementation, but also one of the most misunderstood. In clinical practice, toxicity cases are extremely rare and usually occur after prolonged use without laboratory monitoring, with doses far higher than those recommended by experienced physicians.
What is considered a “high dose”?
- For most people, doses above 10,000 IU per day are considered high.
- In controlled therapeutic protocols, such as the Coimbra Protocol (used for autoimmune diseases), doses may exceed 50,000 IU/day, with individualized adjustments and rigorous monitoring of calcium, creatinine, urea, and parathyroid hormone (PTH).
The real risk of excessive vitamin D:
The main risk of hypervitaminosis D is hypercalcemia—excess calcium in the blood, which can lead to symptoms such as:
- Nausea and vomiting
- Muscle weakness
- Mental confusion
- Kidney stones
- Dehydration
However, these symptoms usually appear only with levels above 150–200 ng/mL for a prolonged period without supervision and with concomitantly high calcium intake.
What the most recent science shows:
Studies show that, to cause toxicity, one would need to maintain a daily intake of 40,000 to 100,000 IU for several months without interruption—far beyond usual clinical practice.
✅ Conclusão segura: Suplementar vitamina D em doses de 4.000 a 10.000 UI por dia é considerado seguro para adultos saudáveis, desde que acompanhado por um profissional e com exames periódicos.
Conclusion:
Magnesium is much more than a simple mineral—it is a true pillar of physical and mental health. Involved in hundreds of bodily functions, adequate levels are essential for a healthy heart, proper muscle function, balanced brain activity, and good sleep.
Unfortunately, magnesium deficiency has become common in modern life—due to poor diet, chronic stress, or prolonged medication use. Knowing the signs of deficiency, identifying rich food sources, and understanding when supplementation is needed can make all the difference to your quality of life.
The safest and most effective path is to adopt a balanced diet rich in vegetables, seeds, and whole foods—and seek professional guidance when needed. Small changes can bring big results.
✨ And you, have you checked your magnesium levels?If you’ve been feeling tired, irritable, having trouble sleeping, or experiencing frequent cramps, your body may be asking for more of this essential mineral. Start today by making small changes to your diet and, if necessary, talk to a trusted nutritionist or doctor.
Your health will thank you—and your body will feel the difference!
Why Is Vitamin D the Most Underestimated Nutrient in Modern Health?
Vitamin D transcends its classic role in bone health. It is a true orchestrator of bodily balance, influencing immunity, metabolism, hormonal function, mental health, and the prevention of chronic diseases. Even so, it remains neglected by official guidelines, underdosed in treatments, and misunderstood by much of the population—and even by many health professionals.
We live in a scenario where people have tests “within normal range” yet continue to get sick with recurrent colds, chronic fatigue, depression, muscle pain, and silent autoimmune diseases. In many such cases, vitamin D deficiency is a key missing piece of the puzzle.
The good news? Treating deficiency is simple, accessible, and can transform health. Mindful sun exposure, strategic nutrition, and guided supplementation can restore balance and deliver real quality of life—not just the absence of disease.
🌞 La vitamina D es gratuita, natural y vital. And perhaps, because it is so simple, it has been so easily forgotten.
What is the best time of day to get sun and produce vitamin D?
The best time to get sun exposure and stimulate vitamin D production is between 10 a.m. and 3 p.m., when UVB rays are most intense. This window favors more efficient cutaneous synthesis of vitamin D3.
How much sun per day is enough to synthesize vitamin D?
The required time varies by skin tone, location, and season. On average, 15–30 minutes per day are sufficient for fair skin. Darker skin may need up to 1 hour of daily exposure.
Who should not take high doses of vitamin D?
People with conditions such as sarcoidosis, hyperparathyroidism, chronic kidney disease, or elevated blood calcium (hypercalcemia) should avoid high doses without medical supervision.
Does vitamin D cause weight gain or weight loss?
Vitamin D neither causes weight gain nor weight loss directly, but adequate levels can improve metabolism, reduce inflammation, and modulate appetite-related hormones such as leptin.
Is it better to take vitamin D in capsules or drops?
Both forms are effective as long as they contain vitamin D3 (cholecalciferol) and are taken with a fat-containing meal. Drops offer greater dosing flexibility, while capsules are more convenient for ongoing use.
The choice depends on personal preference and professional guidance.
What’s the difference between vitamin D2 and D3?
Vitamin D3 (cholecalciferol) is of animal origin and is more effective at raising blood levels. Vitamin D2 (ergocalciferol) is plant-derived and has lower potency and stability.
Can I take vitamin D every day or do I need breaks?
Yes, vitamin D can be taken daily, especially at physiologic doses (2,000–5,000 IU/day). Breaks are only indicated in high-dose protocols or per physician guidance based on labs.
The key is to maintain ideal serum levels over time with periodic monitoring.
References
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Níveis de vitamina D considerados suficientes
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Diretrizes clínicas Endocrine Society (adultos com obesidade ou má absorção)
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Relação entre vitamina D e imunidade (peptídeo antimicrobiano catelicidina)
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Meta-análises sobre infecções respiratórias
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Classificação de deficiência e insuficiência de vitamina D
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