In November 2025, I published a book I authored entitled “Innate Immunity: The Great Neglected Factor During the Covid-19 Pandemic – Unjustifiable Disregard for Vitamin D3 Homeostasis.”
The significance of vitamin D3 levels in the population’s blood is not limited to Covid-19, but also concerns the onset (and course of clinical progression) of a large number of other diseases—listed in the book’s Supplementary Bibliography, pages 165–208—namely infectious diseases (not just those of the respiratory system), autoimmune diseases, autism, psoriasis and others. The action of vitamin D3—in promoting health and preventing disease—is therefore wide-ranging.
It is known that, to ensure the full strength of immune-system functions, achieving and maintaining an effective concentration of vitamin D3 (> 50 ng/mL) in everyone’s blood is essential. It is basic knowledge that vitamin D3 is indispensable for the prevention and, potentially, treatment of many human diseases (chapters 9 and 10 of the book and Supplementary Bibliography).
Although its existence was officially recognized only in 2010, humanity has been experiencing a pandemic of vitamin D3 deficiency for several decades. According to the World Health Organization, about 1.3 billion people worldwide (one in six) have a vitamin D3 deficiency. This is no small number compared with the 705 million people affected by Covid-19 (with just over 7 million deaths). Although anyone may be affected, vitamin D3 deficiency is most prevalent among older adults, Black people and people with obesity.
The main reasons why a large proportion of the world’s population (including Brazil’s) has developed vitamin D3 deficiency (< 20 ng/mL) or insufficiency (between 20 and 30 ng/mL) relate to three factors:
1) Vitamin D3 can only be obtained naturally through exposure of a large area of the body’s surface to sunlight (ultraviolet B rays), for an appropriate length of time and at the appropriate time of day. Over the past 50 years, much of Brazil’s population has moved from rural areas into cities. For example, Londrina had 212,902 residents in 1970, with 28% living in rural areas; by 2010, of its population of 506,701, only 2.6% lived in rural areas;
2) This development—the high concentration of people in urban centers—seen in all Brazilian states was accompanied by cultural habits adopted by almost all urban residents. They began spending most of their time indoors and exposing themselves to sunlight only occasionally, almost always wearing sunscreen (which prevents ultraviolet B rays from reaching the skin, specifically the lower layers of the epidermis, to promote the formation of previtamin D3);
3) At the same time, most people do not receive guidance from their physicians or public health administrators on properly supplementing vitamin D3 orally (that is, in appropriate doses and regimens).
Because a large share of the population has vitamin D3 deficiency or insufficiency, the diseases associated with this deficit have become more frequent and more severe. Cases of rickets have reappeared in children, and osteoporosis has become more common among older adults. Globally, 15.7% of children have blood vitamin D3 levels below 12 ng/mL, a rate that reaches 71.8% in countries east of the Mediterranean Sea and 40% to 80% in South Asia. Osteoporosis currently affects around 500 million people worldwide and is highly underdiagnosed. Data on vitamin D3 deficiency and insufficiency in Brazil and worldwide (including among health professionals) can be found in chapters 4 and 5 of the book.
As vitamin D3, among its dozens of biological functions (almost all human cells have a vitamin D receptor), plays a significant role in the immune system—in both innate and acquired immunity—protecting humans against many diseases, various health problems (beyond rickets and osteoporosis) associated with its deficiency have become more frequent and more severe.
As already mentioned, the Covid-19 pandemic is only one example of what has recently occurred in Brazil and most countries around the world, with large numbers of cases and deaths. The high prevalence of vitamin D3 deficiency in the population contributed significantly to these outcomes, a fact whose importance was recognized only by researchers who—like me—studied this association in depth. It was not coincidental, as some “argue,” but indeed causal—at least, and indisputably, in relation to Covid-19 prevention.
The expression “innate immunity” was neither written nor spoken (except two or three times in passing) during the Covid-19 pandemic by commentators and analysts in the traditional media (newspapers, magazines and radio and television broadcasters) who sought to identify the factors involved in the causes and consequences of that pandemic.
Repeated outbreaks of acute respiratory viral infections (and their complications, including severe acute respiratory syndrome, or SARS, with significant numbers of deaths) occur in Brazil and worldwide—as we are witnessing here this autumn (the driest season of the year, favorable to the spread of respiratory infections). Such outbreaks are caused not only by influenza viruses and respiratory syncytial virus (the only ones for which vaccines are available), but by hundreds of types and serotypes of so-called “respiratory viruses,” including rhinoviruses (30% of current SARS cases), adenoviruses, pneumoviruses and others, for which there are no vaccines.
The available alternative (in addition to the need for broad use of the two existing vaccines) to reduce the incidence and complications of the many acute respiratory viral infections is to adopt measures aimed at correcting low blood concentrations of vitamin D3—observed in a large share of the population (a pandemic of vitamin D3 deficiency)—through a low-cost, easily implemented procedure to be carried out by health professionals, particularly physicians trained to provide this type of care at basic health units within Brazil’s public health system (SUS). If there are insufficient resources to cover the whole population with this proposal (an objection that will almost certainly be raised), priority could initially be given to those most vulnerable or exposed to infection, including older adults, people living in nursing or retirement homes, individuals with obesity (morbid or otherwise), and those with diseases or clinical conditions that suppress immune function, whether innate or acquired (including cancer patients undergoing treatment, organ-transplant recipients and people taking immunosuppressive medication).
Putting this program into practice requires only political will from government leaders, together with health administrators who have appropriate scientific training.
In the book, we describe our personal experience supplementing vitamin D3 in 97 older adults living at the São Vicente de Paulo nursing home in Londrina, between August 2020 and September 2021 during the Covid-19 pandemic. There were no deaths among the older residents who remained at the São Vicente de Paulo home during this period and took vitamin D3 under medical supervision and monitoring. It is known that the Covid-19 fatality rate in Brazilian nursing homes during the pandemic exceeded 15%, and there is information that in 2020 some 24,500 older adults living in nursing homes in São Paulo state died, out of a total of 60,000 older adults cared for in nursing homes in our country that year.
It is important to note that within Brazil’s so-called medical-scientific community, there is intense controversy—if not complete “disbelief” or “indifference”—about the results of using vitamin D3 to treat Covid-19 in people deficient in this hormone. As documented in the book, a large number of studies on treating Covid-19 through oral vitamin D3 (cholecalciferol) administration show unfavorable or inconclusive results, invariably because of methodological flaws (insufficient vitamin D3 doses and inadequate regimens, treatment started too late, very small samples, and so on). To cite one example, in a study conducted in the intensive care unit of the Hospital das Clínicas at the University of São Paulo Medical School, the authors concluded that a single oral “high dose” (200,000 IU) of vitamin D3 (cholecalciferol), given on average on the tenth day of hospitalization, brought no benefit to patients with low blood vitamin D3 concentrations. (This study—considered “exemplary”—is repeatedly included in published meta-analyses of vitamin D3 treatment for Covid-19.) Specialized literature recognizes a single high dose of vitamin D3 for treating Covid-19 at the appropriate time as 600,000 IU. It is already known that the biological activity of vitamin D3 (in the form of cholecalciferol), when administered orally as a high single dose, begins no sooner than seven to ten days after ingestion by healthy people, as cholecalciferol must be converted in the kidneys into calcitriol (the active form of vitamin D3), after passing through the liver, where it is converted into another form of vitamin D3 not yet biologically active, called calcidiol or calcifediol (the form of vitamin D3 circulating in the blood and detected in laboratory tests). By the tenth day of hospitalization, when the “high dose” of cholecalciferol was given in the study cited (conducted in the intensive care unit at the Hospital das Clínicas of the University of São Paulo Medical School), the patients were certainly already in a clinical condition in which no treatment could produce a favorable result.
Our analysis in chapter 10 of the book clearly demonstrates the highly beneficial effect of Covid-19 prophylaxis carried out by administering appropriate oral doses (using correct regimens) of cholecalciferol, capable of raising blood vitamin D3 concentrations to protective levels (ideally between 50 and 80 ng/mL) before infection occurs (a preventive effect).
Maintaining these elevated blood concentrations of vitamin D3 (between 50 and 80 ng/mL) has also been scientifically shown to prevent various other types of infections and noninfectious diseases.
In our view, public health authorities urgently need to adopt measures that promote vitamin D3 homeostasis in the population. In other words, programs must be implemented immediately to give people access to an additional (natural) resource that they currently lack and that can help them prevent or confront the health problems mentioned above.
Source: brasil247.com by Dr. José Luís da Silveira Baldy
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