In recent decades, interest in vitamin D has increased exponentially, mainly due to the fact that its deficiency has been associated with multiple diseases and that there appears to be a high deficiency of this micronutrient in the general population.
Since the identification of the chemical structure of vitamin D in 1930, there have been important advances in research into its functions in the body. Initially, studies focused on the role of this compound and its metabolites in calcium homeostasis and bone metabolism.
Later, with the discovery of 25-hydroxyvitamin D (25(OH)D), in 1968, and 1,25-hydroxyvitamin D (1,25(OH)2D), later, research was expanded and They focused on the role it plays in the appearance of immunological diseases, infections, cancer and chronic non-communicable diseases (cardiovascular conditions, obesity, type 2 diabetes, etc.).
Currently, there is no doubt that vitamin D intervenes in the regulatory mechanisms of the immune system. In fact, its deficit is related to a worse prognosis for covid-19 infection.
Current epidemiological data show a deficiency of this vitamin in 40% of the European population, 24% of the American population and 37% of the Canadian population. These are really high figures that can cause some alarm. The population groups most at risk of developing hypovitaminosis are pregnant women, children, the elderly, obese people, individuals with darker skin tone and those with little exposure to sunlight.
Human beings can cover part of their vitamin D needs through cutaneous synthesis from cholesterol, if they are sufficiently exposed to sunlight. It is difficult to specify the minimum recommended time, since it depends on factors such as the season of the year, time of day, geographical latitude, age or skin phototype.
A panel of experts from the Spanish Society for Bone Research and Mineral Metabolism recommends daily sun exposure of 15 minutes on the face and arms for the Caucasian population between the months of March and October. In elderly people and patients with osteoporosis, the advice is to extend it to 30 minutes. In both cases, a protection factor between 15 and 30 must be used, depending on the latitude and the intensity of UV (ultraviolet) radiation.
However, the contribution through diet is also necessary. Good dietary sources of this substance include oily fish (especially salmon and trout), non-skimmed dairy products, and margarines and enriched vegetable drinks.
And what is the reason for the growing vitamin D deficiency? Factors such as the increasingly frequent use of sunscreen or the downward trend in the consumption of foods rich in fat could contribute to this situation.
Currently, to evaluate vitamin D levels, the serum concentration of 25(OH)D is determined, although the results may vary depending on the analytical method.
In general, it is considered that values greater than 20 nanograms per milliliter (ng/mL) are optimal for the general population, and greater than 30 ng/mL for people over 65 years of age, patients with bone conditions or chronic pharmacological treatments (corticosteroids). , anticonvulsants...).
Values between 12 and 20 ng/mL are considered insufficient, and values below 12 ng/mL are considered deficient. There is also clear concern about the risks of hypervitaminosis D, which is associated with 25(OH)D levels above 100 ng/mL.
The need or convenience of prescribing vitamin D supplements to people who have adequate serum 25(OH)D levels, with the aim of improving their immune response, is a controversial issue.
In this sense, a recent meta-analysis evaluated supplementation of 1,000-2,000 international units (IU) per day in healthy individuals and concluded that it did not lead to significant improvements in immune system function. It was also not useful as a prevention tool for acute respiratory diseases, flu, covid-19 infection, etc.
However, other authors have observed positive effects of this intervention in individuals with respiratory diseases, especially in those with vitamin deficiency. There are also contradictory results about its benefits in patients with metabolic diseases and neurodegenerative conditions.
The intake of vitamin D present in foods is unlikely to cause problems, but indiscriminate supplementation, without there being a deficiency to justify it, can generate chronic toxicity. Thus, for example, the administration of vitamin D supplements in doses higher than 4,000 IU/day for prolonged periods could raise the serum concentration of 25(OH)D to values higher than 50 ng/ml, with the consequent risk of hypervitaminosis. .
The most characteristic manifestation of hypervitaminosis D is hypercalcemia, characterized by the appearance of gastrointestinal symptoms (anorexia, nausea, vomiting, constipation...), weakness and fatigue. In more severe cases, it can cause polyuria (excess urine production), polydipsia (abnormal increase in thirst), kidney failure, ectopic calcifications (out of place), depression, confusion, bone pain, fractures and kidney stones. .
In recent years, due to the increased consumption of supplements, cases of toxicity have increased significantly. Thus, the report from the National Toxicity Data System of the United States indicates that this overexposure to vitamin D has caused an increase in cases of hypervitaminosis, going from an annual average of 196 in the period 2000-2005 to 4,535 in the five-year period. following.
In conclusion, interest in vitamin D has increased significantly due to its association with multiple diseases and a possible, but perhaps not well established, deficiency in the population. However, the effects of supplementation in people who are not deficient are by no means conclusive.
There is evidence of its effectiveness in reducing the severity of respiratory diseases in people with a deficiency of the micronutrient in question. Hypervitaminosis D, resulting from indiscriminate supplementation, is a real risk and can be dangerous, causing hypercalcemia and other health problems.
Therefore, it is essential to approach this issue with caution, always acting based on scientific evidence and with caution when taking or recommending a vitamin D supplement.
With current scientific evidence, the myth of supervitamin D falls and the reality that more research is needed prevails.
This article was originally published on The Conversation.
M. Carmen Vidal Carou is Professor of Nutrition and Bromatology at the Food Campus of Torribera, at the University of Barcelona; Maria Teresa Veciana Nogués is Full Professor of Nutrition and Bromatology at the Torribera Nutrition Campus, at the University of Barcelona; Natalia Toro Funes is Professor of Nutrition and Bromatology at the University of Barcelona; and Sònia Sánchez Pérez is a Juan de la Cierva postdoctoral researcher and PhD in Food and Nutrition at the Torribera Food Campus, at the University of Barcelona.
