To answer this question, we must first explain what this hormone is and what it is for.
Vitamin D (cholecalciferol) is present in some foods and can also be taken as a medicine or supplement. It is synthesized on the skin by ultraviolet B (UVB) rays from the sun. Among other functions, it reduces inflammation, since it inhibits the proliferation of cells that favor this process and enhances our immune system, which defends us from infections. Various studies have found that low levels of vitamin D are associated with a higher risk and worse clinical course of infections.
Multiple investigations suggest that a sufficient supply of vitamin D could protect against SARS-CoV-2 infection. They are ecological studies, which make global international comparisons with data aggregated by country. In other words, they don’t analyze individuals. This means that they only serve to suggest hypotheses, but not to prove them.
Observational studies predominate within individualized studies, where researchers simply collect data from thousands of participants. Another alternative would be randomized intervention trials, in which researchers intervene, randomly assigning different diets to participants. Random assignment ensures that equal groups are being compared.
In this context, ecological studies find that countries with lower average levels of vitamin D, or less exposure to UVB solar radiation, have presented higher mortality from covid-19. As they come from aggregated (ecological) data, they do not allow to prove it.
Prevention is not treating
Good observational studies, already individualized, have found that vitamin D-deficient groups had a higher risk of hospitalization and mortality from COVID-19. In addition, an inverse correlation has been found between vitamin D levels and the severity of the disease: the higher the vitamin D levels, the less severe. But correlation is not causation.
However, both observational studies and randomized intervention trials prior to the pandemic already showed that higher levels of vitamin D led to a lower risk of contracting viral respiratory tract infections. Regarding COVID-19, several observational studies have found that people with lower levels of vitamin D were more likely to have a poor prognosis for SARS-CoV-2 infection.
The biological plausibility of this association has not been questioned, since vitamin D influences the response to infections due to its immunomodulatory effect. These arguments are already proofs of causality, which could be corroborated through tests. Several randomized clinical trials are currently under way to assess the effect of adding vitamin D to the treatment of these patients.
The available scientific evidence suggests a possible preventive effect, but not that vitamin D is a valid treatment for COVID-19.
Solar exposition
As we explained in the book What do you eat? , few foods naturally contain significant amounts of vitamin D:
- Fatty fish (tuna, trout, salmon, mackerel) and fish liver oils.
- Beef liver, cheese and egg yolks have small amounts of vitamin D, mainly in the form of vitamin D3 and its metabolite 25 (OH) D3 (metabolites are substances produced during metabolism).
- Mushrooms and mushrooms provide varying amounts of vitamin D2. Exposing them to the sun before cooking increases these levels, which is why some of the mushrooms available on the market have been previously treated with ultraviolet light.
- Some dairy products and juices are artificially fortified (and so on their labels).
Most people meet their vitamin D needs partially or fully through sun exposure.
An exposure of 10 to 30 minutes (it takes more time in winter than in summer), in particular between 10 in the morning and 4 in the afternoon, daily or at least twice a week, with face, bare arms, hands and legs , without sunscreen or protective creams leads to a sufficient synthesis of vitamin D.
But older people and those with dark skin are less able to produce vitamin D through sun exposure. It is important to note that UVB radiation does not pass through the glass, so sun exposure through a closed window is of no use at all.
But vitamin D doesn’t work alone . He is part of a large orchestra. For the orchestra to function well, an excellent soloist is not enough; all instruments must be well tuned. They are the rest of the micronutrients that contribute to resistance against infections (zinc, calcium, vitamin C and many other antioxidants and anti-inflammatories).
In both the University of Navarra Follow-up study and PREDIMED, adequate monitoring of the Mediterranean diet ensured an adequate supply of all micronutrients. The eating pattern is a determinant of COVID-19 and it is surprising that, at this point, no one is talking about it.
Miguel A. Martínez González, Professor of Public Health, University of Navarra and Nerea Martín Calvo, Contracted Professor Doctor. Preventive Medicine and Public Health., University of Navarra
This article was originally published on The Conversation. Read the original.
