The covid 19 virus is responsible for an infection with very different evolution depending on the individual. It can be almost inapparent (asymptomatic or paucisymptomatic), or on the contrary manifest itself by serious damage, in particular to the respiratory system, which can lead to death. Research on the factors responsible for these differences has been very active, as they can lead to targeted protective strategies or measures. Thus, the association of advanced age or certain comorbidities with a high incidence of serious forms has made it possible to orient and prioritize the implementation of certain measures, including vaccination.
Very early on, observations indicated that a vitamin D deficiency might be one of the circumstances associated with an increased risk of covid 19 and severe form (1). These observations were guided by previous work that showed a protective effect of vitamin D once morest acute respiratory distress syndrome (ARDS) which can be a complication, often fatal, of certain respiratory infections (2). A possible protection once morest the flu, the particular severity of covid 19 in the elderly or obese (two conditions often associated with hypovitaminosis) and the winter preponderance of infections (the lack of exposure to the sun favoring the deficit) had also oriented towards a possible role of vitamin D in the pathophysiology of the disease.
Vitamin D is known for its role in calcium metabolism (intestinal absorption, bone fixation). But it has other effects, antiviral and anti-inflammatory, mediated by its action on the angiotensin-converting enzyme type 2 (ACE2) and the regulation it exerts on the production of cytokines by macrophages and the lymphocytes.
Several works, including those of C. Annweiler in France, have drawn attention to the link between vitamin D level and the evolution of covid 19, indicating a potential beneficial effect of the vitamin on the prognosis of infection in people elderly.
These data led, from 2020, the Academy of Medicine to recommend vitamin D supplementation (800 to 1000 units per day) for the prevention of severe forms of covid 19 in people under 60 years of age from the diagnosis of infection carried out (3). For people over 60, she recommended measuring serum 25(OH)D immediately in case of infection and giving a loading dose of 50,000 to 100,000 units of the vitamin in case of deficiency. In its opinion, the Academy specified that vitamin D should not be considered as a preventive or curative treatment of the infection, but as an adjuvant to these treatments.
In January 2021, many doctors and researchers suggested that supplementation be provided throughout the year to people at risk of hypovitaminosis (people aged 80 and over, people living in nursing homes, dependent, frail or obese) , and in winter to the entire population (4). The 25(OH)D assay, which is not a routine examination, would only be necessary for people with impaired calcium metabolism.
The just-published Israeli study looked at 25(OH)D concentrations measured in 253 people in the period (14 to 730 days) before SARS-CoV-2 infection (5) . A mathematical model integrating seasonal variations was used to assess the concentration at the time of infection. The authors highlight a correlation between vitamin deficiency and severity of the infection: the incidence of severe forms was 14 times higher in people with a 25(OH)D concentration below 20 ng/mL than in those exceeding 40 ng/mL. The study shows that vitamin deficiency may well be a predisposing factor for serious infection, not a consequence of it, as initial findings (vitamin dosage in people who were already ill) did recall. The authors declare that they have demonstrated, in the case of covid 19, the ability of vitamin D to strengthen the defenses once morest viruses affecting the respiratory system, an ability that is undoubtedly valid for all variants of SARS-CoV- 2. They specify that vitamin D intake cannot replace vaccination but in turn recommend that supplementation be implemented in the general population throughout the duration of the epidemic.
In France, a survey carried out in the 2010s showed that, while vitamin D deficiencies (serum concentration of 25-hydroxyvitamin D, or 25(OH)D, below 10 ng/mL) are rare and concern vulnerable populations , insufficiency (concentration between 20 and 30 ng/mL) and deficiency (concentration between 10 and 20 ng/mL) were very common (6). In 2012, the Academy of Medicine recommended “that greater attention be paid to the vitamin D status of the population in France” and recommended a reassessment of vitamin D intake in the French population, leading to possible supplementation by orally (7).
References
- Grant WB, Lahore H, McDonnell SL, Baggerly CA, French CB, Aliano JL, Bhattoa HP. Evidence that Vitamin D Supplementation Could Reduce Risk of Influenza and COVID-19 Infections and Deaths. Nutrients. 2020 Apr 2;12(4):988. doi: 10.3390/nu12040988. PMID: 32252338; PMCID: PMC7231123.
- J. Xu, J. Yang et coll. Vitamin D alleviates lipopolysaccharide induced acute lung injury via regulation of the renin angiotensin system. Molecular medicine reports vol. 16,5 (2017): 7432-7438.
- Vitamin D and Covid-19, Press release from the National Academy of Medicine, May 22, 2020
- Beneficial effect of vitamin D in Covid: what is the data? The Practitioner’s Review, January 7, 2021
- A.A. Dror, N. Morozov et coll. Pre-infection 25-hydroxyvitamin D3 levels and association with severity of COVID-19 illness. PLoS ONE 17(2): e0263069
- M. Vernay, M. Sponga et al. Vitamin D status of the adult population in France: the National Health Nutrition Study (ENNS, 2006-2007). Bull Epidemiol Hebd 2012;16-7:189-94
- Report of the National Academy of Medicine. Vitamin status, extra-osseous role and daily vitamin D requirements. Bull Acad Natle Med. 2012, 196, 1011.
