Published on January 8th in La Revue du Practitionien, an open letter signed by 73 experts and six French scientific communities invites physicians to prescribe vitamin D to infected individuals and the general population.
The idea put forward is not new. This winter, the UK launched a campaign to distribute vitamin D supplements free of charge to 2 million elderly and vulnerable people in hopes of reducing the risk of developing severe Covid-19. In November, the government attributed its decision to the "potential benefits of vitamin D" from Covid-19. 20% of Britons, especially the elderly, overweight, and black people, are deficient in this vitamin. Is there a scientific basis for the positive effect of vitamin D in the fight against Covid-19?
Vitamin D produced by the skin after sun exposure (which is actually a hormone) is also found in oily fish, egg yolks, and some mushrooms. It is also present in fortified foods and as a medicine. Vitamin D is essential for bone growth and mineralization; severe deficiency can lead to rickets in children and osteomalacia in adults. It is involved in many physiological processes, playing a large role in the immune process.
In recent months, several scientific studies have reported a large number of patients with vitamin D deficiency among people hospitalized with COVID-19. A study published September 3 in the journal Jama showed that the risk of testing positive for Covid-19 is higher in people with vitamin D deficiency. Finally, a cross-sectional analysis of data from Europe showed that deaths from Covid-19 are significantly associated with the level of vitamin D in the population. At the same time, the countries with the lowest rates have a higher number of infections and deaths.
Cause or effect?
"In addition, blacks and ethnic minorities, who are more likely to be deficient in vitamin D due to darker skin tones, appear to be more infected with Covid-19 than whites," the Lancet wrote in May. All of these factors lead some scientists to think that vitamin D can protect against Covid-19, as well as against severe forms of the disease.
However, Professor Philippe Autier of the University of Strathclyde urges "to be wary of reverse causation." “Now we know that the concentration of vitamin D in the blood decreases sharply during the inflammatory process, whether it is acute (as with Covid-19) or chronic. But the question of whether these low levels are a cause or a consequence of the disease has not been clarified after three decades of active research," he explains. The scientist is inclined to the second hypothesis.
As evidence, he cites numerous clinical studies of the use of vitamin D in various fields as a treatment or preventive measure. They almost never led to positive conclusions. The only exception is a 2017 meta-analysis of 25 scientific studies that found that vitamin D intake reduced the risk of respiratory infections, especially in people with vitamin D deficiency.
In June, the UK's National Institutes of Health decided against recommending vitamin D for the prevention or treatment of COVID-19 due to insufficient evidence of its effectiveness. He confirmed his opinion in September. "As with any drug, only selective clinical trials (with a placebo group) can give a clear answer to the question of the effect of vitamin D on Covid-19. At this point, this is not the case," Professor Olivier Lamy, head of therapeutic departments at the University Hospital of Lausanne, summarizes.
Clinical trials should start at a hospital in Oslo. They will determine if cod liver oil (rich in vitamin D) may be protective. The study will be attended by 70 thousand people. "At best, vitamin D deficiency will be just one of the many factors that affect Covid-19. But there is good reason to believe that vitamin D, being inexpensive and well-tolerated, could have beneficial effects," says specialist Adrian Martino of London Queen Mary University.
Read the original text at Le Figaro