LaNutrition.fr: Does fluctuating levels of vitamin D in the blood at least partially explain our susceptibility to upper respiratory tract infections in winter?
Dr. William Grant: Yes. But there are other factors as well. For example, long-wave ultraviolet radiation, or UVA, which makes up more than 95% of the sun’s ultraviolet radiation, releases nitric oxide from the subcutaneous nitrogen compounds, nitrates. Nitric oxide lowers blood pressure and kills viruses. In addition, in summer, UVA rays can destroy viruses in minutes.
LN: Most of the evidence supporting an association between vitamin D status and a favorable prognosis after infection with COVID-19 comes from observational studies with known limitations.
Dr. WG: Although these studies have problems, they may provide very good evidence for their role vitamin D reducing the risk of disease. One of the problems with these studies is that vitamin D levels measured at the time of diagnosis of COVID-19 may have decreased due to the disease. The solution is to rely on pre-disease vitamin D levels, but not too long before they are not similar to pre-disease vitamin D levels. The best observational study to date shows that higher vitamin D levels are associated with a modest reduction in the risk of COVID-19, but a significant reduction in mortality with high vitamin D levels at 125 nmol/L, which is close to optimal.
LN: However, there have been few clinical trials of vitamin D supplementation in infected patients, and many have not been placebo-controlled or adequately randomized.
Dr. WG: A good clinical trial was conducted in Turkey and several in Spain. One from Turkey gave half of the participants high doses of vitamin D3 over 3 to 14 days to increase vitamin D levels above 75 nmol/L. The only significant finding was a reduction in mortality. Better outcomes were obtained with calcifediol or 25-hydroxyvitamin D in Spain, including a reduction in intensive care visits. The advantage of calcifediol is that it increases vitamin D levels within hours, rather than the days of vitamin D3, which must first be metabolized in the liver.
LN: Should governments adopt national strategies to address vitamin D deficiency in the age of COVID-19?
Dr. WG: Well, it’s an interesting idea, but there are quite a few obstacles to it. First, health authorities and most doctors do not believe that vitamin D is very effective, especially since most randomized clinical trials have not found any beneficial effects of supplementation. A second obstacle is that implementing such a program would require each country to analyze the available data. By the time this job is done, it will be too late. A third obstacle is that high-dose supplementation is required first, which is not well understood. Many believe that high doses of vitamin D are toxic.
LN: What is the optimal 25(OH)D concentration range and how to achieve it in winter?
Dr. WG: The optimal range for vitamin D is 75-150 nmol/L or 30-60 ng/mL. To achieve this in the winter, one could use, say, 25,000 IU per day for maybe ten days, then 5,000-10,000 IU per day. However, it is not always easy to get high doses of vitamin D without a prescription in some parts of Europe.
LN: Should I take vitamin D supplements for flu and COVID-19 infections? How much and what form of vitamin D?
Dr. WG: It is best to increase vitamin D levels before infection or illness. There are multiple mechanisms by which vitamin D reduces the risk and severity of COVID-19, most notably by reducing viral viability and replication through the induction of cathelicidin and defensins. [NdE : qui font partie de l’immunité innée]and reduce the risk of cytokine storms that can damage organs. Even using high doses of calciferol after COVID-19 did not reduce length of hospital stay or symptoms, according to a study in Turkey. Calcifediol would be better, but harder to get. It seems the most important thing is to start taking it at the first symptoms. However, it is also a good idea to use other supplements such as vitamin C, magnesium and zincas well as certain medicines.
Also read: Vitamin D needs magnesium to function
LN: Do you take vitamin D only in the winter or year round? how much do you charge
Dr. WG: I take vitamin D3 from 5000 to 10000 IU/day. At 5000 IU/d, my vitamin D level is about 150 nmol/L. At 10,000 IU, that’s more than 200 nmol/L. I live in San Francisco, where it’s foggy and cloudy in the summer, and I work indoors, so the season doesn’t affect my doses at all; however, I have recently increased my intake to 10,000 IU/d due to the rapid spread of the Omicron variant.
To go further, read: Let’s stop sabotaging our immunity