Several studies are now suggesting that low vitamin D levels are linked to increased risk of getting COVID-19. And if you get COVID-19, low vitamin D levels are linked to a higher risk of developing serious symptoms requiring admission to intensive care, and also not surviving. These studies are observational and don't prove that vitamin D levels are the cause, but a number of studies from countries worldwide and several lines of research are suggesting the same thing.
The best source of vitamin D is sunlight, but if taking supplements - then take vitamin D3. Researchers, doctors, and medical organizations vary in their recommended dosages, but many (such as Mayo Clinic) suggest 1000 to 2000 IU per day. The minimum daily requirement is 600 IU.
Some studies also suggest that having adequate magnesium is needed for vitamin D to be metabolized well. Good food sources of magnesium are nuts, seeds (especially pumpkin seeds), peanut butter, whole grains, beans, leafy vegetables, some fatty fish (halibut, salmon, mackerel), milk, yogurt, dark chocolate, legumes (beans), quinoa, tofu, and bananas. Daily magnesium requirements are 420 mg for men, 320 mg for women. Food is generally considered a better source than supplements.
However, some researchers point out that having a disease (e.g. diabetes) or chronic inflammation results in lowering of vitamin D levels (and not that low vitamin D levels causes disease). We need good double-blind studies (people randomly assigned to groups, and no one knows who is getting what) to understand if it really is vitamin D that's causing beneficial health effects.
Excerpts from Medscape: Low Vitamin D in COVID-19 Predicts ICU Admission, Poor Survival
Having low serum vitamin D levels was an independent risk factor for having symptomatic COVID-19 with respiratory distress requiring admission to intensive care — as opposed to having mild COVID-19 — and for not surviving, in a new study from Italy.
"Our data give strong observational support to previous suggestions that reduced vitamin D levels may favor the appearance of severe respiratory dysfunction and increase the mortality risk in patients affected with COVID-19," the researchers report.
Luigi Gennari, MD, PhD, Department of Medicine, Surgery, and Neurosciences, University of Siena, Italy, presented these findings during the virtual American Society of Bone and Mineral Research (ASBMR) 2020 annual meeting.
Gennari told Medscape Medical News that this analysis suggests determining vitamin D levels (25 hydroxyvitamin D) in people testing positive for SARS-Cov-2 infection might help predict their risk of severe disease.
However, further research is needed to explore whether vitamin D supplements could prevent the risk of respiratory failure in patients with SARS-Cov-2 infection, he stressed.
In the meantime, Gennari said: "I believe that, particularly in the winter season (when the solar ultraviolet-B (UVB) radiation exposure does not allow the skin to synthesize vitamin D in most countries), the use of vitamin D supplementation and correction of vitamin D deficiency might be of major relevance for the reduction of the clinical burden of the ongoing and future outbreaks of SARS-CoV-2 infection."
"I think this body of work suggests that people should be taking supplements if they cannot increase sun exposure on a sustained basis," Meltzer said. "The abstract supports multiple prior findings that suggest that higher vitamin D levels are associated with improved outcomes."
And JoAnn E. Manson, MD, DrPH, of Harvard Medical School and Brigham and Women's Hospital, who was not involved with the research but has spoken about the topic in a video report for Medscape, said: "We know from several studies that a low vitamin D level is associated with a higher risk of having COVID-19 and severe illness, but correlation does not prove causation."
"I think that improving vitamin D status is a promising way to reduce the risk of severe illness, but we need randomized controlled trials to prove cause and effect," she told Medscape Medical News.
Gennari said several lines of evidence suggest that vitamin D deficiency might be a risk factor for COVID-19 severity.
Countries with lower average levels of vitamin D or lower UVB radiation exposure have higher COVID-19 mortality, and "demographic groups known to be at higher risk of vitamin D deficiency (such as black individuals, the elderly, nursing home residents, and those with obesity and diabetes) are at high risk of COVID-19 hospitalization/mortality," he noted.
There is a high prevalence of vitamin D deficiency in Italy, where mortality rates from COVID-19 have been particularly high.
To examine the relationship between vitamin D levels and COVID-19 severity/mortality, the researchers studied three groups:
- 103 symptomatic patients with COVID-19 with respiratory insufficiency who were admitted to a Milan hospital from March 9 to April 30.
- 52 patients with mild COVID-19, recruited from patients and staff from a nearby nursing home who had a positive test for COVID-19.
- 206 healthy controls, matched 2:1 with symptomatic patients of the same age, weight, and gender, from 3174 patients who had vitamin D measured during a routine check-up from January to March 2020.
Patients in the hospitalized group had lower mean vitamin D levels (18.2 ng/mL) than those with mild COVID-19 (30.3 ng/mL) or those in the control group (25.4 ng/mL).
Among symptomatic patients, mean vitamin D levels were inversely associated with interleukin (IL)-6 and C-reactive protein, "both of which are a direct expression of the inflammatory status," Gennari noted.
Of the 54 patients admitted to ICU, 19 patients died from respiratory distress after a mean of 19 days, "consistent with the literature," and the other 35 patients were discharged after a mean of 21 days.
Patients with severe COVID-19 who were admitted to ICU, as opposed to a ward, were more likely to be male, have at least one comorbidity, have higher baseline IL-6 levels and neutrophil counts, and lower lymphocyte and platelet counts. They also had lower mean vitamin D levels (14.4 vs 22.4 ng/mL) and were more likely to have vitamin D deficiency (vitamin D < 20 ng/mL; 80% vs 45%).
Patients admitted to ICU who died had lower baseline vitamin D levels than those who survived (13.2 vs 19.3 ng/mL).