Vitamin D could be a piece of COVID-19's 'complex puzzle,' Israeli scientists say, after a new study finds a link between deficiency and severe illness

• Low levels of vitamin D prior to catching COVID-19 were linked to worse illness, a study found.
• Vitamin D helps bolster the immune system to tackle viruses that attack the lungs, researchers said.

Israeli scientists said they found "striking" differences in the chances of getting seriously ill from COVID-19 when they compared patients who had sufficient vitamin D levels prior to contracting the disease with those who didn't.

A study published on Thursday in the research journal PLOS One found that about half of people who were vitamin D deficient before getting COVID-19 developed severe illness, compared to less than 10% of people who had sufficient levels of the vitamin in their blood.

We know vitamin D is vital for bone health, but its role in protecting against severe COVID-19 is less well established.

The latest research was the first to examine vitamin D levels in people prior to them contracting COVID-19, the study authors said.

Dr. Amiel Dror, a study author and physician at the Galilee Medical Center, said of the findings, "We found it remarkable, and striking, to see the difference in the chances of becoming a severe patient when you are lacking in vitamin D compared to when you're not," The Times of Israel reported.

The findings come from 253 people admitted to Galilee Medical Center in Nahariya, Israel, between April 7, 2020, and February 4, 2021 — a period before the highly infectious Omicron variant emerged.

Dror said the findings suggested that vitamin D helped bolster the immune system to deal with viruses that attack the respiratory system.

"This is equally relevant for Omicron as it was for previous variants," Dror said.

The research doesn't prove that vitamin D protects against COVID-19 and isn't a green light to avoid vaccines and take vitamins instead. Vaccines cut the risk of Omicron hospitalization, particularly after a booster, by up to 90%, the UK Health Security Agency said.

Most vitamin D comes from direct sunlight on the skin. It's also found in foods such as fatty fish, mushrooms, and egg yolks and in supplements.

Vitamin D levels of more than 20 nanograms per milliliter are considered sufficient for most people, said the Centers for Disease Control and Prevention — which is the benchmark used by the researchers from Bar-Ilan University and Galilee Medical Center.

Research compiled before the emergence of COVID-19 and published in The Lancet found that vitamin D cut the risk of other respiratory infections, compared with dummy drugs.

But for COVID-19, early findings have been inconsistent: Some studies have found a link between low vitamin D levels and severe COVID-19, while others have concluded that the vitamin wasn't protective.

It wasn't clear — even from those studies with results showing a positive correlation between low vitamin D levels and severe COVID-19 — if depleted vitamin D came before or after people became sick, the Israeli researchers said.

Despite the new data from Israel, we still don't know if low vitamin D levels cause people with COVID-19 to develop serious disease.

Underlying conditions that reduce vitamin D can also make people more vulnerable to severe COVID-19, for example.

The Israeli researchers cautioned that vitamin D was "one piece of the complex puzzle" underlying severe COVID-19, in addition to comorbidities, genetic predisposition, dietary habits, and geographic factors.

"Our study warrants further studies investigating if and when vitamin D supplementation among vitamin D deficient individuals in the community impacts the outcome of an eventual COVID-19 episode," they said.