Vitamin D – known as the “sunshine vitamin because it’s produced in your skin in response to sunlight – has been shown to reduce the risk and to help treat numerous medical conditions. It helps regulate the amount of calcium and phosphate in the body that are necessary for keeping bones, teeth, and muscles healthy. A lack of vitamin D can lead to bone deformities such as rickets in children and bone pain caused by a condition called osteomalacia in adults. 

The fat-soluble vitamin (stored in body fat) has been shown in medical studies to reduce depression, promote weight loss and minimize the risk of developing heart disease and multiple sclerosis (and other autoimmune diseases), and even of getting the flu.  

Sitting in the sun for long periods, however, is dangerous because it raises the risk of skin cancer and ages the skin. So one should eat foods rich in vitamin D, such as salmon, sardines, herring and mackerel, egg yolks, fortified dairy products, and breakfast cereals with a minimum of or no sugar or take vitamin D drops or pills as recommended by one’s doctor. One would have to consume a lot of all these to have an overdose. 

Vitamin D deficiency (VDD) is a global health problem, and its high prevalence in the Middle East is well established. Epidemiological risk factors for VDD include more pigmentation in the skin low sun exposure, the wearing of skin-covering clothes and a diet low in fish and dairy products. Studies have previously shown that social habits in specific ethnic groups and a preference to wear long clothing outdoors are independent risk factors for VDD, particularly among women. 

Now, a new study conducted by the Azrieli Faculty of Medicine of Bar-Ilan University (BIU) in Ramat Gan (near Tel Aviv) and its affiliate Galilee Medical Center (GMC) is among the first to show that a pre-infection deficiency of vitamin D is linked with increased COVID-19 severity and higher risk of death. 

Previous studies focusing on the association between vitamin D levels and SARS-CoV-2 infection have produced mixed results. Most of those measured vitamin D levels when patients were already sick, which can complicate interpretation of the results. The new Israeli study assessed this correlation using low levels of vitamin D measured before infection and focused on disease severity. 

The records of individuals with positive PCR tests for COVID-19, who were admitted between April 2020 and February 2021 to GMC in the northern Israeli city of Nahariya were searched for vitamin D levels measured 14 to 730 days before the positive test.

Of 1,176 patients admitted, 253 had vitamin D levels recorded prior to COVID-19 infection. Compared with mildly or moderately diseased patients, those with severe or critical COVID-19 disease were more likely to have severe pre-infection vitamin D deficiency with levels less than 20 nanograms per milliliter.  

The study was recently published on MedRxiv (not yet peer reviewed) and is currently being submitted to a peer-reviewed journal.

“This study can highlight the risks of vitamin D deficiency in terms of COVID-19,” stressed Dr. Amiel Dror of GMC and the Azrieli Faculty of Medicine who led the study. “Vitamin D is often associated with bone health. We’ve shown that it may also play an important role in other disease processes such as infection.”

Prof. Michael Edelstein, also of the Azrieli Faculty, added: “It is still unclear why certain individuals suffer severe consequences of COVID-19 infection while others don’t. Our finding adds a new dimension to solving this lingering puzzle. In Israel, where vitamin D deficiency is common in certain population groups, this finding is particularly important.”

The authors noted that the link between low vitamin D levels preceding infection and severe COVID-19 does not necessarily imply that giving vitamin D to COVID-19 patients will decrease the risk of severe disease. However, it does underscore the need to understand how to mitigate the effect of vitamin D deficiency.