Vitamin D deficiency in the setting of COVID-19 can lead to over-expression of renin (an enzyme produced in the kidneys) and subsequent activation of the renin-angiotensin-system, a critical regulator of blood pressure, inflammation, and body fluid homeostasis. Disturbances in this system can drive poor outcomes, such as acute respiratory distress syndrome (ARDS) and death in COVID-19. Findings from a recent study suggest that supplementation with calcifediol, an intermediate molecule in the production of the active form of vitamin D, reduces the risk of death due to COVID-19.

Unlike other vitamins – trace nutrients that must be consumed in the diet – vitamin D is a steroid hormone that is produced in the body. Its synthesis occurs in a stepwise manner that begins in the skin following exposure to ultraviolet light and ends in the kidneys with the production of 1α,25-dihydroxyvitamin D, or 1,25(OH)2D, the active steroid hormone.

The retrospective cohort study involved 537 patients living in Spain who were hospitalized with COVID-19 during a three-month period in early 2020. Of these patients, 79 received vitamin D treatment providing 532 micrograms (~21,000 IU) of calcifediol on the first day of their hospital stay, and 266 micrograms of calcifediol (~9,300 IU) on days 3, 7, 14, 21, and 28. The primary outcome measure was death during the first 30 days of hospitalization.

During the study period, 20 percent of patients who did not receive vitamin D treatment died. More of the patients in the untreated group had chronic kidney disease, but fewer had diabetes, cancer, high blood pressure, or other cardiovascular diseases, compared to the treated group. They also had low oxygen saturation levels and were more likely to have elevated inflammatory markers. Twenty-five percent of this group developed ARDS. Only 5 percent of those who received vitamin D treatment died, and only 10 percent of these developed ARDS, even though the patients in this group were more likely to have comorbidities (coexisting health conditions) compared to the untreated group.

These findings suggest that vitamin D reduces the risk of severe outcomes, including death, in patients with COVID-19. The authors of the study noted that this small study was observational in design, possibly limiting the interpretation of these findings. They also noted that although none of the patients in this cohort were assessed for vitamin D deficiency, most of the people who live in southern Spain tend to be deficient during the time of year when the study was conducted.

• Link to full study.