Association of 25-Hydroxyvitamin D Level with COVID-19-Related in-Hospital Mortality: A Retrospective Cohort Study

Vitamin D and COVID-19-Revisited

Vitamin D, when activated to 1,25-dihydroxyvitamin D, is a steroid hormone that induces responses in several hundred genes, including many involved in immune responses to infection. Without supplementation, people living in temperate zones commonly become deficient in the precursor form of vitamin D, 25-hydroxyvitamin D, during winter, as do people who receive less sunlight exposure or those with darker skin pigmentation. Studies performed pre-COVID-19 have shown significant but modest reduction in upper respiratory infections in people receiving regular daily vitamin D supplementation. Vitamin D deficiency, like the risk of severe COVID-19, is linked with darker skin colour and also with obesity. Greater risk from COVID-19 has been associated with reduced ultraviolet exposure. Various studies have examined serum 25-hydroxyvitamin D levels, either historical or current, in patients with COVID-19. The results of these studies have varied but the majority have shown an association between vitamin D deficiency and increased risk of COVID-19 illness or severity. Interventional studies of vitamin D supplementation have so far been inconclusive. Trial protocols commonly allow control groups to receive low-dose supplementation that may be adequate for many. The effects of vitamin D supplementation on disease severity in patients with existing COVID-19 are further complicated by the frequent use of large bolus dose vitamin D to achieve rapid effects, even though this approach has been shown to be ineffective in other settings. As the pandemic passes into its third year, a substantial role of vitamin D deficiency in determining the risk from COVID-19 remains possible but unproven.

Very Low Vitamin D Levels are a Strong Independent Predictor of Mortality in Hospitalized Patients with Severe COVID-19

Background

There is controversy regarding the association between hypovitaminosis D and COVID-19 outcomes.

Aim of the study

We assessed the association between 25-hydroxyvitamin D levels and COVID-19 outcomes in hospitalized subjects with severe SARS-CoV-2 infection.

Methods

Retrospective cohort study. Serum 25-hydroxyvitamin D levels of subjects with severe COVID-19 pneumonia were measured at hospital admission, between March 17^th, 2020, and March 1^st, 2021.

Results

Out of 2,908 patients, 571 (19.6%) had vitamin D deficiency (defined as a serum 25-hydroxyvitamin D level <12.5 ng/mL [<31.25 nmol/L]), and 1069 (36.7%) had levels between 12.5 ng/mL (31.25 nmol/L) and 20 ng/mL 850 nmol/L). Compared to subjects without vitamin D deficiency, those with 25-hydroxyvitamin D level <12.5 ng/mL had higher rates of in-hospital mortality at 30 d (28.0 vs. 17.3%; p <0.001), global mortality (31.9 vs. 20.8%; p <0.001), mechanical ventilation requirement (23.8 vs. 17.2%; p <0.001), and significantly longer hospital stay (median [interquartile range] of 9 [6–17 d] vs. 7 [5–12 d], p <0.001). In the unadjusted analysis, the risk of in-hospital death was greater for patients with vitamin D deficiency (HR 1.43; 95% CI, 1.20–1.70; p <0.001). After adjusting for confounders, the risk of in-hospital death within 30 d remained significantly greater in patients with vitamin D deficiency (HR 1.46; 95% CI, 1.21–1.76; p <0.001). The risk was reduced but remained significant with 25-hydroxyvitamin D levels between 12.5 ng/mL and 20 ng/mL (HR 1.31; 95% CI 1.10–1.55, p = 0.02). In comparison with other clinical biomarkers, vitamin D deficiency was an independent predictive marker of in-hospital mortality after adjusting for confounders.

Conclusion

Very low 25-hydroxyvitamin D levels measured at hospital admission were significantly associated with in-hospital mortality and are a useful prognostic biomarker in severe COVID-19 patients.

Vitamin D, Thyroid Hormones and Cardiovascular Risk: Exploring the Components of This Novel Disease Triangle

The role of thyroid hormones (THs) in the cardiovascular (CV) system, through several direct and indirect effects is recognized. Even very small modification in TH levels (as those observed in subclinical hypothyroidism or hyperthyroidism, and low triiodothyronine syndrome) may adversely affect the CV system, whereas thyroid hormones benefit the CV system and improve the prognosis. There is also evidence of vitamin D effects on cardiometabolic disease (e.g., through modulation of endothelial and smooth muscle cell activity, renin-angiotensin-aldosterone system, nitric oxide, oxidative stress, and inflammatory response), as well as an association between vitamin D [25(OH)D] deficiency and autoimmune thyroid diseases or cancer, and a relationship between vitamin D concentration and titers of antibodies and thyroid autoimmunity replacement. Interestingly, experimental data indicate a direct effect of vitamin D on Type 2 deiodinase expression causing subsequential peripheral conversion of T4 into T3. However, the functional links among THs, vitamin D and the cardiovascular system, and clinical effects of coexisting abnormalities in this new troublesome triad, have not yet been reviewed. The main aim of this review is to discuss pathophysiology of this relationship, proposing new mechanistic insights involving vitamin D in the modulation of cardiometabolic disease and thyroid profile.