Abstract

Background and aims

This study aimed to evaluate serum 25-hydroxyvitmain D and zinc levels in coronavirus disease 2019 (COVID-19) patients in comparison to healthy subjects.

Methods

This was a single-center case-control study performed from March 20, 2020, to January 20, 2021, in Tehran, Iran. All patients diagnosed with COVID-19 based on a positive nasopharyngeal swab polymerase chain reaction (PCR) test were included in the case group. Controls were selected from patients referred for routine checkups who had a negative COVID-19 PCR test. Age, sex, marital and educational status, comorbidities, and serum 25-hydroxyvitmain D and zinc levels of patients were recorded.

Results

Ninety patients in the case group and 95 subjects in the control group who were sex and age-matched were studied. 25-hydroxyvitmain D levels higher than 20 ng/ml were observed in 58 (64%) cases and 72 (76%) controls (P = 0.09). The median 25-hydroxyvitmain D level in the case group was significantly lower than controls (26 (interquartile range [IQR] = 24) ng/ml vs. 38 (IQR = 22) ng/ml, respectively, P < 0.01). The median zinc level in the case group was 56 (IQR = 23) mcg/dL, while it was 110 (IQR = 27) mcg/dL among the controls (P < 0.01). There was no significant difference in the level of 25-hydroxyvitmain D and zinc between cases with and without comorbidities (P > 0.05). Susceptibility to SARS-CoV-2 infection could be predicted by serum 25-hydroxyvitmain D levels below 25.2 ng/ml (81% sensitivity; 48% specificity) or zinc levels below 86.3 mcg/dL (93% sensitivity; 92% specificity).

Conclusions

Low serum zinc and 25-hydroxyvitmain D levels appear to be risk factors for COVID-19 affliction; thus, the treatment of individuals with such deficiencies is recommended.

Introduction

The world is currently experiencing the third leading pandemic of coronavirus (CoV) infections. The outbreak of the new CoV infection began in late 2019 in Wuhan, China. The agent responsible was named the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), causing coronavirus disease 2019 (COVID-19) [1]. One of the most important issues about COVID-19 is the response of the patient’s body to the virus, which can be influenced by various factors. During the COVID-19 pandemic, interest in dietary supplements to support immune function has increased. Micronutrients in the human body may also be involved [2,3,4,5,6,7,8,9,10].

25-hydroxyvitmain D is a fat-soluble steroid molecule that has hormonal-like effects [11, 12]. 25-hydroxyvitmain D deficiency is a major health problem worldwide [13]. Recent studies have shown a high frequency of 25-hydroxyvitmain D deficiency in the Iranian population [14, 15]. A potential link between 25-hydroxyvitmain D deficiency and systemic infection has been demonstrated [16, 17]. The immunomodulatory role of 25-hydroxyvitmain D affects the immune system. By inducing the secretion of antiviral peptides, 25-hydroxyvitmain D increases innate immunity and improves mucosal defenses [18,19,20]. The correlation of 25-hydroxyvitmain D levels with COVID-19 severity and mortality has been shown in retrospective studies on COVID-19 patients [21,22,23,24]. Also, 25-hydroxyvitmain D deficiency or insufficiency has been shown to be higher in patients hospitalized with COVID-19 [25]. Overall, poor 25-hydroxyvitmain D status appears to be associated with an increased risk of COVID-19 infection and severe disease; however, the causal relationship between 25-hydroxyvitmain D status and severe COVID-19 is not well-understood, as decreased 25-hydroxyvitmain D levels may be the consequent of severe disease instead of causing it [26].

Zinc is another important micronutrient, fulfilling various roles in the human body. High concentrations of zinc and the addition of compounds that stimulate zinc entry into the cell have been shown to inhibit the replication of various viruses that contain RNA, including influenza viruses [27]. Besides, the inhibitory effect of zinc on the net activity of rhinoviruses and the hepatitis C virus has been reported [28, 29]. Provided that zinc deficiency accounts for 16% of deep respiratory infections worldwide, there can be a link between zinc deficiency and the risk of COVID-19 infection or progression to severe forms of the disease [30].

Although there are different opinions about the consequences of 25-hydroxyvitmain D deficiency in COVID-19, what is certain is that Iranian society is facing severe 25-hydroxyvitmain D deficiency, especially in certain populations. The relationship between the various aspects of the disease, as well as infection or severity, needs to be investigated to provide information concerning the micronutrition supplementations necessary for overcoming the COVID-19 pandemic. Also, studies have shown that patients hospitalized with COVID-19 who had low serum levels of zinc had more severe manifestations than patients with normal zinc levels [31]. Hence, the current study aimed to evaluate serum levels of 25-hydroxyvitmain D and zinc in COVID-19 patients in comparison with controls.

Discussion

The present study compared healthy controls with COVID-19 cases in terms of serum 25-hydroxyvitmain D and zinc levels. Our results showed that median serum 25-hydroxyvitmain D and zinc levels in the case group were significantly lower than controls. However, there was no significant difference in the level of 25-hydroxyvitmain D and zinc between cases with and without comorbidities.

Various studies have been conducted to determine the association between COVID-19 and 25-hydroxyvitmain D. D’Avolio et al. compared COVID-19 PCR positive vs. negative cases and showed that plasma 25-hydroxyvitmain D levels were significantly lower in the PCR-positive patients [33]. However, their research was one of the initial studies conducted in this era, facing some limitations due to its timing and lacking some essential data about possible 25-hydroxyvitmain D supplementation. While our study results showed higher levels of 25-hydroxyvitmain D in PCR-negative cases, we only included patients who had no history of 25-hydroxyvitmain D supplementation. Nonetheless, sunshine-produced 25-hydroxyvitmain D and dietary 25-hydroxyvitmain D intake (expect supplementation medications) could have biased our results. Due to the customs of Iranian women’s way of clothing (Hijab), sunshine-produced 25-hydroxyvitmain D could be lower in female cases [34], though our sex-matched case-control study design restricts the confounding effect of this issue to some extent.

In line with our findings, a recent study by Hurst et al. showed higher frequency of 25-hydroxyvitmain D insufficiency/deficiency in hospitalized COVID-19 patients [25]. The potential roles of 25-hydroxyvitmain D in reducing the risk for COVID-19 include decreasing the replication and viability of SARS-CoV-2 through induction of antimicrobial peptides and binding to the host cell surface receptors, and decreasing the cytokine storm through promoting the body’s ability to reduce the production of inflammatory cytokines [35].

Meltzer et al.’s findings are also consistent with ours [36]. Their retrospective cohort study of 489 patients demonstrated that the relative risk of a positive COVID-19 PCR test in individuals who had insufficient 25-hydroxyvitmain D levels in the year before the COVID-19 pandemic was almost two-fold higher compared with individuals with sufficient 25-hydroxyvitmain D [36].

Moreover, it is well known that some nutrients, including 25-hydroxyvitmain D and zinc, play key roles in immune system integrity and function and are believed to have immunomodulatory effects. It has also been proposed that 25-hydroxyvitmain D and zinc, along with vitamin C, may have synergistic actions in the maintenance of tissue barriers. Based on the literature review, 25-hydroxyvitmain D and zinc deficiency can compromise the immune system, making individuals more susceptible to viral infections such as COVID-19, and increasing the likelihood of a poor disease prognosis [37]. However, it is not yet clear whether 25-hydroxyvitmain D deficiency leads to severe COVID-19 disease or 25-hydroxyvitmain D is reduced as a result of severe disease, potentially due to its consumption [26]. On the other hand, Maghbooli et al. demonstrated that oral 25-hydroxyvitmain D could improve immune function in COVID-19 patients with 25-hydroxyvitmain D levels below 30 ng/ml, reflected by increased blood lymphocyte percentage [38].

As reviewed by Biesalski, there is clear evidence that in different comorbidities like hypertension and diabetes, reduced plasma levels of 25-hydroxyvitmain D are seen [39]. In our study, there was no correlation between comorbidities and serum 25-hydroxyvitmain D level of COVID-19 patients, as was the case in the study of Giannini et al. [40]. Also, Pinzon et al. showed that there is no difference in 25-hydroxyvitmain D deficiency status between patients with and without comorbidities [41].

Few previous studies have investigated the association of serum zinc levels with SARS-CoV-2 infection. Most studies have compared zinc levels between COVID-19 patients with poor outcomes and those with mild disease [42]. On the other hand, Jothimani et al. showed that COVID-19 patients have lower levels of zinc than healthy controls, and comorbidities had no significant effects on the zinc levels in their study groups [31]. Also, Abdolahi et al. demonstrated significantly lower serum zinc levels in COVID-19 patients compared with healthy subjects [43]. On the other hand, Carlucci et al. showed that zinc may play a role in the therapeutic management of COVID-19. They reported that hospitalized COVID-19 patients who took zinc sulfate were more frequently discharged from the hospital and had lower mortality [44]. Nevertheless, Thomas et al. demonstrated no significant reduction in the duration of symptoms in COVID-19 patients who received high-dose zinc [45]. Overall, as an important signaling molecule, zinc can alter host defense systems. Also, by regulating leukocyte immune responses and modulating the nuclear enhancer of activated B cells and consequently altering cytokine production, zinc has a positive role in inflammatory conditions [46].

Although lower levels of 25-hydroxyvitmain D may make individuals prone to COVID-19 affliction, the opposite may not be true. Respiratory diseases can reduce 25-hydroxyvitmain D levels. Based on the role of 25-hydroxyvitmain D and its receptor in immunomodulatory events, 25-hydroxyvitmain D is thought to be consumed in respiratory infections; however, whether a similar trend in 25-hydroxyvitmain D reduction applies to COVID-19 infection is not known [26]. On the other hand, Souza et al. hypothesized that organisms like SARS-COV-2 could consume zinc for their own functions or for the modification of their receptors, which may decrease the serum levels of zinc [37]. On the other hand, some studies have shown the anti-SARS-CoV-1 effects of zinc [47].

Our study had some limitations. First, the severity of COVID-19 was not evaluated. However, we were exploring the link between 25-hydroxyvitmain D and zinc levels with susceptibility to SARS-CoV-2 infection, and disease severity was not our main objective. Moreover, we did not assess the duration of daily sunshine exposure and the dietary intake of 25-hydroxyvitmain D and zinc; these could have influenced the results. Furthermore, we did not take body mass index (BMI) into account as BMI can be a confounding factor of 25-hydroxyvitmain D and zinc status [48, 49]. Also, the 25-hydroxyvitmain D status of the participants prior to admission is not known and we did not measure 25-hydroxyvitmain D binding protein.

Conclusion

Our study showed extremely lower levels of 25-hydroxyvitmain D and zinc in COVID-19 patients, independent of age, sex, and comorbidities. 25-hydroxyvitmain D and zinc deficiency may be important factors in determining susceptibility to COVID–19. Therefore, we recommend the diagnosis and treatment of individuals with low serum 25-hydroxyvitmain D and zinc levels.