Abstract: Received: 15 September 2020 | Revised: 8 December 2020 | Accepted: 10 December 2020 DOI: 10.1002/jmv.26726 RESEARCH ARTICLE The association between the level of serum 25(OH) vitamin D, obesity, and underlying diseases with the risk of developing COVID‐19 infection: A case–control study of hospitalized patients in Tehran, Iran Alireza Abdollahi1 | Hasti Kamali Sarvestani2 Sara Ghaderkhani4 Vahid Mehrtash1 | Maedeh Mahmoudi‐Aliabadi5 1 Department of Pathology, Imam Hospital Complex, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran | Zahra Rafat3 | | Bita Jafarzadeh1 | Abstract Background and Objectives: The outbreak of COVID‐19 has created a global public 2 Department of Medical Mycology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran 3 health crisis. Little is known about the predisposing factors of this infection. The aim of this study was to explore an association between the serum vitamin D level, Department of Medical Microbiology, School of Medicine, Guilan University of Medical Sciences, Rasht, Iran obesity, and underlying health conditions, as well as the vulnerability to COVID‐19 4 Department of Infectious Diseases and Tropical Medicine, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran Methods: We conducted a case–control study of 201 patients with coronavirus 5 Department of Laboratory, Imam Khomeini Hospital Complex, Tehran University of Medical Sciences, Tehran, Iran Correspondence Alireza Abdollahi, Department of Pathology, Imam Hospital Complex, School of Medicine, Tehran University of Medical Sciences, Tehran 1419733141, Iran. Email: Alireza.a1345@yahoo.com in the Iranian population. infection and 201 controls. Cases and controls were matched for age and gender. The study was carried out for 2 months (February 2020–April 2020) at Imam Khomeini Hospital Complex, Tehran, Iran. Serum 25(OH) vitamin D was measured using the enzyme‐linked immunosorbent assay method. Information containing age, gender, clinical symptoms, body mass index, computed tomography scan findings, and underlying health conditions related to each participant were elicited from health records. Results: A significant negative correlation (p = .02) was observed between the serum vitamin D level and developing coronavirus infection. Also, the results showed that the COVID‐19 cases were more likely to be overweight than the controls (p = .023). Diabetes mellitus, hypertension, and respiratory infections were found in 20.89%, 9.65%, and 6.96% of cases, respectively. These underlying health conditions were not significantly different between cases and controls (p = .81). Conclusions: Vitamin D deficiency and obesity are two main predisposing factors associated with the vulnerability to coronavirus infection in the Iranian population. KEYWORDS abdominal obesity, body mass index, COVID‐19, Iran, vitamin D J Med Virol. 2021;93:2359–2364. wileyonlinelibrary.com/journal/jmv © 2020 Wiley Periodicals LLC | 2359 2360 1 | ABDOLLAHI | BACKGROUND 3 | The world is now experiencing a major epidemic of coronavirus ET AL. MA T ER I A L S A N D M ET H O D S 3.1 | Study design and participants (CoV) infection that began in Wuhan, Hubei province, China, in late 2019. Coronavirus disease 2019 (COVID‐19) is the name for This was a matched case–control study involving adult hospitalized this disease and the virus that causes it is known as the severe patients at..