Abstract: Open Medicine 2021; 16: 591–609 Research Article Darya Saeed Abdulateef*, Heshu Sulaiman Rahman, Jamal Mahmood Salih, Sangar Mahmoud Osman, Trifa Abdalla Mahmood, Shirwan Hama Salih Omer, Rana Adnan Ahmed COVID-19 severity in relation to sociodemographics and vitamin D use https://doi.org/10.1515/med-2021-0273 received January 7, 2021; accepted March 16, 2021 Abstract: Most COVID-19 cases are treated as outpatients, while the majority of studies on COVID-19 focus on inpatients. Little is known about the self-reporting and selfrating of the disease’s symptoms, and the associations of prophylactic use of dietary supplements with COVID-19 severity have not been addressed. The aims of this study are to evaluate COVID-19 severity and to relate them to sociodemographic characteristics and prophylactic dietary supplements. An observational patient-based study conducted through an online questionnaire on recovered COVID-19 patients. The patients were assessed for several severity parameters, sociodemographic parameters, and prophylactic dietary supplement use. A total of 428 patients were evaluated. Age and presence of comorbidities had positive associations with the severity parameters. The severe infection group had the highest proportion of patients stressed about COVID-19 (P < 0.05). Cigarette, but not hookah, smoking was significantly associated with less severe symptoms. Vitamin D negatively predicted disease severity (P < 0.05). In conclusion, stress, age, and presence of comorbidities were the most important positive predictors of COVID-19 severity, while prophylactic vitamin D use and smoking were significant negative predictors. The use of protective measures and other prophylactic dietary supplements was not significantly associated with symptom severity.  * Corresponding author: Darya Saeed Abdulateef, Department of Physiology, College of Medicine, University of Sulaimani, New–Street-27, Zone 209, P. O. Box: 334, Kurdistan Region, Sulaymaniyah, Iraq, e-mail: darya.abdulateef@univsul.edu.iq, tel: +96-477-0158-0313 Heshu Sulaiman Rahman, Jamal Mahmood Salih, Sangar Mahmoud Osman, Trifa Abdalla Mahmood, Shirwan Hama Salih Omer, Rana Adnan Ahmed: Department of Physiology, College of Medicine, University of Sulaimani, Kurdistan Region, Sulaymaniyah, Iraq ORCID: Darya Saeed Abdulateef 0000-0001-6516-8611 Open Access. © 2021 Darya Saeed Abdulateef et al., published by De Gruyter. 4.0 International License. Keywords: COVID-19, symptoms severity, vitamin D, smoking, online survey