Obesity, vitamin D deficiency and SARS-CoV-2 infection: A systematic review of the Spanish evidence and contribution of an original observational study in 389 patients

Abstract

Background. Obesity and vitamin D deficiency are two highly prevalent conditions independently linked to a worse clinical course of SARS-CoV-2 infection. However, Spanish evidence jointly analysing both factors together with infection risk remains scarce. Objectives. To synthesise the Spanish evidence on obesity, vitamin D deficiency and COVID-19 through a qualitative systematic review, and to provide original evidence through an observational study in 389 patients. Methods. A systematic review following the PRISMA 2020 guideline was conducted in PubMed, Embase and Scopus (2019-2025), finally including 19 Spanish studies (18 observational studies and 1 systematic review). In addition, an observational, analytical, cross-sectional study was carried out in 389 primary care patients (Valenciennes, France, exposure data referring to 2020), using multivariate logistic regression to analyse the association between obesity, vitamin D deficiency, supplementation and their interactions with COVID-19 infection and, exploratorily, with severity outcomes. Results. The systematic review showed a consistent association between obesity and greater COVID-19 severity (overall risk of bias moderate; GRADE certainty ranging from moderate to low-moderate depending on the outcome). In the original study, obesity was not associated with infection (adjusted OR 0.79; 95%CI 0.42-1.46), whereas vitamin D deficiency was independently associated with infection (adjusted OR 1.80; 95%CI 1.03-3.14; p = 0.039), with no significant interaction between both factors. Conclusions. Obesity is mainly associated with COVID-19 severity rather than infection risk, while vitamin D deficiency emerges as an independent risk factor for infection, reinforcing the clinical usefulness of its screening, particularly in patients aged 65 years or older and in women.