Abstract

La nouvelle infection au COVID-19 est une maladie respiratoire infectieuse sévère dont l'agent causal a été identifié comme un nouveau virus de la famille des coronavirus, SARS-CoV-2. Comme les autres coronavirus, des études montrent un neurotropisme du COVID-19, induisant des lésions démyélinisantes comme dans le syndrome de Guillain-Barré.

Plus particulièrement, une note italienne conclue qu'il y a un déficit significatif en vitamine D chez les patients infectés par le COVID-19.

Dans cette étude, nous avons utilisé un test de corrélation de Pearson sur des données de santé publique et météorologiques, dans le but de statuer sur une possible relation entre l'ensoleillement et la mortalité induite par le COVID-19. Pa exemple dans la France métropolitaine continentale, la moyenne des heures d'ensoleillement est significativement (pour une p-value de 1.532 × 10⁻³²) corrélée au taux de mortalité due au COVID-19, avec un coefficient de Pearson de −0.636.

Cette corrélation établit un effet protecteur de l'ensoleillement contre la mortalité due au COVID-19. Ce manuscrit est proposé uniquement pour une discussion académique et les hypothèses et ses conclusions doivent être confirmées par d'autres recherches.

Mots-clés: COVID-19; Coronavirus; France; Corrélation; Vitamine D; Photothérapie; UV.

1. Introduction

The novel coronavirus pneumonia (COVID-19) is a contagious acute respiratory infectious disease whose causative agent has been demonstrated to be a new virus of the coronavirus family, SARS-CoV-2. This illness was first evinced in December 2019 in the Seafood Market of Wuhan, Hubei Province, in southern China (^{Wang et al., 2020; Huang et al., 2020}). Patients with the coronavirus pneumonia typically exhibit a fever, with temperature above 38° © and other symptoms such as dry cough, fatigue, dyspnea, difficulty breathing, and diarrhea (^{Chang et al., 2020; Guan et al., 2020; Wang et al., 2020; Diao et al., 2020}). Furthermore, this diseases has a relatively high transmission rate as compared to other upper respiratory illnesses. As a result of this and other factors such as international travel and trade, the initial epidemic has turned into a pandemic in March 2020, with hundreds thousands of individuals confirmed to be infected worldwide – and most likely millions of unreported cases (^{Diao et al., 2020}).

Similar to other coronaviruses-caused illnesses (^{Talbot and Jouvenne, 1992}), COVID-19 infection has shown some amount of neurotropism (^{Poyiadji et al., 2020; Zhao et al., 2020; Mao et al., 2020}), with lesions not unlike those of the Guillain-Barré demyelination (^{Zhao et al., 2020}) or hemorrhagic necrotizing encephalopathy (^{Poyiadji et al., 2020; Mao et al., 2020}). Meanwhile, it has long been noted that in the case of Guillain-Barré syndrome, vitamin D deficiency, in relation with high latitude climates, is both a causal and a risk factor (^{Tsujino et al., 2019; Elf et al., 2014}). Furthermore, a recent Italian note has demonstrated a significant vitamin D deficiency in a cohort of COVID-19 infected elderly women (^{Isaia and Medico, 2020}).

Therefore, it is important to assess the effect of vitamin D blood levels on COVID-19 infection rate and disease course, as it may offer preventative and/or curative options in the context of the ongoing pandemic.

Specifically in the context of continental metropolitan France, the correlation between sunlight exposure and SARS-CoV-2 infection will be studied in this article, by using an adjusted Pearson test applied to public health and weather data (^{Santé Publique France 2020; Météo France 2020; INSEE. Insee 2020}).

2. Methods

3. Results

4. Discussion

We have shown via Pearson correlation that sunlight exposure is significantly correlated (p-value: 1.532×10⁻³²) COVID-19 mortality rate in continental metropolitan France (Table 3), which is the main outcome of this study.

Besides, we acknowledge an interesting secondary finding: namely, the protective effect of life expectancy (Pearson r: 0.512; p-value: 7.951×10⁻³¹) and discuss it further as it appears counterintuitive, as older age is already been broadly documented as being associated with worse COVID-19 outcomes. However, we also note that in our sample life expectancy is strongly positively correlated with sunlight exposure (Pearson r: 1.628×10⁻³; p-value: 3.88×10⁻³¹), which indicates that life expectancy is a mere surrogate of sunlight exposure in this data set, and can therefore be safely explained out of this analysis.

This study is of course limited by two important factors: (1) lack of measurement time; (2) lack of direct vitamin D measurements; (3) confounding variables. First, the brief duration (2 months) across which measurements were taken did not allow us to well understand the time-evolution of the evinced correlations, a crucial point indeed in the context of a pandemic. Secondly, our data set did not include a variable measuring actual plasma vitamin D levels in the studied population, for which we used sunlight exposure as an imperfect surrogate. Last but not least, we are also concerned by the influence of other co-factors well-known to be associated with poor prognosis in Intensive Care Unit population infected by COVID-19, such as high BMI or diabetes (Table 3), and possibly other unknown population confounding variables.

Nevertheless, our regression, linked with the hypothesized physiopathological mechanism (^{Isaia and Medico, 2020}), suggests a first order effect at least. We thus contend that the findings presented in our analysis should be taken into account, in order to envision possibly effective yet inexpensive diagnostic and therapeutic options against the novel COVID-19.

Our conclusions could easily be tested and further assessed by screening the prevalence of COVID-19 infected among vitamin D deficient patients. In addition, in vitro cell studies and animal models could be of interest to test our statistical correlation and the physiopathological hypothesis.

Declaration of Competing Interest

None

Acknowledgement

References