Comment to article: Mortality due to COVID-19 in Spain and its association with environmental factors and determinants of health / Mortalidad por COVID-19 en España y su asociación con factores ambientales y determinantes de la salud.

Autores: Dante R. Culqui Lévano, Julio Díaz, Alejandro Blanco, José A. Lopez, Miguel A. Navas, Gerardo Sánchez‑Martínez, M. Yolanda Luna, Beatriz Hervella, Fernando Belda and Cristina Linares


What is known about this subject?

Mortality due to COVID-19 has been rather high. During the peak of the pandemic (first wave), an excess mortality of about 50% was observed, as compared to data from previous years. While there have been many pandemics over the years with high mortality rates, one of the peculiarities that differences this pandemic is that the reasons for the potential high transmission and high mortality rates of COVID-19 have not been clearly identified.

From the beginning of the pandemic, various researchers have tried to find answers to what factors could be linked to higher COVID-19 mortality. To address the latter, research studies have examined environmental factors such as the increase of ozone, or the increase of carbon dioxide (CO2), nitrogen dioxide (NO2), PM10, and PM2.5 (particulate matter by size), amongst other air pollutants. However, no strong link between the various factors studied and mortality due to COVID-19 in Spain had been found.

Over the last few years, a large number of studies have identified the adverse effects of environmental pollution on human health. In this regard, it has been suggested that the widely studied long-term exposure to certain air pollutants could be responsible for at least 16% of global deaths. However, human being is not only exposed to long-lasting air pollution but also to short-term exposure to certain pollutants which could equally affect their health, and which are increasingly being linked to more health conditions.

The truth is that in spite of the fact it may be difficult to identify a precise mechanism in which pollutants act on certain pathologies, we should be aware that human beings are permanently surrounded by air pollutants that can affect their health (see figure 1). On the other hand, these pollutants do not act in isolation, and may or may not affect the health of those exposed depending on the socio-economic conditions of each person.


What does this study add to the existing literature?

Since the beginning of the pandemic, efforts have been made to prove the relationship between mortality due to COVID-19 and air pollution. In this regard, many ecological studies have been published, and yet only a few with reliable methodology identify a link between pollution and mortality due to COVID-19.

An important contribution of this study is the fact that, from a methodological point of view, identifying the relationship between pollution and mortality due to COVID-19 using a generalized linear model (analysis methodology) allows, on the one hand, to include multiple pollutants simultaneously, such as PM10, NO2, and on the other hand, to incorporate to the same model meteorological variables such as temperature and humidity, something which until the time of publication of this article was hardly seen on other research conducted. Consequently, we consider this article to be innovative, both for the findings and the methodology used which allowed to build a model that incorporated meteorological variables such as temperature and humidity with air pollutants such as NO2 and PM10, and, in addition, to analyse the relationship with some socio-economic variables (intervening variables), with the aim of studying other variables that could influence the health-illness process to a greater or lesser extent. We believe the latter has improved the quality of the analysis.

Furthermore, this study used data from 41 out of the 52 provinces in Spain. This allows for a better approximation to the reality in Spain.


What are the implications of the findings?

This study was useful in demonstrating the role of air pollutants such as PM10, which is associated with increased mortality due to COVID-19 in 66% of the Spanish provinces studied. It was also useful in identifying that the role of temperature was much smaller when analysed together with air pollutants.

These findings differ from other studies that examined meteorological variables, such as temperature and humidity, concluding that temperature played an important role in the increase of mortality due to COVID-19. By including both air pollutants and meteorological variables in the same model, our study demonstrated that PM10 could influence the increase of mortality due to COVID-19 largely than temperature. On the other hand, when studying NO2 (mainly resulting from vehicle combustion emissions), an association with mortality due to COVID-19 was observed in a large number of provinces.

It is important not to disregard the real role that air pollutants have played in the increase of mortality due to COVID-19, and the role they will play in cities with high values of pollution, especially in large cities.


Dr. Dante R. Culqui Lévano PhD, MPH, MD.
Epidemiologist Medical Doctor (Technical team)
Sub-Directorate General for Environmental and Occupational Health
Directorate General for Public Health
Ministry of Health. Spain