Según un estudio de la Universidad de Navarra publicado en la revista “Clinical Nutrition” en el que han participado 9.677 personas se ha demostrado que la dieta mediterránea podría reducir el riesgo de contagio de la Covid-19 hasta en un 64%.
Los beneficios que una nutrición saludable en la que se incluye el consumo de aceite de oliva virgen extra permite al sistema inmunitario una mayor resistencia frente al coronavirus SARS-CoV-2 y, por lo tanto, la infección frente al Covid-19. Sin embargo, no exiten pruebas de que haya alimentos concretos que curen o atenúen los efectos de la enfermedad de la covid-19. Pero este estudio demuestra que unos buenos hábitos alimenticios contribuyen a mejorar el sistema inmune, mejorando así la salud y, por tanto, reduciendo el impacto de una posible infección.
Objetivos del proyecto
Con este estudio, el equipo de la Universidad de Navarra) pretende evaluar la asociación entre una mejor adherencia a la dieta mediterránea y la incidencia de COVID-19 entre los participantes de una conocida cohorte mediterránea, el proyecto SUN (“Seguimiento Universidad de Navarra”).
El investigador Rafael Pérez Araluce, graduado en Farmacia y Nutrición por la Universidad de Navarra, y la doctora Silvia Carlos, vicedecana de alumnos de la misma Facultad, también profesora en el Departamento de Medicina Preventiva y Salud Pública de la Facultad de Medicina, han sido los principales autores del trabajo, junto a investigadores del CIBEROBN, como el catedrático Miguel Ángel Martínez-González.
La doctora Carlos explica que, para realizar el estudio, se identificaron los participantes que tuviesen un diagnóstico médico de infección junto a resultados positivos en pruebas diagnósticas de Covid-19 desde febrero hasta diciembre de 2020.
“Se excluyó a los profesionales de la salud, dada la alta exposición a la infección que, por desgracia, habían tenido. Si los hubiéramos incluido, los resultados se habrían distorsionado y no se podrían obtener recomendaciones de salud pública para el total de la población”.
Revista Clinical Nutricion:
In December 2019, an outbreak of pneumonia of unknown origin in the city of Wuhan (China) led to the isolation of a new coronavirus, 2019-nCoV or SARS-CoV-2 []. A few months later, on March 2020, the coronavirus disease, COVID-19, was officially declared a pandemic by the World Health Organization. With data updated to March 2021, it has caused more than 125 million cases and 2.8 million deaths throughout 223 countries [].Although there are already more than 100,000 articles Indexed in PubMed about COVID-19, there is still no clear treatment protocol and many options are being tested and studied []. Today, the main focus of action is prevention. On the one hand, different countries have taken non-pharmacological measures to reduce the spread of the virus, such as the use of masks, border closures, quarantines, limitation of social gatherings, or even home confinement, with great socio-economic repercussions. On the other hand, the first vaccines are being currently applied in order to meet ambitious goals. However, to achieve herd immunity, at the current vaccination rate, it will still take quite a few months or years, depending on the region, since the vaccination rate is being very uneven among different parts of the world [].In this context, research on different risk factors, which may increase or reduce the probability of contracting the disease is essential. Some of the best described factors are obesity or diabetes [,], both of which may underlie an important role for nutrition. Other important risk factors include hypertension, cancer, asthma or cardiovascular disease [,].Just because of its widely demonstrated beneficial role on these risk factors [], it would be worth recommending a high-quality dietary pattern such as the Mediterranean diet. However, some authors already have pointed out that there is a strong rationale for expecting a protective effect of the Mediterranean diet on COVID-19 [10, 11, 12, 13, 14].Despite these expectations, to our knowledge, there are still no epidemiological studies that support this hypothesis. Demonstrating this relationship could contribute a new tool to help in the fight against the virus, for which no efforts are small.With this study we aimed to evaluate the association between a better adherence to the Mediterranean diet and the incidence of COVID-19 among participants of a well-known Mediterranean cohort, the SUN (“Seguimiento Universidad de Navarra”) project.
2. Materials & methods
2.1 Study sample
The SUN Project is a prospective and multipurpose cohort study designed to evaluate different aspects of the dietary pattern and lifestyles, relating them to health outcomes. By the end of 2020 it already had nearly 23,000 participants, who are evaluated every 2 years through self-administered questionnaires. It is a dynamic cohort, so, although the recruitment started in 1999, it is permanently open. Participants are university graduates from all over Spain. The methods and many specific details of the SUN cohort have already been described [].In addition to the biennial questionnaires, during February to December 2020, a specific questionnaire on COVID-19 was sent to all participants. In this questionnaire they were asked whether or not they had undergone a diagnostic test for COVID-19. If this was the case, they were asked for the date and the result of the test. It also inquired about a medical diagnosis of the disease.
2.2 Outcome measurement
For the incidence of COVID-19, all those who reported a positive result in a SARS-CoV-2 diagnostic test were counted. We used this criterion because it is more specific than the clinical diagnosis. We only took into account the additional cases with medical diagnosis but without confirmation by a specific diagnostic test (probable cases) for sensitivity analyses.
2.3 Dietary assessment
The adherence to the Mediterranean diet was assessed using the Mediterranean Diet Score (MDS) proposed by Trichopoulou which has been most widely used to assess adherence to the Mediterranean diet []. This MDS takes into account 9 components of the diet, 1 point corresponds to moderate ethanol intake (5–25 g/d for women and 10–50 g/d for men), and another point to the monounsaturated-to-saturated fatty acids ratio, the point is given to those with a monounsaturated/saturated ratio at or above the sex-specific median. The other 7 points correspond to the consumption of food groups: 1 point is given to those who have a consumption equal or higher than the sex-specific median consumption on each beneficial food groups (cereals, fruits and nuts, vegetables, legumes and fish), or below the sex-specific median for two food groups that are not typical of the Mediterranean diet (meat and dairy products). The final punctuation ranges from 0 to 9.Data for creating this Index were taken from a previously validated semi-quantitative Food Frequency Questionnaire (FFQ) []. It consists in 136 items with consumption grouped in nine categories from “never or almost never” to “≥ 6 times a day”. This questionnaire is assessed at baseline and at 10 years of follow-up. Ethanol and fatty acids values were calculated by using data from updated Food Composition Tables [].
2.4 Other covariates
At baseline, standardized questionnaires were used for gathering information on demographic characteristics (age, sex, years of university education, profession and marital status), lifestyle habits (smoking status and physical activity) and anthropometric and clinical data (weight, height and comorbidities).This information is updated with different follow-up questionnaires. The diagnosis of new diseases and weight are updated in each of these follow-up questionnaires. Other variables, however, are updated less frequently, such as marital status (questionnaire at 14-year follow-up) or height (questionnaire at 10 years). For each of them we used the most recent available information.
2.5 Statistical analysis
First, we proceeded to the description of the different variables with different statistical parameters. For categorical variables we calculated the percentage of participants included in each group and for numerical variables we calculated the mean and standard deviation or the median and the interquartile range if the distribution of the variable did not follow a normal distribution.Secondly, to evaluate the possible effect of the adherence to the Mediterranean diet on the incidence of COVID-19, logistic regression models with successive degrees of adjustment were used to calculate Odds Ratios (OR) for COVID-19, for the 2 upper categories of the MDS (4–6 and 7 to 9) using the lowest category (≤ 3) as reference. We also estimated the association using the MDS as a continuous variable and assessing the effect for every 2 points. These ORs are expressed with their 95% confidence intervals. This analysis was repeated adjusting for the potential confounding variables. We excluded from the analysis participants below the percentile 1 or above the percentile 99 of total energy intake. In addition, we adjusted all models for total energy intake (as a continuous independent variable).All analyses were carried out both excluding and including health professionals (HP): doctors, nurses and pharmacists. Analyses were also repeated after stratifying by different subgroups (sex, age, smoking status and body mass index).Finally, some sensitivity analyses were performed including probable cases (those with clinical diagnosis of COVID-19 and without a positive test), those who were tested during the second wave of the pandemic (after August 2020) or those with comorbidities.We calculated the p for trend by estimating group-specific medians and treating the resulting variable as continuous.STATA software (version 16) was used for data analysis.
By the end of 2020 the COVID-19 questionnaire of the SUN cohort had been answered by 9,677 participants. However, 74 of them did not coincide with a participant in the SUN Project database, so the final number of subjects initially included in this study was 9,603. After excluding participants with total energy intake beyond percentiles 1st and 99th the study sample included 9,413 participants. Given the immense strength of the COVID-19 pandemic burden in Spain during 2020 and that the most relevant exposures for health professionals are related to their work in clinical care and not so much to nutritional factors, our main analyses focused on those participants who were not health professionals. A priori, a stratified analysis, with a breakdown of the sample into health professionals and not health professionals was established. This decision was based on consideration of the highly relevant differences in exposures between both types of participants in our cohort.Baseline characteristics of the population included in the study are shown in Table 1. It is a middle-aged population (mean age = 52.6 years), with a higher proportion of women, mostly married. Near half of participants were health professionals (44.8%), a very similar proportion of the total population of the SUN cohort. Regarding lifestyles, half of the participants had never smoked. A description of the most important conditions and chronic diseases potentially related to the risk of COVID-19 is also shown in Table 1.