If thanks to hygiene measures, vaccines and antibiotics, mortality linked to infections has steadily decreased in recent years, chronic non-communicable diseases have seen their incidence increase.
However, among the main defendants, is singled out junk food “ which generates overweight, obesity and associated pathologies. In addition, we now know that obesity and diabetes increase the risk of contracting a severe form of Covid-19. Clearly, eating better is a way of prevention of chronic non-communicable diseases, but also infectious pathologies. And it goes through the intestinal microbiota filter.
This community of microorganisms has a key role in our health. Over time, a true symbiosis has indeed developed between this community of microbes and our organism. So much so that if the balance is upset, this can result in various immune-mediated inflammatory diseases. Now we know that the answer innate immune, the first line of defense against infections, triggers adaptive immune response.
We also know that this first response is the cause of the inflammatory reaction whose excesses are so dreaded in the event of Covid-19. And if we react more or less well, it is due to various factors making our immune defense system less efficient: age, resistance to antibiotics (when there is superinfection by bacteria), or even a disease. chronic.
When the microbiota is disrupted
Several pathologies have been associated with disturbances in the microbiota. Namely, obesity, diabetes, asthma, cancers, but also immune-mediated inflammatory diseases affecting the digestive tract (Crohn’s disease causing abdominal pain, chronic diarrhea, fatigue, loss of appetite and weight loss), the joints (rheumatoid arthritis which causes fatigue and joint pain) or the central nervous system (sclerosis in plaques and pain, fatigue, sensory and motor disorders, etc.).
The processes involved combine inflammation, oxidative stress, but also food and environment. We know that antibiotics, fine particles and nitrogen dioxide, as well as food contaminants have an impact on our microbiota. Recent data also suggests that in our industrialized societies, the intestinal microbiota moved away from the ancestral model. And one can also imagine that the rapid modernization of medical practices (antibiotics, cesarean…) Gradually deteriorated it, thus contributing to the spread of various diseases. However, its structure and functions are mainly shaped by the diet.
In western countries, this one is characterized by:
- very significant deficits in fibers, in Omega 3, antioxidants and probiotics ;
- excess saturated fatty acids, refined products often contained in ultra-processed products ;
- the presence of contaminants including residues of pesticides and certain additives such as emulsifiers and sweeteners in ultra-processed products.
Based on this observation, we can assume that a regime respecting the 3V rule (true, vegetal and varied), with on the one hand more fiber and antioxidant intake, And on the other hand less contaminants, allow reduce the risk of occurrence chronic diseases due to better functioning of our immune system. Such a regime approaches a Mediterranean diet, which is known to be negatively associated with inflammatory markers.
Aging, inflammation and immunosenescence
For Covid-19, which is a major pandemic, it is now clear that the indicators of population aging in Europe are correlated with the local intensity of the epidemic. It can easily be explained. Aging, in fact, results in the development of low noise inflammation which weakens the organism and promotes the appearance of various diseases.
It also induces a phenomenon of immunosenescence, that is, a loss of effectiveness of the immune system, leading to an increased risk of infections and possible complications. But this goes hand in hand with changes in the gut microbiota.
These changes are partly linked to a less diversified diet. By intervening on the diet older people thanks to the 3V rule while encouraging them to maintain physical activity, so we could help them stay healthy. Especially since this would reduce the intake of antibiotics, thus preserving the intestinal microbiota which is involved in the response of the immune defense system.
In practice, the structure and functions of this community are modulated by infections. When the microbiota is rich and stable, it effectively plays its role barrier against pathogens. But if, for various reasons – such as taking antibiotics or an unbalanced diet – its balance is altered, then the microbiota no longer fulfills its role properly, hence increased vulnerability to environmental pathogens.
The impact of chronic diseases
As chronic diseases are themselves largely associated with such imbalances or poor adaptation of the intestinal microbiota (or dysbiosis), they are therefore a risk factor for complications following a viral infection. Moreover, we know that secondary bacterial infections often complicate viral infections. And it could be that this superinfection is explained by the alteration of the microbiota induced by the initial infectious disease: this is what has been shown in mice, where the microbiota disrupted by the influenza virus produces less short-chain fatty acids, which goes hand in hand with a less bactericidal action of cells of the innate defense system in the pulmonary alveoli, resulting in increased sensitivity to secondary bacterial infections. However, when it comes to chronic diseases, the figures of the Covid-19 epidemic are telling …
So in Italy, at the end of March 2020, the average age of those who died among 355 patients with Covid-19 was 79.5 years old. However, 30% had cardiovascular disease, 35% diabetes, 20% active cancer, 24.5% atrial fibrillation and 10% had a history of stroke. Only 1% had no disease other than Covid-19, when 25% had another, 26% had two and 48.5% three or more. A similar observation was made in China, with the same hierarchy in comorbid factors.
The analysis of the first deaths in France seems to follow a similar distribution, with a tiny risk of death for those under 45 without associated diseases (mortality rate less than 0.2%), and a very high risk beyond that. 80 years old, an age when many pathologies (cardiovascular or hematological disease, renal failure, etc.) often limit the ability to defend oneself against infection. In addition, according to the first data from a national register, 83% of intensive care patients are overweight
Finally, in the United States, data from a sample representing 10% of the population revealed on March 28 that 58% of patients are over 65 years old, 31% between 50 and 64 years old and 11% between 18 and 49 years old. And nearly 90% of people hospitalized have associated illnesses, obesity constituting the main factor of hospitalization for those under 50, while those over 65 tend to suffer from hypertension and cardiovascular disease.
In summary, analysis of the prevalence of co-morbidities in patients infected with SARS-CoV-2 shows that different underlying diseases, including hypertension, diseases of the respiratory system, and cardiovascular disease, increase the risk of have a more severe form of Covid-19. However, we know that in the long term, exposure to nitrogen dioxide (NO2) can generate a wide range of health problems, such as hypertension, diabetes, and cardiovascular disease.
In fact, according to recent analysis of NO2 pollution and the number of deaths from Covid-19 in 66 administrative regions of Italy, Spain, France and Germany, this prolonged exposure also increases the risk of mortality following infection by the SARS-CoV-2.
A worrying progression
Like diabetes and obesity, chronic diseases are on the rise all over the world. These two pathologies, which are also pandemics, in themselves constitute risk factors for other chronic diet-related illnesses, while worsening the prognosis in case of seasonal flu or Covid-19. And we know that asthma, the most common chronic disease in children, is a comorbid factor for influenza A (H1N1) virus.
For the most part, these diseases are more common as we get older. But the increase in their prevalence affects all age groups. The number of people with diabetes is therefore increasing mainly in the 45-75 age group, and the same dynamic is observed for cancer, polyarthritis, coronary heart disease, etc. As for Crohn’s disease and spondyloarthritis, it is among the youngest that their prevalence increases the most. Finally, more present in children and young adults in many countries of the world,asthma has seen its prevalence increase by 11% in France between 2005 and 2012.
Incidence of type 2 diabetes in France between 1997 and 2014 according to age groups. (source: French Institute for Public Health Surveillance, IVS)Author provided
In the United States, over 60% of the adult population suffers from at least one chronic disease. And in France, in the space of seven years, from 2008 to 2015, the number of people concerned increased from 8.3 to 10.1 million, or 18% of the population. Diabetes is predominant there : it affects more than 3.3 million people, 42% of whom are under 65 years old. As for obesity, it is present in 17% of French people. However, both diseases are on the rise. There are 150 million obese children today in the world and there could be 250 million by 2030. And the number of cases of diabetes (types 1 and 2) is expected to explode in the world. globe: it could reach 370 million people in 2030 (an increase of 110% in thirty years).
Ultimately, if age increases the risk of complications in the event of an infectious disease, this risk is increased independently of age by chronic diseases such as diabetes, obesity, or even pathologies of the heart and vessels. In addition, studies have shown the existence of a link with infectious diseases such as dengue fever, malaria, AIDS or tuberculosis. Finally, we know that these chronic diseases are associated with regular and / or excessive consumption of ultra-processed foods and to nutritional imbalances. It is therefore necessary to encourage as much as possible a quality diet: we could thus reduce the comorbidities associated with Covid-19, while preventing the progression of chronic diseases.
Michel duru, Research Director at INRAE; UMR AGIR (Agroecology, innovations and territories), Inrae; Anthony Fardet, Researcher, UMR 1019 – Human Nutrition Unit, University of Clermont-Auvergne, Inrae and Edmond Rock, Research Director, Inrae This article is republished from The Conversation under a Creative Commons license. Read the original article.