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 pointed out the “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 means of preventing 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, it can result in various immune-mediated inflammatory diseases. However, we know that the innate immune response, the first line of defense against infections, triggers the adaptive immune response. We also know that this first response is at the origin of the inflammatory reaction whose excesses are so feared 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.
Food processing: what we eat shapes our gut microbiota
When the microbiota is disrupted
Several pathologies have been associated with disturbances of 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), joints (rheumatoid arthritis which generates fatigue and joint pain) or the central nervous system (multiple sclerosis and its pain, fatigue, sensory and motor disorders, etc.).
The processes involved combine inflammation, oxidative stress, but also food and the 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 has moved away from the ancestral model. And we can also imagine that the rapid modernization of medical practices (antibiotics, caesarean sections, etc.) have gradually deteriorated it, thus contributing to the spread of various diseases. However, its structure and functions are mainly shaped by diet.
In Western countries, it is characterized by:
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 body and promotes the appearance of various diseases.
It also induces a phenomenon of immunosenescence, that is to say a loss of effectiveness of the immune system, resulting in an increased risk of infections and possible complications. However, this goes hand in hand with changes in the intestinal microbiota.
These changes are partly linked to a less diversified diet. By intervening in the diet of older people using the 3V rule while encouraging them to maintain physical activity, we could therefore 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 as a 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 correctly, hence increased vulnerability to pathogens in the environment.
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 therefore constitute 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 disturbed by the influenza virus produces less short-chain fatty acids, which goes hand in hand with a reduced bactericidal action of cells of the innate defense system in the pulmonary alveoli, resulting in increased susceptibility to secondary bacterial infections. However, when it comes to chronic diseases, the figures of the Covid-19 epidemic are telling …
In Italy, at the end of March 2020, the average age of people 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 the factors of co-morbidities.
The analysis of the first deaths in France seems to follow a similar distribution, with a very low 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 registry, 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 diseases, obesity being the main factor in 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 cause a wide range of health problems, such as hypertension, diabetes, and cardiovascular disease.
In fact, according to recent analysis of NO pollution2 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 with 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, constitute in themselves risk factors for other chronic food-related diseases, while worsening the prognosis in the event of seasonal flu or Covid-19. And we know that asthma, the most common chronic disease in children, is a comorbid factor for the 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 cancers, 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 around the world, asthma has seen its prevalence increase by 11% in France between 2005 and 2012.
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 rose 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 in the world today 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 regardless 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, it is known that these chronic diseases are associated with the regular and / or excessive consumption of ultra-processed foods and with 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
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