Michel Duru, Inrae; Anthony Fardet, Inrae and Edmond Rock, Inrae
If thanks to hygiene measures, vaccines and antibiotics, the mortality linked to infections has been decreasing in recent years, chronic noncommunicable diseases have seen their incidence increase. However, among the main defendants, finger pointing is the “junk food” which generates overweight, obesity and associated pathologies. In addition, it is now known that obesity and diabetes increase the risk of contracting a severe form of Covid-19. Clearly, eating better is a means of preventing chronic noncommunicable diseases, but also infectious pathologies. And it goes through the gut microbiota filter.
This community of microorganisms has a key role in our health. Over time, a real 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. 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, the excesses of which are so feared in the case 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 secondary infection by bacteria), or even a disease chronic.
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When the microbiota is disturbed
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), the 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 suggest that in our industrialized societies, the gut microbiota has moved away from the ancestral model. And one can also imagine that the rapid modernization of medical practices (antibiotics, cesareans …) has gradually deteriorated, 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:
Based on this observation, we can suppose that a diet respecting the rule of 3V (true, vegetable and varied), with on the one hand more fiber and antioxidant intakes, and on the other hand less contaminants, allows reduce the risk of developing chronic diseases due to better functioning of our immune system. Such a diet is similar to 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 indicators of an aging population in Europe are correlated with the local intensity of the epidemic. We can easily explain it. Aging, in fact, results in the development of low-noise inflammation that weakens the body and promotes the appearance of various diseases.
It also induces an immunosenescence phenomenon, that is to say a loss of efficiency of the immune system, hence an increased risk of infections and possible complications. This goes hand in hand with modifications of the intestinal microbiota.
These changes are partly related to a less diversified diet. By intervening on the diet of the elderly 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 barrier role against pathogens. But if, for various reasons – such as taking antibiotics or an unbalanced diet – its balance is impaired, then the microbiota no longer fulfills its role properly, resulting in increased vulnerability to environmental pathogens.
The impact of chronic diseases
Chronic diseases are themselves largely associated with such imbalances or poor adaptation of the intestinal microbiota (or dysbiosis), so they constitute a risk factor for complications following a viral infection. Besides, we know that secondary bacterial infections often complicate viral infections. And it could be that this secondary infection is explained by the alteration of the microbiota induced by the initial infectious disease: this 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 an increased sensitivity to bacterial infections. When it comes to chronic diseases, the figures for the Covid-19 epidemic speak for themselves …
In Italy, at the end of March 2020, the average age of the deceased among 355 patients with Covid-19 was 79.5 years. However, 30% had cardiovascular disease, 35% had diabetes, 20% had active cancer, 24.5% had 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 comorbidities.
The analysis of the first deaths in France seems to obey 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 significant risk beyond 80 years old, 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 resuscitation 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 almost 90% of people hospitalized have associated illnesses, obesity being the main factor in hospitalization for those under 50, when those over 65 suffer more from hypertension and cardiovascular disease.
In summary, an analysis of the prevalence of comorbidities in patients infected with SARS-CoV-2 shows that various underlying diseases, including hypertension, diseases of the respiratory system and cardiovascular diseases, increase the risk of have a more severe form of Covid-19. However, we know that over 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 death following an infection by SARS-CoV-2 .
A disturbing progression
Like diabetes and obesity, chronic diseases are spreading worldwide. These two conditions, which are also pandemics, are in themselves risk factors for other chronic food-related illnesses, while worsening the prognosis for seasonal flu or Covid-19. And we know that asthma, the most common chronic illness in children, is a comorbid factor for the influenza A (H1N1) virus.
For the most part, these diseases are more common as we age. But the increase in their prevalence affects all age groups. The number of people with diabetes thus increases mainly in the 45-75 age group, and the same dynamics are observed for cancers, polyarthritis, coronary heart diseases, etc. As for Crohn’s disease and spondyloarthritis, the prevalence increases most among the youngest. Finally, more prevalent in children and young adults in many countries of the world, asthma saw its prevalence increase by 11% in France between 2005 and 2012.
In the United States, more than 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 affected 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 of age. As for obesity, it is present in 17% of French people. Both diseases are on the increase. There are now 150 million obese children worldwide and there could be 250 million in 2030. And we expect an explosion in the number of cases of diabetes (types 1 and 2) 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 pathologies of the heart and vessels. In addition, studies have shown a link with infectious diseases such as dengue, malaria, AIDS or tuberculosis. Finally, we know that these chronic diseases are associated with regular and / or excessive consumption of ultra-processed foods and nutritional imbalances. Quality nutrition should therefore be encouraged as much as possible: this could 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.