Cardiovascular diseases and cancer are among the leading causes of death in the world, diabetes affects 422 million people and Alzheimer's disease nearly 50 million. All these pathologies initially appear unrelated, but modern science has shown that these epidemiologic coincidences have one same cause: Chronic inflammation. This chronic inflammation, often called as "the silent killer" is now a public health problem because it is indicated in the majority of the most common diseases of our time. How does this phenomenon damage the human body? And how does it lead to all these diseases?
How does inflammation damage the human body?
There are many bad lifestyle habits like consuming a lot of refined sugar and bad fats, not exercising or stressing a lot. The common point between them is that they all unnecessarily and chronically stimulate the "mediators of inflammation" in our body. Inflammation is an important pillar of our immune system and allows our survival. Whether through a burn, a cut, an infection, any damage to our body leads to the results we know: a redness of the skin, which becomes hot, painful and swollen. Those four symptoms that characterize inflammation are the result of a panoply of physiological reactions.
Usually called in case of emergency, inflammation can also cause serious damage to our organs and many diseases if it is activated chronically. Now, doctors and researchers are pointing to chronic inflammation as a major risk factor for many pathologies, including heart disease, cancer and type II diabetes.
If a high level of bad cholesterol in the blood increases the risk of cardiovascular disease, it does not explain all the physiopathology of atherosclerosis. Indeed, half of the heart attacks occur in people who have normal or low cholesterol. Although present in small amounts, cholesterol that adheres to the walls of blood vessels attracts mediators of inflammation. In a person whose inflammation is stimulated excessively, plaques form more easily. Over time, they may create a clot, increasing the chances of heart attacks and strokes. Another discovery of impact revealed the implication of chronic inflammation in cancerous diseases: procreative agents, such as chemicals, ultraviolet rays or certain infections, would cause cancer by stimulating inflammatory mechanisms. This state of chronic inflammation helps protecting young cancer cells. For example, some substances released by immune cells during inflammation, such as free radicals, would help them become immortal.
Inflammatory processes would also be directly linked to type II diabetes. Currently, it is known that people who have a high degree of inflammation markers (C-reactive protein, interleukin-6) have an increased risk of developing this disease. These mediators interfere with the signals of insulin, which gradually prevents cells from absorbing blood sugar. The fat cells would also produce mediators of inflammation. By recognizing the role of inflammation in the development of these widespread diseases, scientists are laying the groundwork for new strategies for prevention and health promotion.
The main diseases caused by chronic inflammation:
Neurodegenerative diseases:
Chronic inflammation destroys neurons gradually. In animals, studies have confirmed that inflammation in the brain leads to neurodegeneration and accelerates the progression of diseases related to neuronal regression. At the end of 2017, US researchers have shown that in 1,600 long-term patients, high levels of inflammation were associated with cerebral narrowing (commonly known as age-related cerebral atrophy). Neurodegeneration is also the main factor causing Alzheimer's disease.
Type II diabetes: Chronic inflammation promotes insulin resistance in our muscles. When they overload, the fat cells secrete molecules that will attract immune cells and trigger an inflammatory reaction promoting insulin resistance, in the adipose tissue but also in the muscles. Indeed, following prolonged insulin stimulation for lipogenesis needs, the body gradually becomes resistant to insulin and type 2 diabetes occurs. Psychiatric diseases: Chronic inflammation inhibits a normal inter-neuronal communication. This is one of the most studied scenarios for schizophrenia. Several studies assume that a maternally acquired disease during pregnancy is the trigger for an inflammation that would then result in low-grade inflammation. The brain of the future child would grow in this inflammatory environment, which would disrupt the functioning of neurotransmitters, and cause different psychiatric diseases. Cardiovascular diseases: As a matter of fact, chronic inflammation, as well as bad cholesterol and hypertension, has been recognized as one of the factors causing cardiovascular diseases, such as strokes, heart attacks, hypertension and heart failure.
Anyone with a chronic inflammation has a higher risk of cardiovascular problems compared to the rest of the population. Indeed, inflammation makes the atheromatous plaques of the blood network more vulnerable.
Chronic inflammation weakens the vessel wall. At some points in our vessels - bends, bifurcations - turbulence creates inflammation of the cells of the vascular wall. This phenomenon make these vessels’ walls permeable to certain lipids such as bad cholesterol (LDL), which get trapped, oxidize and trigger an immune reaction. Immune cells enter the wall and remain stuck in it, helping to both intensify the inflammatory response and enlarge the atheroma plaque, which can later break, causing a clot. These clots are responsible of vascular accidents like strokes or heart attacks that can be fatal. Cancer: Chronic inflammation is the ally of cancer cells. In diabetics, insulin resistance (itself nourished by inflammation) is also suspected of promoting the appearance of mutations in cells causing tumors. Some inflammatory diseases are known to increase the risk of cancer. Moreover, in patients with cancer, there is a higher level of TNFα, a pro-inflammatory cytokine. However, the links between cancer and inflammation are probably more complex. Because once the tumor is established, "the tumor cells manage to deflect the immune system. They themselves secrete cytokines and modify the phenotype of macrophages (immune cells) to prevent them from attacking tumor cells. Conclusion: Chronic inflammation is often insidious and develops without visible signs, but creates a climate that disrupts the functioning of cells in the inflamed environment. Although less spectacular and without apparent symptoms, this type of inflammation represents a medical problem of great importance because it is now well documented that the development of most chronic diseases that affect our society (cardiovascular disease, diabetes-type 2, several cancers) is favored by the presence of these chronic inflammatory conditions.
