As the American Brain Foundation reports, a growing body of research highlights the critical role of neuroinflammation – the brain’s immune response – in a surprisingly wide range of neurological conditions, impacting over 600 diseases. Frequently enough subtle and difficult to detect, chronic neuroinflammation can significantly compromise brain health at any age. This article explores the complexities of neuroinflammation, its potential causes and warning signs, and what experts are saying about protecting our brains from its damaging effects.
Neuroinflammation, the brain’s immune response to injury, infection, or disease, has been identified as a common factor in over 600 neurological conditions, according to the American Brain Foundation. Understanding this often-overlooked process is crucial, as it impacts brain health throughout life and can contribute to a wide range of illnesses.
While this process is essential for tissue repair, neuroinflammation can be difficult to detect. When it becomes chronic, it poses a significant risk to brain health at all stages of life. Recognizing the warning signs and adopting strategies for brain care is fundamental to preventing and reducing its impact.
Jorge Correale, MD, head of the Neurology Department and Neuroimmunology at FLENI, explained that neuroinflammation “is a reaction of the nervous system’s own defense system, or of circulating inflammatory cells that can penetrate the nervous system.”
He further clarified that this occurs when these cell groups are activated to respond to an aggression, such as an infection, prolonged stress, or a traumatic brain injury. “Under normal conditions, this response is useful and protective. The problem arises when the inflammation persists over time or is very intense. In that case, the brain does not function optimally,” Dr. Correale warned.
When inflammation persists in the brain, two main phenomena can occur, Dr. Correale explained:
- Communication between neurons is disrupted.
- The balance of brain chemicals that regulate mood changes.
As a result, processes like learning and memory can be affected. “Therefore, neuroinflammation has been linked to depression and anxiety, memory and concentration problems, mental fatigue, and an increased risk of neurodegenerative diseases,” Dr. Correale said.
He added, “However, it should be mentioned that in not all pathological conditions is neuroinflammation the cause, but sometimes it is a consequence. The process of alteration of mood, memory or learning occurs due to an intrinsic process of the brain that secondarily conditions an inflammatory process.”
Matías Alet, MD, neurologist and director of Neurology at the Ibero-American Public Health Foundation (FISF), explained that just as the body activates inflammatory mechanisms in response to an aggression, the nervous system can also activate a local immune response to protect itself and repair damage.
“In the short term, this can be helpful. The problem arises when that response becomes excessive, prolonged, or remains ‘switched on’: in those cases it can interfere with the functioning of neural networks that regulate mood, sleep, energy, attention, and memory,” he said.
The American Brain Foundation stated that unlike visible inflammation that occurs on the skin, indicators of brain inflammation cannot be directly perceived.
For example, if a person cuts their finger, they may feel pain, heat, and swelling in the area, because immune cells neutralize foreign bacteria or other infections and repair the tissue. At that time, inflammation is a positive healing process. This healing also occurs in the brain, the American Brain Foundation explained, and is called neuroinflammation.
Dr. Alet noted that regarding the link between mental health and cognition, inflammation may be related to symptoms of depression, anxiety, irritability, persistent fatigue, and cognitive difficulties, especially in certain subgroups of people.
“This does not mean that depression or anxiety are just ‘inflammation,’ nor that there is a single cause. Rather, it is a phenomenon that can act as a contributing factor, interacting with chronic stress, poor sleep, a sedentary lifestyle, metabolic diseases, and, in some cases, with neurological or neurodegenerative processes. The key idea is that the brain and body communicate constantly, and brain health depends a lot on the overall balance of the organism,” he emphasized.
According to the American Brain Foundation, the scope of neuroinflammation is broad. It is also involved in diseases such as Alzheimer’s, Parkinson’s, Huntington’s, multiple sclerosis, encephalitis, stroke, amyotrophic lateral sclerosis, schizophrenia, brain tumors, epilepsy, migraines, myopathy, neuropathy, meningitis, chronic pain, and brain conditions associated with COVID-19.
These pathologies affect 60% of the population in the United States and at least 3 billion people worldwide, compromising essential functions such as thinking, speech, emotion, and movement.
The American Brain Foundation indicated that in the central nervous system, nearly 70% of cells are not neurons, but glial cells. Among them, microglia and reactive astrocytes play a key role in the brain’s immune response. Astrocytes are the most abundant cells in the brain, responsible for regulating communication between neurons and contributing to the maintenance of the blood-brain barrier, according to Johns Hopkins University.
Microglia act as sentinels against injury or infection, while astrocytes regulate blood flow and chemical levels to promote healing. If the initial immune response fails to eliminate the threat, these cells trigger a more intense reaction, which can lead to chronic neuroinflammation.
Brain aging is closely linked to neuroinflammation. Dr. David Dodick, former president of the American Brain Foundation Board of Directors, noted in an American Brain Foundation article that “inflammation causes aging of the joints, muscles, heart, and brain.”
According to Dodick, when the immune system becomes dysregulated or overactivated, normal brain tissue is exposed to damage. “Think of it as ‘inflammatory aging’: aging caused by inflammation. Brain connections are affected. At first you may not notice it, but over time you will,” he warned.
Dr. Correale explained that neuroinflammation does not have a single clear symptom, but a set of signals that usually appear together: “Difficulty concentrating, frequent forgetfulness, a feeling of ‘slow’ or foggy mind. During the COVID-19 pandemic, when cases were prolonged, this symptom was referred to as ‘brain fog.’”
He added, “At the emotional level, it may present as persistent sadness, anxiety or irritability, and lack of motivation. Of course, it may have a physical impact characterized by persistent fatigue, difficulty falling asleep, or headaches.”
Dr. Alet emphasized that many manifestations are nonspecific and may be due to different causes. “However, there are signals that it is convenient to recognize, especially if they are new, persistent or progressive.”
He added to those cited by Dr. Correale: “Persistent fatigue, changes in mood (irritability, anxiety, apathy or sadness), insomnia or non-restorative sleep, new or different pattern headaches, lower tolerance to stress, decreased daily performance (work/study), and in some cases associated neurological symptoms (for example, clumsiness, instability, sensory changes), which always require faster evaluation.”
