The brain and inflammation: a new look at dementia and depression

For many years, diseases of the brain were seen through different lenses. Neurologists studied neurons, psychiatrists studied symptoms, and immunologists studied the immune system.

Today, these fields are beginning to meet at a common point: inflammation.

More and more research suggests that inflammatory processes may affect the brain as well as the joints, blood vessels and other organs. This perspective is changing the way we understand conditions such as Alzheimer’s disease, cognitive decline and even some mental disorders.

What is brain inflammation?

Inflammation is the body’s natural defence response when it comes under attack. Normally, this mechanism has a protective role and helps keep tissues healthy.

The brain, too, has its own surveillance system. Specialised cells constantly monitor the brain’s environment and step in when injuries, infections or other changes appear that require a biological response.

The problem arises when this activation becomes excessive or persistent. Instead of protecting, chronic inflammation can affect the functioning of neurons and the communication between different regions of the brain.

A new perspective on Alzheimer’s disease

For decades, research into Alzheimer’s disease focused mainly on the build-up of the beta-amyloid and tau proteins.

These mechanisms remain essential for understanding the disease, but recent studies suggest that brain inflammation could be an important link in the progression of the neurodegenerative process.

Some researchers compare this phenomenon to a slow fire: certain biological changes may set off the process, but inflammation can sustain and amplify it over time.

This new perspective has opened promising lines of research and has driven the development of therapies that aim both to reduce the proteins involved and to modulate the brain’s inflammatory response.

Inflammation and mental health

Perhaps more surprisingly, inflammation has also begun to be studied intensively in psychiatry.

In recent years, researchers have observed that some people who suffer from depression have raised levels of certain inflammatory markers. This does not mean that depression is an inflammatory disease, but it suggests that biological and psychological processes are much more closely linked than was previously thought.

This change of perspective is leading to a more complex approach to mental health, in which the brain is seen in the context of the whole body.

The gut-brain axis

The gut, sometimes called “the second brain”, contains more than 100 million neurons and communicates directly with the brain through the vagus nerve, the immune system and chemicals produced by gut bacteria. Research over the last 15 years shows that the gut microbiome influences mental state through several pathways.

What studies show so far:

• in animal studies, changes in the gut flora can induce behaviours similar to depression or anxiety;
• in some studies, patients with depression have, on average, reduced microbiome diversity;
• interventions on the microbiome (specific probiotics, dietary changes) have shown modest effects on depressive symptoms in some research.

What remains to be clarified

This research is promising, but still a long way from reliable clinical application:

• there are not yet any clinical microbiome tests that can guide treatment decisions;
• “psychobiotics” (probiotics with an effect on mental state) are still at the research stage, with no precise clinical indications;
• the links found so far are associations, and causality sometimes remains unclear.

What comes next?

Alongside the question “what happens to the neurons?”, neuroscience now increasingly asks a new one: “how does the brain’s immune system react?”

The answer could influence future treatments for dementia and the way we understand mental health as a whole.

Can lifestyle influence inflammation?

Recent research also shows that certain daily habits seem to influence inflammatory processes in the body.

Among the factors associated with better brain health are:

• regular physical activity;
• good-quality sleep;
• a Mediterranean-style diet;
• control of blood pressure and diabetes;
• maintaining social relationships;
• constant intellectual stimulation.

None of these factors can guarantee the prevention of a neurodegenerative disease. Together, however, they help create a biological environment that is more favourable to the brain in the long term, and brain health begins long before symptoms appear.

If you notice changes in your memory, or a low mood that doesn’t lift, a specialist assessment can clarify what is going on.