There’s a big connection between your neurotransmitters and your immune system—particularly what are known as inflammatory cytokines: signaling molecules released by the immune system that trigger actions of other cells towards healing. Here’s how it works.

First: What Inflammation Is

Inflammation is what happens when you body gets damaged. This can be from injury, from chemical exposure, or just a buildup of metabolic waste products that haven’t been properly eliminated. In the case of cardiovascular disease, damage to the vessel lining can come from smoking, from excessive sugar, or from oxidized LDL, to name a few.

In response to the damage, the body releases inflammatory cytokines, most of which start with the prefixes IL (IL-1B, IL-3, IL-4, IL-6, IL-17) or TNF-Alpha… it depends on the type of damage that’s occurred.

In response to these cytokines, the body releases what are known as Reactive Oxygen Species (ROS): these are forms of oxygen, like peroxides, superoxide, hydroxyl, and singlet oxygen atoms. They’re basically oxygen atoms or molecules containing an unpaired electron. All electrons want a buddy; they’re happy when they’re paired up and they become highly reactive, or pro-oxidants (as opposed to antioxidants) when they’re not. These ROS are designed to inflict oxidative damage upon foreign invaders. The problem comes in when they inflict this damage upon your body’s own tissues.

The Depression / Inflammation Connection

When you have excessive oxidative stress on your own tissues, it will deplete your body’s own antioxidant stores, including glutathione, Vitamin C, selenium, and—guess what? Serotonin and norepinephrine.

Just as a reminder, serotonin is the neurotransmitter, or signaling molecule in the brain, most associated with a positive and relaxed mood. Norepinephrine becomes epinephrine, and they, together with dopamine, are the catecholamines: the neurotransmitters associated with the “sparkle” or excitement in life.

What this means: as inflammation goes up, happy neurotransmitters go down. This can make you depressed. But that’s not all it can do.

Low Serotonin, Norepinephrine, and the Cardiovascular System

Aside from its mood effects, serotonin has been found to increase the release of nitric oxide in the endothelial lining (the lining of the blood vessels), leading to relaxation of the vessels. It also directly lowers inflammatory cytokines connected to cardiovascular disease. This means low serotonin would likely have the opposite effect: constricted vessels (hypertension, possible vasospasm) and inflammatory cytokines, which can trigger plaque formation.

Aside from its mood effects, norepinephrine suppresses some pro-inflammatory cytokines such as TNF-Alpha and IL-1B, and encourages expression of anti-inflammatory molecules. This means deficiency can have a net inflammatory effect in the cardiovascular system.

The Upshot

According to the American Heart Association, “the preponderance of evidence supports the recommendation that the American Heart Association should elevate depression to the status of a risk factor for adverse medical outcomes in patients with acute coronary syndrome.”

This is because low serotonin and low catecholamines are linked to depression, and also to cardiovascular disease. Therefore, depression itself can be a symptom of cardiovascular disease, and perhaps can even be caused by underlying inflammation in the cardiovascular system.

What this means: if you’re depressed, and you’ve ruled out other causes (circumstances, toxic thinking, low adrenal function, hormone imbalance, genetics, etc), I suggest checking inflammatory markers for the cardiovascular system, listed here.