When your body is calm and relaxed, your nervous system might help balance your immune system’s fight against inflammation and viruses — like a natural thermostat for your body’s defenses.

People with a higher heart rate variability — which means their heart naturally adjusts well to stress — tend to have less inflammation and stronger antiviral defenses in their immune cells, even when you account for things like age, weight, and lifestyle.

When your body is more relaxed and your heart rate variability is high, your immune cells tend to turn down the volume on inflammation-related genes, even if the number of those cells doesn’t change.

Even if someone is taking medication that blocks certain stress signals in the body, their heart’s natural rhythm patterns still seem to be linked to how their immune genes behave — meaning their body’s relaxation system might directly affect immunity, no matter what the stress drugs are doing.