This post focuses on the science behind various neurotransmitters and hormones and their link to vagus nerve activity.
Most of the research has been conducted in animals or cells. We still know little about the interplay between the vagus nerve, hormones, and neurotransmitters in humans.
Our aim is to discuss research findings. We strictly advise against taking any hormones to affect vagus nerve activity.
Thus, serotonin has some mixed effects. 5-HTP is a supplement that may increase serotonin, but it’s unknown whether it affects the vagus nerve.
Mice who had their vagus taken out didn’t exhibit the appetite-reducing effects of oxytocin .
Orexin stimulates the vagus nerve from the brain, which promotes gut flow. It can stimulate the pancreas, too, according to an animal study .
Ghrelin may stimulate the pancreas from the brain via the vagus .
Leptin-resistant animals were hungrier since the vagus nerve became less sensitive to CCK .
However, another study found that leptin effect on the vagus signal doesn’t play a major role in food intake .
More research is needed to clarify these findings.
CRH has variable effects on the vagus nerve. Scientists think it decreases its activity from the brain to the heart. Vagus nerve activation will slow the heart rate, but CRH seems to inhibit this and increases heart rate–at least in animals .
Researchers are investigating whether CRH stimulates the vagus impulse from the brain to the colon (by activating the dorsal nucleus of vagi, via cholinergic transmission) .
Some scientists believe that the vagus nerve may help reduce pain, and this is the proposed mechanism by which estradiol reduces pain in certain circumstances. However, these pathways have not been properly verified in humans .
Besides influencing the release of oxytocin, the vagus nerve is thought to be important for releasing testosterone. Research teams are investigating whether vagus nerve imbalances are connected to low testosterone in some men .
One intriguing study hypothesized that although testosterone can make people more aggressive, this is not the case when the vagus nerve is functioning right. These findings have yet to be replicated .
The vagus nerve may stimulate other hormones such as parathyroid hormone, which is important for the conversion of vitamin D3 to active vitamin D (1,25). A direct influence of the vagus nerve on vitamin D status hasn’t been established, though .
NPY might block some of the vagus nerve effects, according to animal data. NPY is described as an anti-anxiety and hunger-increasing hormone, which prevents heart rate decrease from vagal stimulation. How it impacts vagus nerve stimulation in humans is unknown .