Vagus nerve: what it means

The vagus nerve is the longest cranial nerve in your body. It runs from the brainstem down to:

• Your neck
• Your chest
• Your heart, lungs and gut

It's the main nerve that calms your body down after a stress response. When it's active:

• Your heart rate slows
• Your breathing eases
• Your digestion settles

Doctors sometimes talk about vagal tone, a rough measure of how well this calming response works. It's usually estimated from how much your heart rate shifts in time with your breathing, a signal called heart rate variability.

The vagus nerve itself isn't the reason PMS or PMDD happens. Both come from how the brain reacts to the normal rise and fall of estrogen and progesterone across the menstrual cycle, especially the drop before a period in the luteal phase.

One study found that general nerve sensitivity, motor and pain thresholds, measured with electrical stimulation rather than a direct test of autonomic or vagal activity, changed across the cycle in 56 women [1]. Sensitivity and motor thresholds were lowest in the days just before a period in both oral contraceptive users and non-users, though the drop in pain threshold showed up only in the oral contraceptive group [1].

This doesn't mean the vagus nerve causes the mood or body changes of PMS or PMDD. It points to the wider network of nerves running your body's automatic responses, including the parts that calm you down, responding differently in the premenstrual days. That's worth knowing if the week before your period feels more physically raw, not just emotionally harder.

Research naming the vagus nerve specifically in PMS or PMDD is limited. Most of what exists looks at the wider network of nerves that run automatic body functions like heart rate and digestion, which the vagus nerve is part of.

One small study tracked a heart rate marker tied to parasympathetic, or vagal, activity across the cycle in 20 women. Across the whole group, the marker barely changed by phase. In the 11 women who had PMS, the pattern looked different [2]:

The study didn't report a direct phase-by-phase comparison between the PMS group and the women without PMS. A lower marker here suggests less flexibility in the body's calming response during those phases, though this study is small and from 1989 [2].

A separate case report found that a different kind of nerve stimulation reduced premenstrual pain attacks in a woman with a rare blood disorder, acute intermittent porphyria [3]. That's not vagus nerve stimulation, and one case doesn't show it would help with PMS or PMDD. For more on what's been studied, see our research summaries.

You don't need a vagus nerve study to use the idea tonight. A few simple actions engage this nerve and can calm your body in a hard moment, even though none of them treat PMDD:

1. Breathe out for longer than you breathe in, aiming for a slow six-count exhale.
2. Splash cold water on your face or hold a cold pack to your cheeks for a few seconds.
3. Hum, sing or gargle, since the vagus nerve runs close to your vocal cords and throat.

If what you're feeling goes beyond the week before your period, pair this with reading about what causes PMDD, and look up related terms like allopregnanolone, a hormone byproduct tied to mood symptoms before a period.

If you want somewhere to slow down before you react, Niyora is a PMS and PMDD support app. Its Moon feature can help you calm down, see a moment from another angle, and draft what you want to say before you send it.