Thinner Vagus Nerve Linked to Faster Heart Rate in Older Adults

The work was published in PLoS One in 2026. It is an observational, crosssectional study in people, which means it looked at one point in time. It can show links between measurements. It cannot show that one thing causes another. The analysis included 183 community-dwelling adults aged 65 and older.

The participants come from the YAHABA study, a cohort that began in 2016 in Yahaba, Iwate, Japan. It follows people aged 65 and over, with a focus on neurological disease. The data here come from a follow-up survey in early 2023. Of 202 people who had both a neck ultrasound and a 12-lead electrocardiogram (ECG), 183 were analysed. Researchers excluded those with a pacemaker, atrial fibrillation on the ECG, or missing height or weight data.

The vagus nerve is the main nerve of the parasympathetic system, the part of the body's automatic control that helps calm it down. Earlier work, described in the paper's introduction, used electrical stimulation of the nerve in animals and in patients with heart failure. Right-sided stimulation mainly lowered heart rate. Leftsided stimulation in animals tended to cause a conduction block between the heart's upper and lower chambers. What remained unclear was whether the physical size of the nerve itself relates to the heart's electrical activity.

To test this, the team measured the cross-sectional area of each vagus nerve at the level of the thyroid, using a carotid ultrasound. The median area was 1.00 square millimetres on the right and 0.90 on the left. The two sides were only weakly correlated. The researchers then split each side into three groups, called tertiles, from thinnest to thickest. The groups were not exactly equal in size: on the right they held 61, 70 and 52 people, and on the left 52, 74 and 57, because the cut-offs fell on measurement steps of 0.1 square millimetres. They compared ECG readings across the groups, adjusting for age, sex, height, weight and use of medicines that affect the heart's electrical activity.

On the right side, the thinnest group had a higher heart rate than the middle group (p = 0.021). They also had a shorter interval between heartbeats (p = 0.037) and a higher P-wave amplitude (p = 0.008). The P wave reflects electrical activity in the upper chambers of the heart. The thinnest group did not differ significantly from the thickest group. So the pattern was not a simple step from thin to thick.

On the left side, the tertile comparisons showed no significant differences. In a separate regression analysis that treated nerve size as a continuous number, the left nerve's area was associated with QRS duration (p = 0.038). QRS duration reflects how long it takes electrical signals to spread through the lower chambers. The right nerve's area showed no significant link to any ECG measure in that analysis.

From this, the authors suggest that the right vagus nerve may relate to electrical activity in the heart's natural pacemaker and upper chambers, and the left to the lower chambers. This is their interpretation, and the study did not test it directly.

There are clear limits. The study is cross-sectional, so it cannot tell whether a thinner nerve leads to a faster heart rate, or the reverse, or whether something else explains both. Measurement reliability was only moderate, at about 0.6 for repeat readings by the same and by different raters. ECG conditions were not standardised across participants. The sample was modest, and the findings came from older adults in one Japanese town. The significant results were few, with p-values close to the 0.05 threshold in some cases, and the middle-versus-thinnest pattern was not matched by the thickest group. This is the weakest part of the argument.

For now, the finding adds to evidence that the vagus nerve is a physical structure that can be seen and measured, and that its size may carry information about heart function in later life. Whether tracking it would help anyone is unknown. What to watch next is long-term follow-up of the YAHABA cohort, which could show whether changes in vagus nerve size over time go together with changes in heart rhythm or heart health.

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