Onions come with quite a reputation. They add bite to your sandwich, wreck your breath and they can make you cry, but many medical professionals recommend it’s consumption, both for stomach health and heart health.
Problem is, some people get cardiac arrhythmia from eating onions. Scan the web up and down and you’ll have a hard time finding a medical website corroborating the idea that onions can cause PVCs, PACs or some other irregular heart rhythm. But the anecdotal evidence is everywhere.
Even so, Doctor Michael Murray suggests eating onion and garlic as part of a heart-healthy diet to prevent arrhythmia.  The Indian Heart Journal recommends garlic be eaten to prevent arrhythmia.  PBS reports that to reduce the chance of arrhythmia people should eat foods with important antioxidants like Quericetin, which is found in onions. The book “Medical Botany” lists onions as a food that reduces oxidative stress and that there’s an inverse relationship between the amount of onion antioxidants in your system and your odds of getting heart disease. They are even being shown to reduce the chance of stomach cancer and pancreatic cancer 
So how is it that so many people claim that onions are the cause of their arrhythmia when so much research points to onions being heart and arrhythmia friendly? There’s evidence that onions can kill dogs. And cattle can develop tachycardia from ingesting onions. But you won’t find a reference indicating a direct link between onions and irregular heart rhythms.
The secret may lie in the vagus nerve. The vagus nerve is a very long and complex pair of cranial nerves that conveys information about your body’s internal organs to your brain. Parasympathetic innervation of the heart is mediated by the vagus nerve. In simple language, there are parts of your nervous system that you have no conscious control over which can excite the heart – the vagus nerve acts to lower your heart rate. Pay attention to your heart rate when you breathe in, then breathe out. Does it slow down when you exhale? Speed up when you inhale? That’s your vagus nerve at work. The degree to which your heart rate changes during each respiratory cycle is the measure of your vagal tone. The greater control your vagus nerve is able to exert on your heart rate, the better it’s supposed to be for your health.
However, while vagal tone prolongs refractory periods in ventricular muscle (thereby making it anti-fibrillatory), the opposite is true for atrial muscle. Vagal tone shortens the refractory period of atrial muscle tissue, promoting the formation of reentrant electrical impulses (wavelets), creating an environment where supraventricular arrhythmias can develop. A study in Sweden showed that 5% of paroxysmal atrial fibrillation patients identified onions as one trigger for their arrhythmia.
Because the vagus nerve also innervates the stomach, it’s possible that a sensitized vagus nerve presented with gastric distress due to spicy foods (like onions) or distension (bloating) from a large meal and/or retained gas, would exert it’s influence on the heart, exciting the muscles in the atrium while calming those in the ventricles, creating a ready environment for palpitations and dysrhythmia.
What may be the best approach to solving this riddle for yourself, after seeing your physician of course, is to keep a food diary. Tracking your food intake by type and quantity along with any corresponding appearance of arrhythmia may give you the insight you need to target those foods triggering your skipping heart and reducing or eliminating them.
- ^ Doctor Murray: Arrhythmias
- ^ Indian Heart Journal: Anti-Arrhythmic Effects of Herbal Medicine
- ^ PBS.org: Second Opinion: Heart Rhythm Disorder
- ^ Medical Botany: Central Nervous System and Psychiatry
- ^ MSNBC: Ward off Cancer with Bad Breath
- ^ CancerNetwork.com: An Onion a Day May Repel Pancreatic Cancer
- ^ Petalia.com: Human Foods that Posion Pets
- ^ Encyclopedia of Clinical Toxicology: Onions
- ^ ClinicalCorrelations.org: Vagally-induced Atrial Fibrillation
- ^ Arrhythmia-provoking factors and symptoms at the onset of paroxysmal atrial fibrillation: A study based on interviews with 100 patients seeking hospital assistance
Woman chopping onions image courtesy of TVLesson.com.