Excessive caffeine consumption has been associated with arrhythmia in human studies. Although most people do not experience arrhythmia as a result of caffeine consumption,¹ some healthy people appear to be susceptible to as little as one cup of coffee.²

Allergic reactions to foods and environmental chemicals have been reported to trigger arrhythmias.³ Consultation with a physician may help to pinpoint these sensitivities.

A double-blind trial investigated the effect of oral magnesium supplementation on arrhythmic episodes in people with congestive heart failure. Those people taking 3.2 grams per day of magnesium chloride (equivalent to 384 mg per day of elemental magnesium) had between 23% and 52% fewer occurrences of specific types of arrhythmia during the six-week study, compared with those taking placebo.⁴ Lower serum concentrations of magnesium were found to be associated with a higher incidence of arrhythmia in a large population study.⁵ The anti-arrhythmic properties of magnesium appear to be specific. For example, magnesium is clearly able to prevent a drug-induced arrhythmia called torsade de pointes,⁶ but it does not appear to prevent atrial fibrillation.⁷ A doctor should supervise any use of magnesium for cardiac arrhythmia.

In a double-blind trial, people with a type of arrhythmia known as ventricular premature complexes were supplemented for 16 weeks with either 15 ml (1 tbsp) per day of fish oil or a similar amount of safflower oil as placebo. Patients taking the fish oil had a significantly reduced frequency of abnormal heartbeats compared with those receiving placebo, and 44% of those receiving fish oil experienced at least a 70% reduction in the frequency of abnormal beats.⁸ In a separate study, however, men given 20 ml (4 tsp) of cod liver oil per day for six weeks, beginning one week after a heart attack, had the same frequency of irregular heart beats as did men given no supplemental oil.⁹ In a double-blind study, people who had a history of certain potentially life-threatening arrhythmias—sustained ventricular tachycardia or ventricular fibrillation—had an increase in the recurrence rate of these arrhythmias when they took fish oil.¹⁰ A similar study found no adverse effect of fish oil supplements in people with these serious arrhythmias.¹¹ Because of these conflicting findings, people with a history of either of these arrhythmias should consult a doctor before taking fish oil.

Patients taking hydrochlorothiazide for high blood pressure had a significant reduction in arrhythmias when supplemented with 1 gram twice per day of potassium hydrochloride (supplying 1040 mg per day of elemental potassium). Those results were not improved by adding 500 mg twice per day of magnesium hydroxide (supplying 500 mg per day of elemental magnesium) to the potassium.¹² Low serum concentrations of potassium were found to be associated with a higher incidence of arrhythmia in a large population study.¹³

Three cases have been reported in which ventricular premature beats disappeared after supplementation with copper (4 mg per day in the two cases for which amounts were reported).¹⁴ In one of these people, supplementing with zinc made the arrhythmia worse, confirming previous observations that excessive zinc intake may lead to copper deficiency,¹⁵ which in turn may lead to arrhythmia.

An active constituent in corydalis, dl-tetrahydropalmatine (dl-THP), may exert an anti-arrhythmic action on the heart. This action was observed in a preliminary trial with 33 patients suffering from a specific type of arrhythmia called supraventricular premature beat or SVPB.¹⁶ Each patient took 300 to 600 mg of dl-THP per day in tablet form, and the dl-THP was found to be significantly more effective than placebo in reducing arrhythmia.

An animal study showed that an extract of hawthorn significantly reduced the number of experimentally induced arrhythmias.¹⁷ Although the use of hawthorn for arrhythmia in humans has not been studied scientifically, it traditionally has been used for this purpose.¹⁸

Gross deficiency of dietary selenium may cause many heart problems, including arrhythmia. Based on this finding, one author has theorized that correction of low selenium status may improve many arrhythmias, even in the absence of overt deficiency symptoms.¹⁹ Controlled research is needed to evaluate this possibility.

One case of long-standing sick-sinus syndrome (another type of arrhythmia) was reported to resolve upon supplementation with 800 IU per day of vitamin D prescribed for an unrelated condition. However, it was not clear from that report whether the improvement was due to the vitamin D.²⁰ More research is needed.