Low serum magnesium levels have been correlated with a risk of AFIB in both the ARIC and Framingham studies.
There are also data that US population as a whole is deficient in magnesium. Here is an excellent review article on magnesium and its role in cardiovascular disease.
There are data that magnesium supplementation may reduce risk of AFIB in post-bypass surgery patients. Magnesium supplementation may help control heart rates when patients present with atrial fibrillation – however we don’t use magnesium routinely for rate control since better drugs are available. Magnesium supplementation has not been shown to improve the success of cardioversion.
Low magnesium levels can lead to life threatening arrhythmia called torsades de pointes (a type of ventricular arrhythmia).
However there is NO DATA that supplementing magnesium will reduce risk of atrial fibrillation or will help in management of atrial fibrillation.
I do routinely check serum magnesium levels in patients with atrial fibrillation and supplement magnesium if levels are low. For patients who have normal serum magnesium levels, I do not recommend magnesium supplements but ask them to take a diet rich in magnesium – whole wheat, spinach, nuts (almonds, cashews, peanuts), tofu, black beans, avocado, edemame.