I take 400 mgs magnesium. I originally was told I needed it for my heart because I had Afib and if I didn’t have 800 mgs a day my heart couldn’t beat regularly. I was not healthy then. But after a year it came down to needing only 400mgs. However, my cardiologist keeps an eye on the level since there is too much and not enough. Periodically the levels much be adjusted. It does make a difference as to the smoothness of muscle movement, but it is needed for the heart as well.