I don't know. Says here that the UL (Tolerable Upper Intake Limit) for magnesium is 350 mgs. from supplements: https://www.hsph.harvard.edu/nutritionsource/magnesium/#:~:text=RDA: The Recommended Dietary Allowance,lactation, 310-320 mg. Perhaps in your circumstances a higher dose may be indicated because of your AFib. Just curious, is your diet high in magnesium-rich whole foods?
If a person is under medical care and taking a supplement as part of their treatment- as Capt Obvious has indicated in regard to magnesium - then the requirements or limits of magnesium should and most likely is based on the results of a persons magnesium blood levels. Websites and general guidance for people are fine for the casual supplement taker. Lots of people have absorption problems and many supplements are notoriously difficult to absorb. The blood test resolves much of that. If there is no deficiency because the serum levels are fine, so be it. No need for supplement. On the other hand if you have to take three times as much as the average person to get your your blood levels within the zone, so be it as well. That may be why his doctor prescribed more- because he could see that his magnesium level was low and that he was going to monitor it but start with higher dose to bring it up. or some such scenario. with medical conditions. do the science.
Well your usual approach, as a Canadian, is to see what the usual dose is for a moose and then divide by sixteen for humans which is not necessarily all that accurate. I was reacting to your link saying what tolerable limits are. And saying that that is fine for general chit-chat. Otherwise. follow the blood test. But my comments were for Capt O's benefit. We already know that you know everything or so you say anyway.
You referred to the blood test requirement where? I do confess to not reading your posts, so direct me to that.
I'm on 800mg daily at the recommendation of my cardiologist. Here's the problem with magnesium, most of it is not absorbed into our system and is just passed out through the bowel. Yes, you can get a higher quality magnesium supplement, but even then much of it is just passed through, so 800mg isn't really 800 going into your system. As to a diet rich in magnesium, which I try to maintain, you'll find that our food supply doesn't have the magnesium in it that is used to due to the soil being depleted over the past decades. Add it all up and you need 3 to 4 times the daily minimum just to get close to that minimum. Magnesium is important to regulate heart rhythm among other things. The typical worst side effect most people will experience is loose bowels. Magnesium is a natural laxative. It would be a good guess that unless a person is supplementing magnesium they are probably deficient, especially if they have an active/fitness type lifestyle.
If the laxative effect becomes problematic then use magnesium glycinate and you can color that problem gone. Readily available.
As a side note, I'm sure Freddy was not trying to be confrontational. We both have come to check our political differences at the door of this particular forum. Might take a good natured jab ever now and then, but the vitriol of the political realm is not present. He and I take health and fitness seriously, as I'm sure you do. Anything I post here in this forum can be taken as my honest opinion and experience, and I'm always willing to learn from others on this subject. Freddy is knowledgeable on heath and fitness and I respect his experience and opinions, as I do yours, or anyone else in this forum. Just an FYI.