Chris Kresser: think at this point it’s pretty clear that it’s all about nutrient balance. There are some nutrients that have really ridiculously high toxicity thresholds, like vitamin C, where it seems like you can pretty much take it to bowel tolerance, very, very high doses, and it’s not going to cause any problems. But then there are other nutrients that seem to have a much narrower range of tolerability, like iron, I would say, and even vitamin D, which can become toxic at doses that people can easily take. Magnesium, from what I have observed and from the research, I would say, is not the most sensitive nutrient in terms of toxicity, but the symptoms that you would look out for would be nausea and vomiting, lethargy, muscle weakness, irregular heartbeat or arrhythmias, hypotension, as I mentioned, urine retention, any kind of respiratory problem, or in the most severe manifestation, maybe a heart attack. Magnesium works in concert with other nutrients like potassium and sodium. It has a lot of effects on muscle contraction, which explains some of the cardiovascular effects, and it works to regulate blood pressure, which also explains some of the cardiovascular effects.
The recommended intake of magnesium for women is 320 milligrams a day and for men is 420 milligrams per day, but I think well over 60 or 70 percent of people don’t even meet those recommendations, which may be conservative. I think over the long term something like 300 to 400 milligrams of additional magnesium is probably a pretty safe dose as long as people are eating a nutrient-dense diet and getting plenty of the other nutrients. I wouldn’t feel very comfortable with a patient taking something like 800 milligrams of magnesium, which can be done in the short term, for more than maybe a couple of months without testing and supervision and making sure that there aren’t any toxicity symptoms that are happening.