How much magnesium can you take a day?

Magnesium Intake/day: The food and nutrition board of the institute of medicine has set the acceptable upper intake level for magnesium supplements at 350-400 mg per day, which is the highest level of intake that is not apt to cause diarrhea or other gastrointestinal problems in most people. Your body absorbs between 1/3 and 1/2 of the magnesium you consume. Foods rich in magnesium include green leafy vegetables.