Laura,
Do you suffer from Crohn's disease? I have read info sources that say sufferers of Crohn's disease have trouble absorbing Magnesium.
I don't think I have an intestinal disorders except that I used to drink 1/2 gallon of coffee daily. Also, I was once a very heavy drinker, and I would - don't mean to be gross -see mucus in my stools. Also, I was on an extremely high fat/high protein diet.
Now that I am mainly on a plant based diet with just a little meat, I really don't take magnesium citrate to often any more. My stools are already comfortably loose due to all the greens and whole grains that I now consume.
The health industry provides all kinds of disease names for different symptoms. What seems apparent to me is that certain symptoms can have multiple causes. In my case it seemed to be diet and lifestyle that caused me to have the symptoms of AS. I had no symptoms until the age of 43. I am gene negative.
Somewhere I read that health begins in the intestines. Magnesium is a great laxative. Take too much and you will have the runs. But cleaning out my intestines by supplementing with magnesium citrate seems to have been very beneficial to my health. Magnesium relax's muscles and helps you sleep better, among other things.