I don't know where you got your information, but it is not accurate. Magnesium supplements are absorbed into the body. They absorb best when taken on an empty stomach, so that the strong stomach acids can assist in absorption. Magnesium deficiency is very common, and when it has been going on for a very long time, then all of the cells in the body will have sub-optimal levels of magnesium in them. Because magnesium is a very large molecule, it takes a lot of work and a long time for every cell in the body to have its proper amount of magnesium restored to it. It can take up to a year to get cellular magnesium levels up to an optimal level, if someone is deficient. Magnesium is a very safe nutrient to take, and estimates are that half of the U.S. population is deficient in magnesium because of fluoridation in many water systems, and depletion of magnesium in agricultural soils that have been depleted of micro-nutrients.