Came across this little piece in an article on removing Flouride from your water.

How to remove fluoride from your body
Magnesium follows a similar absorption path as fluoride. According to a study by the American Institute of Nutrition, a diet low in magnesium results in a higher concentration of fluoride in the bones – and likely elsewhere. The study concluded: “In summary, it can be stated that in intoxication with fluorine compounds, magnesium plays a protective role by countering and reducing the toxic effects of F-.” (Cerklewski F L. Influence of dietary magnesium on fluoride bioavailability in the rat. American Institute of Nutrition 117 (3) 456-500, 1987)

Most people are magnesium deficient – and not just slightly. Blatantly ignored in modern medicine, magnesium deficiency is rampant, responsible (at least in part) for the increased incidence of heart disease, stroke, diabetes, asthma, arthritis, high blood pressure, chronic fatigue syndrome, attention deficit and many other conditions too numerous to list. Magnesium has been referred to as the “master mineral” because of its involvement in over 300 enzyme systems including protein synthesis, muscle and nerve function, blood glucose control, and blood pressure regulation. Magnesium is required for energy production and for the synthesis of DNA. It also plays a role in the active transport of calcium and potassium across cell membranes, a process that is important to nerve impulse conduction, muscle contraction, and normal heart rhythm.

Unlike many other nutrients that are better supplied in food, water can be an excellent source of magnesium. Approximately 50% of the magnesium contained in mineral water is absorbed. This is greater than the amount absorbed from food. The ‘magnesium-in-water’ effect was identified years ago as beneficial for those on a low magnesium diet. Supplying magnesium in water may be helpful in releasing toxic levels of fluoride accumulated through years of drinking fluoridated water. It may also have numerous other benefits. Read the article on making magnesium bicarbonate water.

Dr. Marc Sircus discussed Magnesium bicarbonate further in his books.