Magnesium is an essential mineral, meaning that it is not produced by the body but instead has to be consumed through food or supplements. Magnesium is involved in many reactions and pathways in the body, such as energy production, protein synthesis, muscle and nerve function, blood glucose control, and blood pressure regulation. Magnesium deficiency has been linked to an increased risk of heart disease, osteoporosis, high blood pressure, and type 2 diabetes.

Research indicates that magnesium decreases the risk of forming calcium oxalate kidney stones because it reduces oxalate absorption. Magnesium competes with calcium to bind with oxalate in the gut and the urine. Magnesium is therefore considered a “stone inhibitor” because it decreases the ability of calcium oxalate crystals to form into larger kidney stones.

Magnesium is naturally found in green leafy vegetables such as spinach, whole grains (bran and shredded wheat cereals, brown rice, whole wheat bread), beans, legumes, nuts, and seeds. While most magnesium rich foods are considered healthful, increasing how much you eat of these foods may conflict with other recommendations. Foods that are good sources of magnesium are often rich in oxalate, which your doctor may have advised you to limit. For this reason, taking a magnesium supplement is a better option for most people that have a history of calcium oxalate kidney stones.

Magnesium is available in dietary supplements as magnesium oxide, citrate, chloride, or hydroxide, and is also found in some prescription medications. Even though magnesium is found in many foods, a large U.S. survey found that nearly 50 % of adults had inadequate magnesium intake, with adults over 50 consuming less magnesium than younger adults. These findings indicate that slight magnesium deficiency may be relatively common in the U.S.

Researchers are still trying to determine the best form of magnesium to take. Magnesium citrate is known to be well absorbed, and it has the added benefit of citrate (also discussed in this chapter), another stone inhibitor. Other forms of magnesium have also shown benefit. Both magnesium citrate and magnesium oxide have been shown to decrease oxalate absorption, increase the levels of magnesium and citrate in the urine, and decrease the saturation of calcium oxalate in the urine, which are all positive effects for someone who is prone to forming calcium oxalate stones. Both forms of magnesium worked best when taken with food.

Magnesium from food is well tolerated, but high-dose supplements (>400 mg) can cause stomach upset, nausea, diarrhea, and vomiting. It is important to always take magnesium supplements with food, stay within the recommended doses, and choose an extended release formulation to decrease the risk of these gastrointestinal symptoms.

Potassium is an essential mineral and electrolyte that plays a role in many bodily functions including acid-base balance, nerve transmission, muscle contraction, and many others. The richest food sources of potassium are fruits and vegetables. Potassium can also be found in dietary supplements in low doses (up to 99 mg per serving). Higher doses of potassium exist in the form of prescription medications (for more information, see Chap. 19). Potassium citrate is the form recommended for people who have had kidney stones.

Studies have found that men and women with high potassium diets are less likely to form kidney stones than those whose diets are low in potassium. Potassium citrate (from a supplement or prescription medication) increases levels of citrate in the urine and helps decrease the risk of calcium stone formation. High-dose potassium citrate is also beneficial for uric acid stone formers because it alkalinizes (increases the pH of) the urine, helping to decrease the recurrence of stones.