Magnesium is an essential nutrient that increases calcium absorption, which means it boosts the beneficial effects of calcium on PMS. Its other functions include regulating muscle contraction and relaxation, regulating blood sugar levels, promoting normal blood pressure, and playing a role in energy metabolism.

A 1999 study in the Journal of Women’s Health found that 200 milligrams a day of magnesium reduced mild PMS-induced fluid retention, breast tenderness, and bloating by 40 percent. The researchers, who administered either a placebo or a magnesium supplement study participants over two menstrual cycles, found there was no difference between the magnesium and the placebo in the first month. In the second month, however, women taking the magnesium had greater reduction in symptoms.

Studies support magnesium’s beneficial effect on PMS. For example, a 1998 study in the American Journal of Obstetrics and Gynecology found that 1,200 milligrams a day of chewable calcium carbonate reduced PMS symptoms such as water retention, food cravings, and pain by 48 percent, while placebo relieved symptoms by only 30 percent. The investigators concluded that “calcium supplementation is simple and effective treatment in premenstrual syndrome, resulting in a major reduction in overall luteal phase symptoms.”

There is also some evidence that magnesium supplementation may reduce the frequency and severity of migraine headaches. Two placebo-controlled studies demonstrated a beneficial effect on migraine, while another placebo-controlled study found no benefit compared to placebo.

Foods high in magnesium include buckwheat, nuts, and whole grains, as well as collard greens, dandelion greens, avocados, sweet corn, cheddar cheese, sunflower seeds, shrimp, dried fruit (figs, apricots, and prunes), and many other common fruits and vegetables.