“Almost half of Americans don’t get enough magnesium from their diet. Over time, low levels of the mineral may set the stage for a variety of health issues, including type 2 diabetes, high blood pressure, and migraines. Older adults, alcoholics, and those with type 2 diabetes or digestive issues are more likely to lack it, either because their bodies get rid of too much magnesium or they don’t take in enough in the first place. . . . An adult woman needs about 310 milligrams of magnesium a day, and 320 milligrams after age 30. Pregnant women need an extra 40 milligrams. Adult men under 31 need 400 milligrams and 420 milligrams if they’re older.