It's not clear that they help prevent high blood pressure. These three minerals are important in blood pressure regulation. But there's no evidence that high doses of them from supplements will lower blood pressure and help prevent hypertension. Calcium supplements are a good idea for postmenopausal women, but we strongly suggest that you get some calcium and all your potassium and magnesium from foods, which also contain other nutrients you need. Nonfat or low-fat dairy products are the best sources of calcium, though some leafy greens are good, too.
Potassium is plentiful in most foods.
Magnesium is plentiful in whole grains, leafy greens, meats, milk, beans, bananas, and nuts. If you're on hypertensive medication, your doctor may recommend potassium supplements. Moderate doses have no effect on blood pressure. But caffeine is not known to cause hypertension.