Harvard Health Letter

Key minerals to help control blood pressure

It's usually best to get calcium, magnesium, and potassium from food. Are you getting enough?

A healthy, balanced diet plays a major role in blood pressure control. And you should consume some specific minerals on a regular basis for good blood pressure management: calcium, magnesium, and potassium. But do most of us get enough of these? "If you're eating a healthy diet, you probably have nothing to worry about. But people eating a diet of processed and canned foods might need to be concerned, as well as people taking certain medications," says Dr. Randall Zusman, director of the Division of Hypertension at the Massachusetts General Hospital Heart Center.

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1/2 cup canned white
595 milligrams (mg)
of potassium, 67 mg of magnesium,
and 96 mg calcium.

3 ounces of cooked
490 mg of
potassium, and 91 mg of

1/2 cup cooked spinach:
419 mg potassium,
78 mg of magnesium, and
146 mg of calcium.

1 Potassium

Normal body levels of potassium are important for muscle function, including relaxing the walls of the blood vessels. This lowers blood pressure and protects against muscle cramping. Normal potassium levels also are important for the conduction of electrical signals in the nervous system and in the heart. This protects against an irregular heartbeat.

Potassium is found naturally in many foods, such as prunes, apricots, sweet potatoes, and lima beans. But food may not be enough to keep up your potassium levels if you take a diuretic for high blood pressure such as hydrochlorothiazide (Esidrix, HydroDiuril). These drugs cause potassium to leave your body in the urine, thereby lowering your body's potassium levels. "I'd say at least a third of patients on diuretics for heart failure or high blood pressure or edema don't get enough potassium from their diets. In those cases, we do use supplements," says Dr. Zusman. Don't try a supplement on your own. Too much potassium, like too little, can lead to dangerous irregular heart rhythms.

The Recommended Dietary Allowance (RDA) of potassium is 4.7 grams per day for both men and women ages 51 and older.

2 Magnesium

Magnesium helps regulate hundreds of body systems, including blood pressure, blood sugar, and muscle and nerve function. We need magnesium to help blood vessels relax, and for energy production, bone development, and transporting calcium and potassium. Just like potassium, too much magnesium can be lost in urine due to diuretic use, leading to low magnesium levels.

The National Institutes of Health (NIH) reports that most older adults in the U.S. don't get the proper amount of magnesium in their diets, although extreme magnesium deficiency is very rare. It's best to get the mineral from food, especially dark, leafy green vegetables, unrefined grains, and legumes. The RDA of magnesium is 420 milligrams (mg) per day for men ages 50 and older; 320 mg/day for women ages 50 and older.

Too much magnesium from a supplement or from magnesium-containing drugs such as laxatives may cause diarrhea. There are no known adverse affects of magnesium intake from food.

3 Calcium

Calcium is important for healthy blood pressure because it helps blood vessels tighten and relax when they need to. It's also crucial for healthy bones and the release of hormones and enzymes we need for most body functions. We consume it naturally in dairy products, fish with bones (such as canned salmon and sardines), and dark, leafy greens.

The RDA of calcium for men ages 51 and older is between 1,000 and 1,200 mg per day. For women ages 51 and older it's 1,200 mg per day. Unfortunately, most people get about 700 mg of calcium in their daily diet. So should you take a supplement to make up the difference?

That's tricky business. As we reported in June 2013, some evidence shows calcium supplements increase the risk of death from heart disease. "It's been controversial, so most of us advise our patients to get their calcium from food rather than from supplement pills," says Dr. Zusman. If it's not possible to get enough calcium from food, you can use a low-dose calcium supplement to reach your daily RDA.