Potassium: bones, stones, & strokes on the line.

Potassium is the seventh most plentiful mineral on earth, but it's much too scarce in Americans' diets. More potassium, say experts, would help protect us against high blood pressure, strokes, kidney stones, and bone loss.

"In general, the higher the potassium in our diets, the better," says Lawrence Appel, who chaired a panel of the National Academy of Sciences (NAS) that issued a report on potassium last February. (1) U.S. women consume about 2,500 milligrams a day, while men consume about 3,000 mg. That's not enough.

"Most men and women age 14 and up should be getting at least 4,700 mg of potassium each day from food ... and fruits and vegetables are a particularly rich source," said Appel in announcing the panel's conclusions. "That means people will have to increase their consumption of fruits and vegetables to 10 servings a day to get enough potassium." Appel is a hypertension expert and professor of medicine at Johns Hopkins University in Baltimore.

Manufacturers of processed food were quick to howl. A target of 4,700 mg a day is "unrealistically high," said Robert Earl, senior director of nutrition policy for the National Food Processors Association.

And for people who eat a diet filled with junk foods, he's probably right. Foods like white bread, doughnuts, and soft drinks have less potassium than unprocessed foods.

A Critical Mineral

Our bodies spend 20 to 40 percent of the total energy necessary to keep us alive continually pumping potassium into--and sodium out of--cells. Without potassium, nerve impulses wouldn't travel and muscles wouldn't contract. And that's just the start.

"Research over the past decade clearly documents that potassium can lower blood pressure and possibly the risk of stroke," says Johns Hopkins's Appel. "Increased potassium also lowers the risk of kidney stones and might prevent bone loss."

* Blood pressure. In 31 good studies, researchers gave an average of 3,100 mg a day of potassium to people with and without hypertension for four days to six months. Blood pressure dropped an average of 3 points (systolic) over 2 points (diastolic) compared to people who took a placebo. (2)

And the more sodium the participants were consuming, the more their blood pressure fell. "An increased intake of potassium tends to help mute the effects of sodium in the diet," explains Paul Whelton, senior vice president of academic affairs at Tulane University and a member of the NAS potassium panel. That's because potassium makes the kidneys excrete more sodium.

"If you have high blood pressure, just consuming more potassium won't be enough to control it," cautions Ralph Sacco of the Neurological Institute of Columbia University College of Physicians and Surgeons in New York. "But every little bit helps."

* Stroke. "If everybody in the country increased their potassium intake to reduce their blood pressure by a few points, that would have a big impact on the number of strokes," says Sacco, who is also director of the Stroke Division at New York Presbyterian Hospital.

Among 43,000 men in the Health Professionals Study, those who consumed the most potassium (about 4,300 mg a day) over an eight-year period had a 40 percent lower risk of strokes--from clots or bleeding--than those who consumed the least (about 2,400 mg a day). (3)

And among 859 middle-aged and older men and women in the Rancho Bernardo Study in California, those who consumed the most potassium over 12 years were less likely to die of a stroke than those who consumed the least. (4) In other studies, potassium had a weaker effect on the risk of stroke. (5)

"It would be nice to have randomized trials comparing the effect of potassium with a placebo on the risk of stroke," says Sacco. "But that's not available right now."

"How potassium prevents strokes isn't entirely clear," he adds, "but it may work through its effect on blood pressure." High blood pressure can damage arteries, especially small ones, "and small-artery disease is one of the big causes of strokes."

* Kidney stones. "Potassium citrate, the kind that occurs naturally in foods, can help protect against kidney stones," says Khashayar Sakhaee of the University of Texas Southwestern Medical Center at Dallas.

That was clear in three studies that followed 164,000 men and women in the United States and Finland for four to 12 years. Those who consumed the most potassium from food (at least 4,000 mg a day) had a 25 to 50 percent lower risk of kidney stones than those who consumed the least (generally less than 3,000 mg a day). (6-8)

Researchers have also given potassium citrate to people who keep getting kidney stones.

In one study, 18 men and women who got 3,600 mg to 4,700 mg of potassium a day from food and supplements went from an average of 20 stones per year for the whole group to just two stones per year. (9) There were no fewer stones in the 20 people who took a placebo.

To figure out how the mineral may prevent kidney stones, Sakhaee and his colleagues gave 1,560 mg of potassium a day (from potassium citrate supplements) to 18 stone-free post menopausal women. (10)

In just two weeks, "the amount of calcium in their urine dropped, there was more citrate in their urine to bind up calcium, and their urine became less acidic," explains Sakhaee.

"All of these changes make stones less likely to form."

* Bone loss. "Potassium citrate may be able to slow bone loss," says Sakhaee. "The citrate is metabolized into bicarbonate to neutralize acid in the body."

If there's not enough bicarbonate available, the body takes calcium carbonate from the bones to balance the acid excess. "And that can lead to bone loss," he adds.

In Sakhaee's potassium citrate study, the 18 women who were getting 1,560 mg a day of potassium "cut their daily loss of calcium in the urine by 50 mg in just two weeks, compared to when they received a placebo," says the researcher. (10) "And there was a significant decline in the signs of bone turnover."

Another study found similar results in young men and women in just seven days. (11)

Too Much?

Can healthy people get too much potassium from food? No. But those who have trouble excreting excess potassium could consume too much.

"People with kidney disease and advanced diabetes shouldn't increase their potassium intake until they have spoken with their doctor," says Johns Hopkins's Laurence Appel. Ditto for those who take certain drugs to lower their blood pressure, he adds.

Potassium supplements, on the other hand, can be toxic even to healthy people. (A dangerous irregular heartbeat is the most serious side effect.) Other than what's in your multivitamin-and-mineral, don't take a potassium supplement without your doctor's approval.

Piling Up the Potassium

Fruits and vegetables are the best sources, especially of potassium citrate, which may prevent kidney stones and bone loss.

Potassium chloride, which is used in salt substitutes and some supplements, can lower blood pressure and the risk of stroke, but "it doesn't prevent the loss of calcium in urine or do the other things that help prevent kidney stones and bone loss," says researcher Khashayar Sakhaee.

Food                                      Potassium
(1/2 cup cooked vegetable, fruits raw)         (mg)

Potato (1)                                      940
Sweet Potato (1)                                540
Banana (1)                                      490
Halibut (3 oz. cooked)                          490
Lima beans                                      490
Fresh tuna (3 oz. cooked)                       480
Swiss chard                                     480
Acorn squash                                    450
Spinach                                         420
Salmon (3 oz. cooked)                           390
Cantaloupe (1/4 melon)                          370
Lentils                                         370
Milk (1 cup)                                    370
Watermelon (2 cups)                             320
Grapes (1 cup)                                  310
Pork (3 oz. cooked)                             310
Raisins (1/4 cup)                               310
Pistachios (50)                                 300
Flounder (3 oz. cooked)                         290
Parsnits                                        290
Pinto beans, canned                             290
Beef (3 oz. cooked)                             270
Wheat germ (2 Tbs.)                             270
Brussels sprouts                                250
Prunes (4)                                      250
Orange (1)                                      230
Zucchini                                        230
Artichokes                                      220
Almonds (20)                                    210
Chickpeas, canned                               210
Collard greens                                  210
Chicken (3 oz. cooked)                          200
Tuna, canned (3 oz.)                            200
Peanuts (30)                                    190

(1) Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. The National Academies Press, Washington, D.C. 2004.

(2) J. Amer. Med. Assoc. 277:1624, 1997

(3) Circulation 98: 1198, 1998.

(4) New Eng. J. Med. 316: 235, 1987.

(5) Stroke 30:1772, 1999.

(6) New Eng. J. Med. 328: 833, 1993.

(7) Ann. Intern. Med. 126: 497, 1997.

(8) Amer. J. Epidemiol. 150: 187, 1999.

(9) Journal of Urology 150:1761, 1993.

(10) Journal of Urology 172: 958, 2004.

(11) Amer. J. Physiol. Renal Physiol. 284: F32, 2003.