Q: You have often written about the benefits of potassium, yet you advise against potassium supplements. Why?
A: While there’s no doubt that a diet rich in potassium provides cardiovascular benefits (notably for blood pressure control and stroke prevention), that may not be true of supplements—which can actually be dangerous for many people.
High-potassium foods—vegetables and fruits, along with beans, dairy products, fish, and nuts—contain many nutrients and other compounds that help account for the health benefits. So it’s hard to say how much the benefits come from the potassium itself. In large part, the mineral may simply be a marker for a healthy diet. That may be why studies testing the effect of potassium supplements on blood pressure, for instance, have had inconsistent or unclear results.
Blood levels of potassium are tightly regulated by the body, mostly by the kidneys. But when the kidneys aren’t working properly, potassium can rise to high levels and cause dangerous heart rhythm problems and even cardiac arrest.
Thus, people who have impaired kidney function (which includes lots of older people, many of whom are unaware of it) as well as those with diabetes, heart failure, or certain other conditions should avoid supplemental potassium and salt substitutes that contain potassium. The same goes for anyone taking anti-hypertension drugs that can increase potassium retention (such as ACE inhibitors and potassium-sparing diuretics) and even NSAID pain relievers (such as aspirin, ibuprofen, and naproxen).
High-dose potassium supplements and high-potassium salt substitutes pose the greatest risk for these groups. Most supplement makers limit potassium to less than 100 milligrams per capsule because of a longstanding FDA rule requiring a label warning at higher doses. Extended-release potassium tablets (600 or 750 milligrams), available only by prescription, are given primarily to people who take medication that depletes potassium from the body, such as certain diuretics.
There is no RDA for potassium, only an Adequate Intake, which the National Academy of Sciences recently lowered from 4,700 milligrams a day to 3,400 for men and 2,600 for women.
Bottom line: Many Americans consume too little potassium, but they should get it from foods, not pills, unless their doctors have prescribed the supplements. Among the best sources of potassium are potatoes, spinach, salmon, bananas, milk, orange juice, broccoli, lentils, beans, and dried fruit.