Potassium Supplements Review
Initial Posting: 11/15/16 Updated: 6/20/20
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- Do I need it? Potassium is essential for the proper functioning of the nervous system, skeletal system, heart, and metabolism, as well as maintaining normal blood pressure (See What It Is). It can easily be obtained through the diet, but people taking certain drugs or with conditions affecting the kidneys or gut may be deficient (See What to Consider When Using). Low potassium is also common among people hospitalized with COVID-19, caused by the new coronavirus.
- What does it do? Potassium supplements are typically used only to treat or prevent potassium deficiency. Supplementing with potassium may also help to reduce high blood pressure and the risk of kidney stones (See What It Does).
- How much to take? For preventing potassium loss, potassium is often recommended at doses of 200 to 400 mg, taken 3 to 4 times daily (for a total daily dose ranging from 600 mg to 1,600 mg). For lowering blood pressure in people with hypertension, larger amounts are often used (3,000 mg per day) (See What to Consider When Using). Nearly all common forms of potassium are absorbed equally well (See What to Consider When Buying).
- Best Choice? CL's tests found most potassium supplements to be of high quality, but arsenic contamination was found in one product (See What CL Found). Among the products which passed testing and were Approved for quality, ConsumerLab.com identified several which represented its Top Picks.
- Cautions: Potassium from supplements may cause diarrhea, nausea, stomach pain, mild gas and vomiting, which may be reduced by taking with meals. Less common side effects include confusion, irregular heartbeat and shortness of breath. People with kidney disease and people taking potassium-sparing diuretics, ACE inhibitors, or trimethoprim/sulfamethoxazole should not take potassium supplements without medical supervision (See Concerns and Cautions).
What It Is:
Potassium is an essential mineral. It is found in foods and supplements in many forms, including potassium bicarbonate, potassium citrate, potassium gluconate, potassium acetate and (particularly in some salt substitutes) as potassium chloride (See ConsumerTips: What to Consider when Buying for more information about forms of potassium). Potassium is also used in supplements to stabilize other key compounds, such as in potassium iodide supplements where potassium stabilizes iodine as a radioprotective agent (see separate review of Radioprotective Agents).
What It Does:
Potassium, like sodium and chloride, is an important electrolyte involved in the proper functioning of the nervous system, skeletal system, cardiac muscle, and metabolism, as well as maintaining normal blood pressure.
Although most people get enough potassium from their diets, some research has noted a decline in potassium levels in people in the U.S. An analysis of over 50,000 men, women and children (ages 12 - 80) from 1999 to 2016 found that average annual blood levels of potassium decreased (from 4.14 mmol/L to 3.97 mmol/L) and the prevalence of potassium deficiency increased by 7.3% and was more common in non-Hispanic black than non-Hispanic white individuals. The researchers suggested that a decline of potassium in crop soil and fertilizer, as well as increased consumption of processed foods and decreased consumption of fruits and vegetables may play in these trends (Sun, J Am Coll Nutr 2020).
Normal blood levels of potassium range between 3.6 and 5.0 mmol/L (NIH Fact Sheet 2020).
Potassium supplements are typically used only to treat or prevent potassium deficiency (hypokalemia) caused by excessive potassium loss. Potassium deficiency can result from the use of diuretic drugs ("water pills") to treat high blood pressure and can also occur in cases of prolonged vomiting, diarrhea or laxative abuse. Deficiency can cause muscle weakness, irregular heartbeat, listlessness, mood changes, irrational behavior, nausea, and vomiting. Some research indicates that potassium may help reduce hypertension -- particularly in African-Americans and people who consume too much sodium.
Potassium deficiency may also cause muscle spasms, but there are no published, double-blind clinical studies on the effects of potassium supplementation on muscle cramps. Furthermore, nighttime muscle cramps and exercise-related muscle cramps do not appear to be related to potassium levels (Allen, Am Fam Physician 2012). A small study in India among people with moderate to severe restless leg syndrome suggested a benefit from taking a daily dose of 391 mg of potassium (as 1,080 mg of potassium citrate): After one month, the majority of people reported having no symptoms (Rauf, Pharm Pharmacol Int J 2016). However, this study did not include a control group, so it's not possible to draw conclusions from it.
Kidney stone disease
Taking certain forms of potassium may reduce the risk of kidney stones.
A clinical study found that patients who took 6,480 mg (or 60 milliequivalents [mEq]) of potassium citrate daily (divided into three equal doses, each taken after a meal) had no stone recurrence after one year, compared to a 28.5% stone recurrence rate in patients who did not take potassium citrate (Soygur, J Endourol 2002).
Several products reviewed by ConsumerLab.com (below) provide potassium citrate, although the suggested serving sizes are much lower than those used to prevent kidney stones: Most potassium gluconate supplements typically provide 99 mg of potassium from 258 mg (2.4 mEq) of potassium citrate, so you would need to take many times the suggested daily serving to achieve therapeutic levels of citrate. It is important to understand that it is not the potassium which is helpful but the citrate portion of the molecule, as it is the citrate which interferes with calcium stone formation. Foods and beverages rich in citrate, such as citrus and melon, are, for this reason, often recommended for people with kidney stone disease.
Another clinical study found that 2 tablets containing 1,954 mg of a patented potassium complex taken 3 times daily (providing a daily total of 1,638 mg potassium, 252 mg magnesium and 3,971 mg citrate) for up to 3 years reduced the risk of kidney stone recurrence by 85% in people with active kidney stone disease compared to placebo (Ettinger, J Urol 1997). ConsumerLab.com has not been able to identify any supplements on the market that contain this patented form of potassium-magnesium-citrate. Therefore, the best way to get the amounts used in this study would be to purchase potassium citrate and magnesium citrate supplements separately. However, be aware that potassium citrate and magnesium citrate can interfere with certain drugs or have other side-effects (see the Concerns and Cautions section of this Review and the Magnesium Review) so it's best to consult your healthcare provider if you are considering taking them at these doses.
Potassium phosphate may also help people with kidney stone disease because the phosphate decreases excessive calcium in the urine in people with hypercalciuria, the most common cause of calcium kidney stones. A small clinical study found 2,496 mg of potassium (as potassium phosphate) taken as four tablets twice daily for four years reduced urinary calcium by 30 to 35% in patients with absorptive hypercalciuria (Heller, J Urol 1998). [Note: In studies, doses of potassium are usually listed in units of "milliequivalents" (mEq), but we have converted these to milligrams (mg), the unit used on most supplement labels.]
Potassium will not prevent COVID-19, the infection caused by the SARS-CoV-2 coronavirus, but low potassium levels have been noted in people hospitalized with COVID-19. Doctors in China reported that among a group of 175 patients hospitalized with COVID-19, 69 (39%) had hypokalemia (low potassium in the blood) and another 39 (22%) had severe hypokalemia. Supplementing with about 3 grams of potassium daily helped correct these deficiencies in most patients. The presence of underlying disease, particularly hypertension, was associated with the severity of hypokalemia. On the other hand, there was no association between hypokalemia and common upper respiratory symptoms, such as cough and runny nose (i.e., if those are your only symptoms, you probably don't have to worry about your potassium level.) (Chen, preprint in medRxiv 2020 -- Not yet peer-reviewed). A study of 290 hospitalized patients with confirmed COVID-19 in Italy found that although hypokalemia was common, it tended to be mild and was treatable with oral potassium supplements. It was not associated with poor outcomes or mortality (Alfano, preprint in medRxiv 2020 -- Not yet peer-reviewed).
The apparent reason for hypokalemia in COVID-19 is that the point of entry into cells for the coronavirus SARS-CoV-2 is an enzyme on cell surfaces called angiotensin I converting enzyme 2 (ACE2). ACE2 is found on many types of cells, including those in the lungs, intestines, kidneys, and heart. It normally helps regulate blood pressure through effects on sodium and potassium. The virus inactivates ACE2, leading to excretion of potassium. This explanation was further supported by the finding of excess potassium in the urine of patients with hypokalemia, indicating that the potassium loss is mainly through the kidneys (from potassium it normally filters from the blood) as opposed to diarrhea -- which is also common in COVID-19.
There are hypothetical concerns that taking prescription ACE-inhibitors and angiotensin receptor-blockers (ARBs) may increase ACE2 on cell surfaces, potentially increasing the risk of developing severe COVID-19 (Fang, Lancet 2020; Diaz, J Trav Med 2020) but there are also cautions not to stop taking such medications as they not only control high blood pressure but may helpful in treating COVID-19 (Danser, Hypertension 2020; de Simone, Eur Soc Cardio 2020).
See the Encyclopedia for more information about clinical studies on Potassium.
Quality Concerns and What CL Tested For:
Neither the FDA nor any other federal or state agency routinely tests supplements for quality prior to sale. Consequently, ConsumerLab.com tested potassium products to determine if they contained listed amounts of potassium. Products containing whole herb and/or 250 mg or more of minerals per daily serving were tested for contamination with lead, cadmium and arsenic, as these can occur in plant-based supplements. Standard tablets and caplets were also tested to be sure that they would disintegrate ("break apart") properly (see Testing Methods and Passing Score).