Potassium

What it is

Potassium is a mineral and the most abundant positively charged ion inside the body's cells. It is an essential nutrient found in many foods and sold as a dietary supplement. Supplements use potassium chloride and several other salts such as citrate, gluconate and bicarbonate.

What the research says

Potassium is needed to keep fluid volume and electrical gradients across cell membranes. The strongest evidence concerns blood pressure. A 2013 meta-analysis rated as high quality the evidence that eating more potassium lowers blood pressure in people with hypertension. A 2006 Cochrane review of potassium supplement pills alone found no statistically significant effect and called that evidence not conclusive. Replacing ordinary salt with a potassium-containing salt substitute lowered stroke, cardiovascular events and death in a large trial in rural China. The main harm is high blood potassium (hyperkalaemia), mostly in people with kidney disease or taking medicines that hold on to potassium.

Evidence grade: Well established.

What goes wrong

Salt substitutes probably raise blood potassium slightly, and the trials excluded the people most at risk of harm, so safety in the general population is not settled. (Source 1)

• Systematic review, Moderate certainty.
• Size: 784 participants in 6 RCTs (blood potassium)
• Who: Adults; all 26 trials excluded people for whom extra potassium is known to be harmful.
• How long: 2 months to nearly 5 years.
• Result: Blood potassium MD 0.12 mmol/L (95% CI 0.07 to 0.18)
• Funding: Not stated in the abstract.

All 26 trials specifically excluded participants in whom an increased potassium intake is known to be potentially harmful.

A case report described repeated admissions with hyperkalaemia (serum potassium 6.7 to 7.2 mmol/L) in a patient with chronic kidney disease using a potassium salt substitute; the authors argue supplements and salt substitutes are under-recognised causes. (Source 2)

• Case report, Very low certainty.
• Size: 1 patient.
• Who: Adult with chronic kidney disease.
• How long: A few weeks of salt substitute use.
• Result: Salt substitute supplied 610 mg potassium per 1/4 teaspoon.
• Funding: Not stated.

Salt substitutes and dietary supplements are uncommon causes of hyperkalemia, but we propose that they are under-recognized and underdiagnosed causes in patients with chronic kidney disease.

US FDA position (as reported by NIH ODS, 2022): some oral potassium chloride products providing more than 99 mg are not considered safe because of small-bowel lesions. (Source 3)

• Official position, Certainty not rated.
• Size: Not applicable.
• Who: Not applicable.
• How long: Not applicable.
• Result: Not applicable.
• Funding: Government.

FDA has ruled that some oral drug products that contain potassium chloride and provide more than 99 mg potassium are not safe because they have been associated with small-bowel lesions.

Interaction (NIH ODS position, 2022): ACE inhibitors and angiotensin receptor blockers reduce potassium loss in urine and can lead to hyperkalaemia. (Source 3)

• Official position, Certainty not rated.
• Size: Not applicable.
• Who: People taking ACE inhibitors or ARBs.
• How long: Not applicable.
• Result: Not applicable.
• Funding: Government.

These medications reduce urinary potassium excretion, which can lead to hyperkalemia.

Interaction (NIH ODS position, 2022): potassium-sparing diuretics can cause hyperkalaemia, and monitoring is advised especially with impaired kidney function. (Source 3)

• Official position, Certainty not rated.
• Size: Not applicable.
• Who: People taking potassium-sparing diuretics.
• How long: Not applicable.
• Result: Not applicable.
• Funding: Government.

Experts recommend monitoring potassium status in people taking these medications, especially if they have impaired kidney function or other risk factors for hyperkalemia.

What the evidence supports

Higher potassium intake lowered blood pressure in adults with hypertension, but not in people without hypertension. (Source 4)

• Meta-analysis, High certainty.
• Size: 1,606 participants in 22 RCTs; 127,038 in 11 cohort studies.
• Who: Adults with and without hypertension.
• How long: RCTs of varying length.
• Result: Systolic -3.49 mm Hg (95% CI 1.82 to 5.15); diastolic -1.96 mm Hg (0.86 to 3.06)
• Funding: Not stated in the abstract (review done for WHO guideline work)

Increased potassium intake reduced systolic blood pressure by 3.49 (95% confidence interval 1.82 to 5.15) mm Hg and diastolic blood pressure by 1.96 (0.86 to 3.06) mm Hg in adults, an effect seen in people with hypertension but not in those without hypertension.

In cohort studies, higher potassium intake was associated with a lower risk of stroke. This is an association, not proof of cause. (Source 5)

• Meta-analysis, Moderate certainty.
• Size: 11 cohort studies, 127,038 participants.
• Who: Adults.
• How long: Cohort follow-up.
• Result: Stroke RR 0.76 (0.66 to 0.89); cardiovascular disease RR 0.88 (0.70 to 1.11) and coronary heart disease 0.96 (0.78 to 1.19) not significant.
• Funding: Not stated in the abstract.

Higher potassium intake was associated with a 24% lower risk of stroke (moderate quality evidence).

In a cluster-randomised trial in 600 Chinese villages, a salt substitute of 25% potassium chloride lowered rates of stroke, major cardiovascular events and death compared with regular salt. (Source 6)

• Randomized trial, Moderate certainty.
• Size: 20,995 participants.
• Who: Adults with previous stroke, or aged 60+ with high blood pressure, rural China.
• How long: Mean 4.74 years.
• Result: Stroke rate ratio 0.86 (95% CI 0.77 to 0.96; P = 0.006); death 0.88 (0.82 to 0.95)
• Funding: Independent (National Health and Medical Research Council of Australia); open-label.

The rate of stroke was lower with the salt substitute than with regular salt (29.14 events vs. 33.65 events per 1000 person-years; rate ratio, 0.86; 95% confidence interval [CI], 0.77 to 0.96; P = 0.006)

A Cochrane review found salt substitutes probably lower blood pressure slightly, with moderate-certainty evidence. (Source 1)

• Systematic review, Moderate certainty.
• Size: 21,414 participants in 20 RCTs (systolic)
• Who: Adults.
• How long: 2 months to nearly 5 years.
• Result: Systolic MD -4.76 mmHg (95% CI -6.01 to -3.50); diastolic MD -2.43 mmHg.
• Funding: Not stated in the abstract.

LSSS compared to regular salt probably reduce DBP on average (mean difference (MD) -2.43 mmHg, 95% confidence interval (CI) -3.50 to -1.36; 20,830 participants, 19 RCTs, moderate-certainty evidence)

What the evidence does not support

Potassium supplement pills alone did not produce a statistically significant drop in blood pressure in a Cochrane review, which called the evidence not conclusive. (Source 7)

• Systematic review, Low certainty.
• Size: 483 participants in 6 RCTs (425 in 5 pooled)
• Who: Adults with raised blood pressure.
• How long: 8 to 16 weeks.
• Result: Systolic mean difference -11.2 (95% CI -25.2 to 2.7); diastolic -5.0 (-12.5 to 2.4)
• Funding: Not stated in the abstract.

Potassium supplementation has no statistically significant effect on blood pressure.

The Cochrane authors said the supplement evidence was too small, short and inconsistent to be conclusive. (Source 7)

• Systematic review, Low certainty.
• Size: 2 high-quality trials, 138 participants.
• Who: Adults with raised blood pressure.
• How long: 8 to 16 weeks.
• Result: Systolic -7.1 (95% CI -19.9 to 5.7) in the two high-quality trials, not significant.
• Funding: Not stated in the abstract.

Due to small number of participants in the two high quality trials, the short duration of follow-up, and the unexplained heterogeneity between trials, the evidence about the effect of potassium supplementation on blood pressure is not conclusive.

Where the evidence is mixed

A dose-response meta-analysis found a U-shaped curve: the blood-pressure benefit weakened above about 30 mmol/day extra potassium and blood pressure rose above about 80 mmol/day, mainly in people already on blood-pressure drugs. (Source 8)

• Meta-analysis, Low certainty.
• Size: 32 RCTs.
• Who: Mostly adults with hypertension.
• How long: At least 4 weeks.
• Result: Weaker effect above 30 mmol/d difference; BP increase above about 80 mmol/d difference.
• Funding: Not stated in the abstract.

We observed a U-shaped relationship between 24-hour active and control arm differences in potassium excretion and BP levels, with weakening of the BP reduction effect above differences of 30 mmol/d and a BP increase above differences ≈80 mmol/d.

In the same trial, serious adverse events attributed to hyperkalaemia were not significantly more common with the salt substitute. (Source 6)

• Randomized trial, Moderate certainty.
• Size: 20,995 participants.
• Who: Adults at high cardiovascular risk, rural China.
• How long: Mean 4.74 years.
• Result: 3.35 vs 3.30 events per 1000 person-years; rate ratio 1.04 (0.80 to 1.37); P = 0.76.
• Funding: Independent (NHMRC Australia)

The rate of serious adverse events attributed to hyperkalemia was not significantly higher with the salt substitute than with regular salt

Where the research disagrees

Whether potassium supplements (as opposed to higher potassium intake overall) lower blood pressure

• Dickinson et al., Cochrane 2006, Systematic review of 6 RCTs, 483 participants: Potassium supplementation has no statistically significant effect on blood pressure. (Source 7)
• Aburto et al., BMJ 2013, Meta-analysis of 22 RCTs, 1,606 participants: High quality evidence shows that increased potassium intake reduces blood pressure in people with hypertension (Source 5)

How much

• Reference intake: NASEM (2019) set Adequate Intakes, not an RDA, based on the highest median intakes in US surveys: 3,400 mg/day for adult men and 2,600 mg/day for adult women (Table S-1). (Source 9)
• Upper limit: NASEM (2019) did not set a Tolerable Upper Intake Level, concluding there was insufficient evidence of toxicity risk in the apparently healthy population. (Source 9)
• Studied: Supplement trials gave 30 to 140 mmol/day of potassium. (Source 8)
• Studied: SSaSS used a salt substitute of 75% sodium chloride and 25% potassium chloride by mass in place of regular salt for a mean 4.74 years. (Source 6)

A common belief, and what the research shows

The belief: More potassium is always better for blood pressure.

What the research shows: A dose-response meta-analysis found a U-shaped pattern: 'Our findings indicate an adequate intake of potassium is desirable to achieve a lower BP level but suggest excessive potassium supplementation should be avoided, particularly in specific subgroups.'

Questions and answers

What is it?

Potassium is a mineral and an essential nutrient. It is the main positively charged ion inside cells. It occurs naturally in many foods and is sold as a supplement. (Source 3)

What does it do in the body?

Potassium keeps the right amount of fluid inside cells and maintains the electrical difference across cell membranes that nerves and muscles, including the heart, rely on. (Source 3)

Is it good or bad for you?

Good in the right amount. High-quality evidence shows that eating more potassium lowers blood pressure in people with hypertension. Too much can raise blood potassium dangerously, mainly in people with kidney disease or on certain medicines, and one meta-analysis found blood pressure began to rise again at very high supplement doses. (Source 5)

How do you get more of it?

Studies raised intake through food, supplement tablets (usually potassium chloride) and potassium-containing salt substitutes used in place of ordinary salt. Most US potassium supplements contain no more than 99 mg because of an FDA ruling on potassium chloride products. (Source 3)

If it is harmful, what reduces it?

Potassium is not harmful at normal intakes, but blood potassium can climb too high. Medicines that reduce potassium loss in urine, such as ACE inhibitors, ARBs and potassium-sparing diuretics, are a recognised cause, and kidney disease is the main risk factor. Treatment of high potassium is a medical matter. (Source 3)

Why might someone be low in it or missing it?

Low intake is common, since many people eat below the Adequate Intake. Loss through the gut or urine also lowers potassium: inflammatory bowel disease, laxative use, and loop or thiazide diuretics, which increase potassium loss in urine. (Source 3)

Which whole foods contain it or feed it?

Fruits and vegetables are the richest sources, along with legumes such as soybeans and potatoes. Meat, poultry, fish, milk, yogurt and nuts also contain potassium. (Source 3)

What happens if you do not have it?

Mildly low blood potassium causes constipation, tiredness and muscle weakness. Severely low levels (below about 2.5 mmol/L) can cause muscle paralysis, poor breathing and abnormal heart rhythms. (Source 3)

How can you test for it?

A standard blood (serum) potassium test is widely available and detects low or high blood levels. It does not reliably show how much potassium is stored in body tissues. (Source 3)

References

1. Cochrane Database of Systematic Reviews. Replacing salt with low-sodium salt substitutes (LSSS) for cardiovascular health in adults, children and pregnant women. 2022. PMID 35944931, DOI 10.1002/14651858.CD015207. Read the source
2. Cureus. Hyperkalemia from Dietary Supplements. 2016. DOI 10.7759/cureus.859. Read the source
3. NIH Office of Dietary Supplements. Potassium - Health Professional Fact Sheet (updated June 2, 2022). 2022. Read the source
4. BMJ. Effect of increased potassium intake on cardiovascular risk factors and disease: systematic review and meta-analyses (abstract Results section). 2013. PMID 23558164, DOI 10.1136/bmj.f1378. Read the source
5. BMJ. Effect of increased potassium intake on cardiovascular risk factors and disease: systematic review and meta-analyses (abstract Conclusions section). 2013. PMID 23558164, DOI 10.1136/bmj.f1378. Read the source
6. New England Journal of Medicine. Effect of Salt Substitution on Cardiovascular Events and Death. 2021. PMID 34459569, DOI 10.1056/NEJMoa2105675. Read the source
7. Cochrane Database of Systematic Reviews. Potassium supplementation for the management of primary hypertension in adults. 2006. PMID 16856053, DOI 10.1002/14651858.CD004641.pub2. Read the source
8. Journal of the American Heart Association. Potassium Intake and Blood Pressure: A Dose-Response Meta-Analysis of Randomized Controlled Trials. 2020. PMID 32500831, DOI 10.1161/JAHA.119.015719. Read the source
9. National Academies of Sciences, Engineering, and Medicine. Dietary Reference Intakes for Sodium and Potassium (Summary). 2019. DOI 10.17226/25353. Read the source