Potassium is a mineral found naturally in many foods. It is needed in the body for the normal functioning of the heart, nerves and muscles. High potassium levels can lead to dangerous heart rhythms. Low potassium levels can cause muscle weakness and problems with the heart rhythm too. Long-term low levels of potassium has been linked to high blood pressure, heart disease, and stroke. Low potassium is particularly likely to raise your blood pressure if you have a high intake of salt (sodium chloride).
Potassium relaxes the walls of the blood vessels, lowering blood pressure. It also protects against muscle cramping.
What are normal levels of potassium?
What can cause low potassium levels?
Having low levels of potassium in the blood is known as hypokalaemia. It can be caused by the following risk factors:
- If you lose a lot of fluid in diarrhoea and through being sick (vomiting).
- With excessive sweating - for example, in very hot countries.
- If you have anorexia nervosa (this is due to a combination of being sick and taking too many laxatives, resulting in loss of fluids).
- After eating too much liquorice, or if high doses of liquorice-containing herbal medicines are taken.
- As a side-effect of medication, especially 'water' tablets (diuretics). This is the most common cause of low potassium.
A diuretic is a medicine which increases the amount of urine you pass out from your kidneys. There are different types of diuretic tablets and some, particularly loop diuretics and thiazide diuretics, can cause too much potassium to be lost with the extra urine passing out of the body. This can make the potassium levels very low, which can be quite dangerous. Potassium-sparing diuretics can prevent this from happening.
What are the symptoms of low potassium?
Low levels of potassium can make you feel tired and sick (nauseous) and can cause high blood pressure. Very low levels can result in muscle weakness, swelling (oedema) and dangerous heart rhythms.
What can cause high potassium levels?
High potassium in the blood is known as hyperkalaemia. It can be caused by the following risk factors:
- Sudden kidney injury or severe chronic kidney disease, due to the inability of the kidneys to remove potassium from the body.
- Some medications - most commonly angiotensin-converting enzyme (ACE) inhibitors.
If you need to follow a low-potassium diet because of kidney problems (such as kidney stones), you should be referred to a specialist dietician who will be able to advise you.
But for most people, eating potassium-rich foods is important to maintain a healthy diet. A reasonably high potassium intake helps to reduce blood pressure, which in turn reduces the risk of strokes and heart attacks.
How much potassium do you need per day?
The World Health Organization recommends that adults should eat at least 3510 mg of potassium daily. However, studies looking at potassium intake and stroke risk have found that very few people meet that target.
Which foods are high in potassium?
Potassium is present in many different foods, particularly in fruit and vegetables. Therefore, making sure that you have at least five portions of fruit and vegetables daily is very important.
Processed foods tend to contain lower levels of potassium. For example, wholemeal bread and brown rice have higher levels or potassium than their white equivalents.
Salt substitutes, such as potassium chloride, are made from potassium, and using these instead of salt will increase your potassium intake. However, it is probably healthier to get used to food tasting less salty than to replace salt with this alternative.
Some vegetables which contain high levels of potassium are:
- Medium baked potato (skin on) 925 mg.
- Medium baked sweet potato (skin on) 450 mg.
- Medium raw tomato 290 mg.
- Half an avocado 490 mg.
Dark green leafy vegetables are also rich in potassium.
Fruits which contain high levels of potassium include:
- Medium banana 425 mg.
- ¼ cup of raisins 270 mg.
- Small orange 240 mg.
- Medium pear 200 mg.
Other tropical fruits that are also rich in potassium include mango, papaya, kiwi and melon.
Protein foods which contain high levels of potassium include:
- Salmon (80 g portion) 534 mg.
- ½ cup of lentils 365 mg.
- Turkey (80 g portion) 250 mg.
- 2 tablespoons of peanut butter 210 mg.
Other pulses and beans are also good sources of potassium.
Dairy foods rich in potassium:
- Small pot of yoghurt 350 mg.
- 1 cup of milk 360 mg.
These are just examples of potassium-rich foods but most fresh foods contain quite high levels of potassium. So a normal healthy diet containing a variety of fruit and vegetables will provide enough potassium for most people. However, you should seek medical advice if you are experiencing severe symptoms from high or low potassium intake.
Further reading and references
Guideline: sodium intake for adults and children; World Health Organization (December 2012)
Guideline: potassium intake for adults and children; World Health Organization (December 2012)
Vinceti M, Filippini T, Crippa A, et al; Meta-Analysis of Potassium Intake and the Risk of Stroke. J Am Heart Assoc. 2016 Oct 65(10). pii: JAHA.116.004210. doi: 10.1161/JAHA.116.004210.
Newberry SJ, Chung M, Anderson CAM, Chen C, Fu Z, Tang A, Zhao N, Booth M, Marks J, Hollands S, Motala A, Larkin J, Shanman R, Hempel S; Sodium and Potassium Intake: Effects on Chronic Disease Outcomes and Risks [Internet]. Rockville (MD): Agency for Healthcare Research and Quality (US) 2018 Jun. Report No.: 18-EHC009-EF.
National Academies of Sciences, Engineering, and Medicine; Health and Medicine Division Food and Nutrition Board