Introduction
Potassium is a mineral that plays numerous important functions in the body. It is present in high amounts in most fruits, and also found in vegetables, legumes, and dairy products. While humans evolved on a diet very high in potassium and low in sodium, the modern diet is high and sodium and low in potassium. Thus, the human body effectively retains sodium and readily excretes potassium, and the combination of this with the modern diet can result in sodium overload and potassium depletion [1]. In turn, this may be an important contributor to the high incidence of high blood pressure and cardiovascular disease in modern times. This article will discuss some of the research on the role dietary potassium plays in the development of high blood pressure and cardiovascular disease.
Blood pressure
A large amount of research has been done on the relationship between potassium intake and blood pressure. Research on this relationship has been difficult for numerous reasons, including interindividual variation, difficulty in measuring electrolyte intake, the fact that sodium and potassium intake tend to change simultaneously, and the fact that self-report data is often biased. However, there is now considerable evidence that both increasing potassium and decreasing sodium intake is beneficial for blood pressure control, although the effect of sodium has been more consistently observed [2].
Epidemiological and cross-cultural studies indicate that populations and individuals consuming greater amounts of potassium haver lower blood pressure [3-4]. Many large trials have also been conducted, and some, but not all, indicate that supplementation with potassium reduces blood pressure in those with both high and normal blood pressure [4-5]. A meta-analysis of 33 trials found that potassium supplementation caused an average decrease in systolic and diastolic blood pressure of 3.1 and 2.0 mmHg respectively. Many clinical trials also suggest that this effect is greater among those with low dietary intake of potassium [4]. One large-scale trial indicated that increasing dietary potassium causes a blood pressure reduction similar to that of most blood pressure medications [1].
There are multiple reasons why potassium decreases blood pressure. First, potassium facilitates sodium excretion. Potassium may also directly cause vasodilation. Potassium also reduces cardiac sensitivity to catecholamins and angiotensin II and suppresses sodium-induced increases in catecholamines [1, 6]. Increasing potassium intake, even in the presence of high sodium intake, has an effect similar to that of reducing sodium intake [3]. The benefits of reducing dietary sodium and increasing potassium may be additive, as the dietary ratio seems to be more important than the total dietary content of either [1].
The response to potassium supplementation varies from individual to individual. One study on eight healthy subjects found that in two of them the sodium/potassium ratio was correlated with blood pressure whereas no effect was seen in the other eight [7], while a larger study found that 47% of normotensive adults were sensitive to dietary sodium and potassium [3]. Factors that play a role in individual variation include genetics, gender, body size, and age [2].
Stroke
Another related benefit of high amounts of dietary potassium is decreased stroke risk. Epidemiologically, diets high in potassium are associated with up to a 40% reduction in the incidence of stroke, but this is when other dietary factors are not controlled for [1]. However, several studies that controlled for other dietary factors found that increased amounts of dietary potassium are associated with a significant reduction in stroke risk, including a 12-year study on over 800 subjects [8]. This reduction in stroke risk occurs in those with both high and normal blood pressure, and is greater in men [9].
Recommendations & Precautions
The best way to increase potassium intake is to consume foods that are high in potassium. A low dose potassium supplement (100-500 mg) is also not a bad idea, although high amounts of potassium supplements should not be taken without medical supervision. Blood levels of potassium are tightly regulated, and highly bioavailable potassium supplements may increase blood levels significantly, leading to the possibility of acute toxicity. Using a protein powder or MRP with high potassium content is an easy way to increase the amount of potassium in the diet.
References:
1. J Am Coll Cardiol. 2004 Jan 21;43(2):155-61. What is the optimal serum potassium level in cardiovascular patients? Macdonald JE, Struthers AD.
2. Ann Epidemiol. 2002 Nov;12(8):587-95. Electrolyte intake and nonpharmacologic blood pressure control. Espeland MA, Kumanyika S, Yunis C, Zheng B, Brown WM, Jackson S, Wilson AC, Bahnson J.
3. Health Psychol. 1999 May;18(3):229-40. Potassium supplementation induces beneficial cardiovascular changes during rest and stress in salt sensitive individuals. West SG, Light KC, Hinderliter AL, Stanwyck CL, Bragdon EE, Brownley KA.
4. J Hypertens. 2001 Jul;19(7):1325-31. Effect of potassium supplementation on blood pressure in Chinese: a randomized, placebo-controlled trial. Gu D, He J, Wu X, Duan X, Whelton PK.
5. Am J Hypertens. 2002 Feb;15(2 Pt 1):130-6. Serum potassium is not associated with blood pressure tracking in the Framingham Heart Study. Walsh CR, Larson MG, Vasan RS, Levy D.
6. Hypertension. 1999 Aug;34(2):181-6. Effects of potassium on blood pressure in salt-sensitive and salt-resistant black adolescents. Wilson DK, Sica DA, Miller SB.
7. Clin Exp Hypertens. 1999 Oct;21(7):1189-202. Daily response of blood pressure to day-to-day variation of urinary sodium to potassium ratio. Yoshida M, Koyama H, Moji K, Aoyagi K, Takemoto T, Suzuki S, Satoh H.
8. Neurology. 2002 Aug 13;59(3):314-20. Serum potassium level and dietary potassium intake as risk factors for stroke. Green DM, Ropper AH, Kronmal RA, Psaty BM, Burke GL; Cardiovascular Health Study.
9. Am J Hypertens. 2003 Oct;16(10):806-13. Serum potassium and stroke risk among treated hypertensive adults. Smith NL, Lemaitre RN, Heckbert SR, Kaplan RC, Tirschwell DL, Longstreth WT, Psaty BM.
