Potassium: Your Heart and Vasculature Will Love it! Meta-Analyses Show: Supplements Work, but Ain't Necessary

Foods, not supplements should be your go-to potassium source.

You've read about the importance of adequate potassium intakes and the lack of potassium (esp. in relation to sodium, where only 10% of the US adults meet the Na:K ratio the WHO recommends to reduce your overall mortality risk) in our diets at the SuppVersity, before (read more about potassium deficits). You've also learned that potassium supplements can be necessary during very low-calorie diets where they prevent the paradoxical induction of insulin resistance (read more about potassium and insulin resistance).

What you haven't read yet, however, is the number Tang et al. put on the effect of supplemental potassium on vascular function in their recent review and meta-analysis in the International Journal of Cardiology (Tang. 2016).
The scientists conducted a literature search on the PubMed database and included all articles that were published before April, 2016. As indices of vascular function, the researchers selected...

• the pulse wave velocity (PWV), which has a strong correlation with cardiovascular events and all-cause mortality (7.9x increased CVD death risk in Blacher et al. 1999a; 5.4x increased all-cause mortality risk in Blacher et al. 1999b; see also Cruickshank, 2002 and Laurent, 2001)
• the augmentation index (AI), which is a sensitive marker of arterial status and predictor of adverse cardiovascular events in a variety of patient populations, where a higher augmentation index is associated with target organ damage (Shimizu. 2008), 
• the pulse pressure (PP), which is the difference between the systolic and diastolic pressure readings and has been found to be associated w/ a significantly increased risk of cardiovascular disease and CV mortality (e.g. +20% with every 10 mm Hg increase in pulse pressure in Blacher et al. 2000),
• the flow mediated dilatation (FMD), of which a recent meta-analysis of Matsuzawa et al. (2015) shows that each meager 1% increase in FMD translates in a 12% reduction in predicted cardiovascular events,
• the glycerol trinitrate responses (GTN), which can tell you how effectively your arteries can relax when that's indicated, and
• the level of intercellular cell adhesion molecule-1 (ICAM-1), which is a soluble adhesion molecule and prediction of coronary heart disease that is associated with increased CHD risk (e.g. +68% in Malik et al. 2001 comparing the highest to lowest tertiles)

Data from all seven randomized controlled studies (409 patients in total) were pooled as standardized mean difference (SMD) with 95% confidence intervals. The dosage of potassium that was used in the studies ranged from 40 to 150 mmol/day (1.6-6g/day). The duration of the interventions was between 6 days and 12 months.

Figure 1: Forest plots of studies testing the effects of potassium supplementation on arterial stiffness: A. Pulse wave velocity (PWV); B. Augmentation index (AI); and C. Pulse pressure (PP). The results revealed a significant improvement in PP (p=0.010), but no improvement in PWV (p=0.391) and AI (p=0.184 | typos corrected in figure from Tang. 2016)

The results of the meta-analysis show benefits for all parameters of arterial stiffness, but a statistically significant effect only for one, but an important parameter: the pulse pressure (PP; Figure 1.C). From previous meta-analyses, we know that the overall effect on people's heart rate is only modest (potassium doses of 0.9–4.7 g/d for 2–24 weeks changed heart rate by 0.2 bpm according to Gijbers et al. 2016).

Figure 2: Forest plots of studies testing the effects of potassium supplementation on blood pressure: A. Systolic blood pressure (SBP); and B. Diastolic blood pressure (DBP). The results indicated a significant improvement in SBP (p=0.044), but no improvement in DBP (p=0.122 | typos corrected in figure from Tang. 2016

The effects on the subjects' systolic blood pressure which was also assessed by Tang et al. (2016), on the other hand, is quite significant (see Figure 2) and a logical mechanistic consequence of the improved vascular elasticity. Benefits for ICAM-1 and FMD exist, but don't reach statistical significance due to significant inter-study differences (data not shown).

Overall, the experimental evidence in favor of potassium supplementation is scarce and the "wide variation of evidences make it difficult to make a definitive conclusion" (Tang. 2016). 

That's in contrast to the epidemiological evidence, by the way. The latter, which describes the effect of high and low dietary potassium intake clearly indicates that high(er) potassium intakes are associated with a reduced risk of stroke (-24% | Aburto. 2013; 20% | D'Elia. 2014), and curvilinearly associated reduced risk of incident cardiovascular and all-cause mortality (e.g. O'Donnell. 2014 | see Figure 3).

Figure 3: Curvilinear association between urinary potassium, a good marker of your potassium balance with higher values being indicative of high intakes, and (A) risk of cardiovascular and (B) all-cause mortality (O'Donell. 2014).

I guess I could keep enumerating studies, here, but in conjunction with previous articles about the beneficial effects of potassium you should have learned enough about this deficiency mineral to be incentivized to double-check your dietary intake and resort to potasium citrate or bicarbonate (check out what potassium bicarbonate may be able to do for your gains | "11% Increase in Type I Fiber Cross Sectional Area During 12 Weeks of KHCO3 Supplementation) in case you're coming short.
References:

• Aburto, Nancy J., et al. "Effect of increased potassium intake on cardiovascular risk factors and disease: systematic review and meta-analyses." (2013): f1378.
• Blacher, Jacques, et al. "Aortic pulse wave velocity as a marker of cardiovascular risk in hypertensive patients." Hypertension 33.5 (1999a): 1111-1117.
• Blacher, Jacques, et al. "Impact of aortic stiffness on survival in end-stage renal disease." Circulation 99.18 (1999b): 2434-2439.
• Blacher, Jacques, et al. "Pulse pressure not mean pressure determines cardiovascular risk in older hypertensive patients." Archives of internal medicine 160.8 (2000): 1085-1089.
• Cruickshank, Kennedy, et al. "Aortic pulse-wave velocity and its relationship to mortality in diabetes and glucose intolerance an integrated index of vascular function?." Circulation 106.16 (2002): 2085-2090.
• D'Elia, Lanfranco, et al. "Potassium-rich diet and risk of stroke: updated meta-analysis." Nutrition, Metabolism and Cardiovascular Diseases 24.6 (2014): 585-587.
• Gijsbers, L., et al. "Potassium supplementation and heart rate: A meta-analysis of randomized controlled trials." Nutrition, Metabolism and Cardiovascular Diseases (2016).
• Laurent, Stéphane, et al. "Aortic stiffness is an independent predictor of all-cause and cardiovascular mortality in hypertensive patients." Hypertension 37.5 (2001): 1236-1241.
• Malik, Iqbal, et al. "Soluble adhesion molecules and prediction of coronary heart disease: a prospective study and meta-analysis." The Lancet 358.9286 (2001): 971-975.
• Matsuzawa, Yasushi, et al. "Prognostic Value of Flow‐Mediated Vasodilation in Brachial Artery and Fingertip Artery for Cardiovascular Events: A Systematic Review and Meta‐Analysis." Journal of the American Heart Association 4.11 (2015): e002270.
• Shimizu, Motohiro, and Kazuomi Kario. "Review: Role of the augmentation index in hypertension." Therapeutic advances in cardiovascular disease 2.1 (2008): 25-35.
• Tang, Xixiang, et al. "Effect of potassium supplementation on vascular function: A meta-analysis of randomized controlled trials." International Journal of Cardiology (2016).