Writing in the journal Stroke, Susanna Larsson, Nicola Orsini and Alicja Wolk from the Karolinska Institute in Stockholm conducted a meta-analysis of prospective studies (where subjects are followed over a prescribed period).
They identified “well-established” nutritional means of lowering blood pressure, including reducing salt intake, weight loss and moderate alcohol consumption, and said “evidence indicates” (Savica et al. 2010) that potassium intake may also reduce blood pressure.
10 relevant prospective studies were selected by Larsson and her colleagues for quantitative statistical analysis.
Assessing the relation between potassium intake and stroke risk across the studies studies – which included recent research by Larsson et al (2011) and Weng et al (2008) – the scientists found a statistically significant inverse association.
Statistically significant results
Discussing their results, the scientists wrote that a 1,000mg/day increase in potassium intake was associated with an 11% reduction in the risk of suffering both a total stroke and ischemic stroke.
However, intake was not associated with hemorrhagic strokes (which result from a ruptured blood vessel in the brain), and “appeared to be limited to ischemic strokes”, which are more common and are caused by the interruption of the blood supply to the brain.
Mechanisms of action cited to explain this effect included animal studies conducted by McCabe et al. (1994), showing that high-potassium diets suppress free radicals and may protect against endothelial dysfunction. The endothelium is the lining of a blood vessel.
“Furthermore, increased dietary potassium has been shown to inhibit vascular smooth muscle cell proliferation in vitro,” the researchers wrote, citing Ishimitsu et al. (1996).
Similar associations were found in studies undertaken in the US, Europe and Asia, and the scientists noted rich dietary potassium sources such as dairy foods, fruits, vegetables, root vegetables and legumes.
Larsson, Orsini and Wolk wrote that the strength of their meta-analysis was the prospective design of studies chosen, which they believed should eliminate selection and recall bias.
However, limitations included the study’s observational design, they wrote, and “the possibility that other factors may account for the observed association cannot be ruled out”.
That said, the scientists noted that most studies within the meta-analysis had been adjusted to account for factors such as smoking, age, body mass index, diabetes history and alcohol consumption.
They also noted that potassium-rich fruits and vegetables are also rich in other nutrients such as vitamin C, folate, magnesium, carotenoids and dietary fibre that may affect stroke risk.
However,“The inverse association between potassium intake and risk of stroke persisted when we restricted the analysis to studies that adjusted for other nutrients.”
For instance, Ascherio et al. (1998) found that potassium supplement use cut stroke risk after adjustment for history of hypertension, the scientists wrote.
“This finding provides further support for the fact that potassium intake and not other nutrients explains the observed finding in this meta-analysis,” they concluded.
The current EU Recommended Daily Allowance (RDA) for Potassium is 2,000mg/day, under the terms of Directive 2008/100/EC.
Published online ahead of print doi: 10.1161/STROKEAHA.111.622142
Title:“Dietary Potassium Intake: A Dose–Response Meta-Analysis of Prospective Studies”
Authors: S.Larsson, N.Orsini, A.Wolk