From Medscape.com

Sue Hughes

September 04, 2014

This latest analysis from the WHI is published online in Stroke September 4, with Arjun Seth, BS, Albert Einstein College of Medicine, Bronx, New York, as first author.

The effect was particularly evident for ischemic stroke in women without hypertension, they report. “In the WHI study of older women aged 50-79, those without hypertension who had higher levels of potassium had a 27% reduced risk of stroke than women with low potassium levels,” Seth toldMedscape Medical News.

In the study, higher potassium intake was also associated with a lower risk for small-vessel stroke subtype but was not linked to any reduction in hemorrhagic stroke.

Below Recommended Intake

The researchers also found that in general, this population was well below the recommended daily allowance of potassium. In the United States, this is 4700 mg. The women in the WHI study had average intake of 2600 mg, which is very similar to average US intakes. Only 2.8% of women met or exceeded the 4700 mg recommended intake.

The World Health Organization recommends a potassium intake of more than 3510 mg per day, which may be easier to achieve, but still only 16% of women in this cohort met this requirement.

Senior author, Sylvia Wassertheil-Smoller, PhD, Albert Einstein College of Medicine, Bronx, New York, commented to Medscape Medical News. “In this study, women in the upper quartile had intake over 3200 mg and showed a benefit in terms of reduced stroke versus women with lower intakes. Very few actually achieved the recommended level of 4700 mg.”

She pointed out that it is easily possible to get enough potassium in the diet just by increasing the consumption of fruit and vegetables. Good sources of potassium are potatoes, banana, orange juice, spinach, salmon, raisins, apricots, white beans, and yogurt. A baked potato contains 900 mg of potassium and a banana contains 420 mg.

“So have a banana and a cup of yogurt for breakfast and a meal of salmon, spinach, and a baked potato for dinner and you’re fine,” she said.

The WHI study population consisted of 90,137 postmenopausal women aged 50 to 79 years at enrollment, with no history of stroke. They were followed for an average of 11 years.

Potassium consumption was calculated from food-frequency questionnaires completed by participants at enrollment and at year 3 of follow-up. Stroke was initially identified through self-report at annual visits, and medical records were then requested and stroke was centrally adjudicated by a neurologist. More than 95% of WHI stroke classification was based on MRI or computed tomographic findings.

Results of the current analysis showed that after adjustment for multiple confounders there were significant reductions in stroke and all-cause mortality in women in the highest quartile of potassium intake (>3193.6 mg) compared with those in the lowest (<1925.5 mg).

Table 1. Risk for Stroke and Mortality by Potassium Intake: Whole Population

The stroke reductions were greater in women who did not have hypertension.

Table 2. Risk for Stroke and Mortality by Potassium Intake: No Hypertension

The researchers conclude that: “Because dietary intake of potassium in the United States is well below the recommended intake, these findings are important in suggesting preventive dietary measures to lower the risk of stroke.”

Mechanism: Not Just Blood Pressure

On the mechanism behind the association of potassium and stroke, Dr. Wassertheil-Smoller explained that previous studies showed that potassium has a relationship with blood pressure, but this may not completely explain the reduced stroke rates.

“The association between higher potassium levels and reduced stroke was not seen in the women with hypertension — only in those without raised blood pressure,” she said. “This suggests that there seems to be something else going on here that occurs before hypertension develops. Potassium affects cellular function. It may be doing something that allows the blood vessels to withstand the forces that cause stroke.”

She noted that other studies have looked at potassium and stroke with mixed results, but this study is the largest. “This was an observational study, but we controlled for confounders and we’re never going to have a double-blind randomized trial of potassium intake so this is the best you’re going to get,” she said. “If randomized trials are not feasible, then we have to use evidence from good observational studies. This is a good large rigorous study. It was well conducted and well powered. The ascertainment of stroke was done by neurologists.”

While the WHI study included only women, Dr. Wassertheil-Smoller said the association of high potassium with reduced stroke is also thought to be applicable to men as it has been seen in men in other studies.

Don’t Take Supplements

But she is not recommending people take potassium supplements to boost their intake. “Potassium supplements don’t seem to have the same effect as dietary potassium. And high serum potassium levels can be dangerous. So nobody should start taking any sort of pills based on this study.”

However, she points out that it doesn’t appear to be possible to eat too much potassium.

“Potassium seems completely benign when it comes from dietary sources,” she said. “There isn’t a 1:1 relationship between how much we eat and our blood levels. It is tightly regulated in the body by the kidneys in healthy people. There is a complex relationship with sodium and potassium supplements may upset that balance. We didn’t look at sodium in this study.”

The Women’s Health Initiative program is funded by the National Heart, Lung, and Blood Institute, National Institutes of Health, US Department of Health and Human Services. The authors have disclosed no relevant financial relationships.

Stroke. Published online September 4, 2014