But because the research focused on magnesium in food, the authors stopped short of recommending that people take a daily magnesium supplement. It's possible that another aspect of the food is responsible for the finding.
What the results do suggest is that people eat a healthy diet with "magnesium-rich foods such as green leafy vegetables, nuts, beans and whole grains," said lead author Susanna Larsson, a professor at the Karolinska Institutet in Stockholm, Sweden.
Larsson and her colleagues combed through research databases spanning the last 45 years to find studies that tracked how much magnesium people ate and how many of them had a stroke over time.
In seven studies published in the past 14 years, about 250,000 people in the US, Europe and Asia were followed for an average of 11.5 years. About 6,500 of them, or three per cent, had a stroke in the time they were followed.
For every extra 100 milligrams of magnesium a person ate per day, their risk of an ischemic stroke -- the most common kind, typically caused by a blood clot -- fell by nine per cent.
The median magnesium intake for US men and women included in the analysis was 242 milligrams a day (mg/d). The US recommends men and women over age 31 eat 420 and 320 mg/d of magnesium, respectively.
Most of the studies allowed the researchers to rule out other factors, such as family history, from the results, but Larsson told Reuters Health in an email that she cannot say whether other aspects of what the people ate partially or entirely explain the finding.
Because the papers included in the analysis, published in the American Journal of Clinical Nutrition, are so-called observational studies, they also cannot prove that the magnesium is what's actually reducing the stroke risk.
Larsson told Reuters Health that more in-depth studies are needed before researchers can say that.
Dr. Larry Goldstein, director of the stroke center at the Duke University Medical Center in Durham, North Carolina, told Reuters Health that although the findings from reviews like Larsson's are limited, they are consistent with what doctors typically recommend.
"It's a diet that's rich in fruits, vegetables and grains," said Goldstein. "Those are things that have low sodium, high potassium and high magnesium."
"It's again the diet per se, not any one individual component of the diet," Goldstein said.