Geomagnetic storms may influence risk of stroke

More strokes happen when geomagnetic storms are afoot, according to a new review of stroke literature - although it’s not clear what protective measures anyone could take, researchers said.

Geomagnetic storms happen when the Earth’s magnetic field is disturbed by solar winds or coronal mass ejections, which throw out powerful magnetic fields from the sun.

Among more than 11,000 people who had a stroke, the event was almost 20 percent more likely to happen on days with geomagnetic storms, researchers in New Zealand found.

“The results were a big surprise to us,” said lead author Dr. Valery L. Feigin of the National Institute for Stroke and Applied Neurosciences at the School of Rehabilitation and Occupation Studies at Auckland University of Technology.

“What we were particularly surprised with was the size and consistency of the effect of geomagnetic storms on the risk of stroke occurrence, suggesting that geomagnetic storms are significant risk factors for stroke,” Feigin told Reuters Health by email.

The storms can last hours to days, and when strong enough can disrupt satellites and push the aurora borealis much further south than usual, as happened this winter over the United Kingdom.

The electromagnetic upheaval also makes magnetic compasses behave erratically and in 1989, a geomagnetic storm disrupted the Quebec power grid, causing a blackout in the province that lasted nine hours.

Researchers aren’t sure, however, why the storms would be linked to stroke risk.

The review cites six large stroke studies including a total of more than 11,000 patients that took place between 1981 and 2004 in Europe, Australia and New Zealand.

Feigin and his colleagues considered the dates of each participant’s first stroke alongside a record of geomagnetic activity from the same time period from the U.S. National Oceanic and Atmospheric Administration.

For each incident of stroke, researchers compared geomagnetic activity that day with activity on eight other days when the patient did not have a stroke.

According to their results, which are published in the journal Stroke, geomagnetic storms were 19 percent more likely to occur on geomagnetic storm days than on other days.

That is a fairly significant increase in risk, Feigin said, comparing it to the stroke risk associated with taking hormone replacement therapy.

On average, people suffered strokes around age 70, but the connection to geomagnetic storms was stronger for people under age 65.

Over the course of the study, geomagnetic activity didn’t change much from year to year, but it was calmest from 1996 to 1998, which was the period of solar minima in the sun’s 11-year activity cycle, when solar flares and sunspots are least common.