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
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
Researchers aren't sure, however, why the storms would be linked to
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
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
On average, people suffered strokes around age 70, but the
connection to geomagnetic storms was stronger for people under age
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.
Feigin pointed out that 2014 is a "solar maximum" year.
"There is preliminary evidence suggesting effects of geomagnetic
storms on blood pressure increase, variations of heart rhythm and
blood clotting abilities, all of which are known risk factors for
stroke," Feigin said, although that's mostly conjecture at this
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Earth's magnetic field differs depending on where you are on the
planet, but geomagnetic storms influence the whole magnetic field,
and based on this review they seem to affect stroke risk in Europe
and Australasia in the same way, he said.
"It's a fascinating idea, at least on that level," said Dr. James Brorson, an expert in the evaluation and treatment of stroke in the
University of Chicago department of neurology. "I wasn't aware that
this was even postulated."
A 19 percent increase in stroke risk is enough to make one sit up
and take notice, but not as large as the risk increase due to
smoking or high blood pressure, he said.
"The idea that geomagnetic storms influence whether or not we
have a stroke almost seems like magical thinking," he said, and it's
certainly too early for people to change their behavior based on the
"Any patient of mine, I would counsel them to by no means worry
about this," Brorson told Reuters Health by phone. "It remains to be seen
whether this holds up."
Besides, he said, geomagnetic storms are not usually very
predictable, and even if they were, there's really nothing anyone
can do to avoid them. The Earth's magnetic field is everywhere,
indoors and out.
Although the authors of the review suggest that people at risk for
stroke could take extra precautions in magnetically turbulent times,
like avoiding stress, excessive alcohol and dehydration, those are
measures people should be taking all the time anyway, Brorson said.
"I don't think that there's practical significance now, but it's
very fascinating," he said.
Stroke, online April 22, 2014.
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