Geomagnetic Storms Linked to Increased Stroke Risk

April 29, 2014

The most robust evidence yet connecting geomagnetic activity to an increased risk for stroke has been reported from an analysis of 6 large population studies.

"Of 16.9 million new strokes currently happening in the world every year, almost a half million could be attributed to geomagnetic storms," the researchers conclude. The risk is "comparable with the effect of some major well-established modifiable stroke risk factors, such as postmenopause hormone therapy," they add.

They propose that further research should focus on pinpointing the mechanism for this association, which could lead to preventive approaches that could be adopted when periods of intense geomagnetic activity are forecast.

The researchers, led by Valery Feigin, MD, Auckland University of Technology, New Zealand, report their study in a paper published online in Stroke on April 22.

Dr. Feigin told Medscape Medical News that geomagnetic activity has also been associated with increased rates of heart attacks, suicides, and acute psychiatric admissions.

"We have known for ages that geomagnetic storms can shut down electrical stations across many regions and affect satellite navigation equipment, so it is logical that they can also affect human health," he commented.

11-Year Cycles

Dr. Feigin explained that geomagnetic activity occurs in cycles of 11 years in line with solar activity and affect the whole earth. Geomagnetic storms generally last for about 2 to 3 days. In a year of low activity there may be just 2 or 3 storms, but in a year of high activity there could 50 storms — and 2014 is predicted to be a maximal year.

The current study was part of an international collaboration looking at population based stroke incidence in 5 countries: Australia, New Zealand, United Kingdom, France, and Sweden.

The researchers matched these stroke data with information from an international database on geomagnetic activity over 23 years and identified the time lag between peaks in geomagnetic activity and stroke occurrences.

They used a case-crossover design in which each patient is used as his or her own control before the stroke has occurred. This has the advantage of eliminating many confounding risk factors.

Results showed that the maximum risk for stroke occurred a week after a geomagnetic storm. Altogether there was a 19% increase in the relative risk for stroke 1 week after a geomagnetic storm. The more severe the storm, the larger the stroke risk, with the most severe storms associated with a 52% increase in relative risk.

The association was seen across all study populations, age groups, and stroke pathologic types, but younger patients appeared to be affected more by geomagnetic activity. Some subgroups showed a 90% increase in stroke risk with severe geomagnetic storms.

Dr. Feigin commented: "This study has many strengths, including the use of population data which reduces selection bias; and large size, with data from more than 11,000 stroke patients included, which minimizes the chances of false-positives or false-negatives. We also did an individual-participant data analysis, which allowed us to look at particular risk factors for each individual and stroke subtypes as we had neuroimaging data for more than 80% of cases."

Mechanism Unclear?

The mechanism behind the effect is unclear. Dr. Feigin noted, "We don't know what the mechanism is. It has been suggested that geomagnetic activity affects blood clotting process, raises blood pressure, and causes irregular heartbeats in susceptible individuals, so all these factors could contribute. We need more research into the biological mechanism. If we know the culprit we could try and protect against this happening with pharmacological means at the risk periods.

"We are hoping that this study will open up a new area of research into the mechanism by which this is occurring, which could result in new risk reduction strategies. This would involve monitoring a group of individuals with many physiological tests over a period of time, including during a geomagnetic storm, and seeing if we can correlate biological effects."

He would like information on when these geomagnetic storms are going to occur to be common knowledge so that people can take precautions.

"People need to know when these storms are coming," he said. "In time we might have a geomagnetic forecast along with the weather forecast."

He explained that there is not much that can be done to protect ourselves from geomagnetic effects at present apart from enclosing ourselves in a metal case that protects from magnetic energy from all sides, which would not be practical.

 
As it is known that 2014 is a year of high geomagnetic activity, we can expect a higher stroke rate this year. Dr. Valery Feigin
 

But Dr. Feigin points out that people could decide to make behavioral changes to reduce stroke risk, such as decrease stress. This may be especially important during periods of electromagnetic activity. "Because we know the stroke risk is higher during these times we could make a particular effort to minimize other stroke risks."

"As it is known that 2014 is a year of high geomagnetic activity, we can expect a higher stroke rate this year," he concluded. "This is a good motivation to change your lifestyle now in an effort not to be one of those statistics."

Intriguing Report

Asked for comment on these findings, Ralph L Sacco, MD, professor and Olemberg Chair of Neurology, chief of neurology at the Jackson Memorial Miller School of Medicine, University of Miami, Florida, called this an "intriguing report" of the association of geomagnetic storms on stroke risk.

"It is a novel association from a large collection of multiple stroke cohorts that has not been previously reported regarding stroke, but has been suggested for cardiovascular disease," he told Medscape Medical News. "Of course, the exact mechanism is not clear and the association needs replication and further study."

There are prior reports on the variation of stroke risk based on weather conditions, so it is possible that other environmental conditions play a role as a trigger for stroke among those at risk, he added. "The bottom line is that regardless of the geomagnetic conditions, we need to do everything possible to reduce stroke risk by getting more people into ideal cardiovascular health."

Stroke. Published online April 22, 2014. Abstract

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