MONDAY, Feb. 29, 2016 (HealthDay News) -- People with a history of fainting may be almost twice as likely as others to get into a car crash, a new study finds.
The researchers say the study results suggest officials should consider fainting among various risk factors when they decide who can or can't drive legally.
"This risk is small but it raises important questions about policies towards driving," said study lead author Dr. Anna-Karin Nume, a graduate student with the cardiology department at Copenhagen University Gentofte Hospital in Denmark.
The findings don't prove a direct connection between fainting spells and car crashes, and it's not clear who caused the accidents in the study. Still, a history of fainting raises the danger that a driver could lose consciousness on the road, experts say.
According to Nume, an estimated 35 percent of people faint during their lives. "It is common in both young and older persons, but the cause usually differs," she said. "Although fainting is usually benign, it could be caused by underlying heart conditions."
About one-third of patients who have fainted with have a subsequent episode within three years, according to the researchers.
In the United States, rules vary among states about whether residents can continue to drive after fainting.
According to the American Diabetes Association, Wyoming, for example, will cancel driving privileges if notified by a doctor that a patient has a disorder that's caused a lapse in consciousness. California distinguishes between fainting cases that are one-time incidents and those that could recur.
For the new study, researchers tracked more than 41,000 adults in Denmark, average age 66, who suffered a first-time diagnosis of fainting between 2008 and 2012. The authors compared their experiences to those of 4.2 million other Danish residents, average age 45.
After the researchers adjusted their statistics for factors such as age, they found that those with fainting episodes were nearly twice as likely to have gotten into crashes.
Over five years, 8 percent of those aged 18 to 69 who'd been treated for fainting got into crashes, compared to 5 percent of the general population.
But the study results suggest that age and health may play roles. Those treated for fainting were more likely to be 70 or older (37 percent compared to 13 percent of the general population), and more than one-third had heart disease compared to 10 percent of the others.
Those treated for fainting were also more likely to suffer from conditions such as diabetes or alcoholism and take anti-anxiety medications. There was little difference in fainting rates between men and women.
It's not clear, however, who was at fault in the accidents. "The records we have do not contain enough detail to work out exactly what happened in these accidents. Our study looked at the larger picture and did not capture this level of detail," Nume said. "But it would be worth doing a study to interview patients after the accidents and identify the sequence of events."
It's also not clear whether certain disorders that cause fainting are more dangerous to drivers. "We don't know which diagnoses have clear warning symptoms that allow plenty of time for the driver to compensate, get off the road safely, and subsequently continue normally," said Dr. Donald Redelmeier, senior core scientist with the Institute for Clinical Evaluative Sciences in Toronto.
Redelmeier, co-author of a commentary accompanying the study, also believes overconfidence may be a factor if drivers don't take precautions despite their fainting history.
At age 70 in Denmark, patients undergo mandatory driver's license screenings from their doctors, according to background notes with the study.
Nume said the results can be helpful as officials consider guidelines about who should and shouldn't be allowed to drive. But, she said, fainting shouldn't be the only factor considered.
Redelmeier agreed the findings should remind physicians to consider driving safety when they treat patients who have fainted.
The study appears in the Feb. 29 issue of JAMA Internal Medicine.
For more about fainting, see the U.S. National Institute of Neurological Disorders and Stroke.