Here is another reason to stay calm about the threat of terrorism in the United States: the potential health risks of fear may outweigh it. People with a sustained fear of terrorism may have a higher risk of heart ailments, according to a study that was published in the Archives of General Psychiatry in early 2008. The study, which took data from 2,700 Americans whose health was already being tracked for a separate study before September 11, 2001, queried subjects about their fear of terrorism for several years following the attacks.

As reported by John Tierney in the New York Times:

... the most fearful people were three to five times more likely than the rest to receive diagnoses of new cardiovascular ailments. Almost all the people in the study lived outside New York or Washington and didn’t know any victims of the Sept. 11 attacks. But more than a 10th of them reported acute stress symptoms (like insomnia or nightmares) right after the attacks, and over the next three years more than 40 percent said they kept worrying about a terrorist attack affecting themselves or a family member.

Threat Alerts and other Signals May Encourage Fear

The lead researchers in the study conjecture that threat alerts and other signals that remind us of a terrorism threat may contribute to maintaining our fear, thus helping cause not only stress but significant physical ailments. Authorities may send some of these signals unwittingly. Tierney cites a New York City campaign that asks subway riders to "say something" if they "see something suspicious." The signs netted 1,944 calls in a year, a number that New York City trumpeted in subsequent public announcements on the subways.

But, as Tierney notes, "the ads neglected to mention the number of terrorists arrested as a result of the tips: zero."

Similarly, the authors of the study suggested that high threat levels that reminded people of the original attacks may contribute to negative physical as well as psychological effects.