July 17 (UPI) -- A new study found the 2011 terrorist attack in Norway by Anders Breivik that killed 77 people resulted in a significant increase in mental health disorders in Denmark.
On July 22, 2011, Breivik bombed a building at the Norwegian parliament in Oslo and then shot and killed 77 adolescents and adults at the Norwegian Socialist Party's youth camp on the Island of Utøya in the deadliest terror attack in the country's history.
Researchers found that the terrorist attacks in Norway had a lasting affect in neighboring Denmark years later, with a significant increase in the amount of people diagnosed with trauma and stress-related disorders such as post traumatic stress disorder, or PTSD.
The study, published July 13 in Epidemiology, was conducted by Aarhus University and the University of Copenhagen.
Researchers analyzed data from the Danish Psychiatric Central Research Register of all psychiatric diagnoses at psychiatric hospitals in Denmark from 1995 to 2012.
The study showed an increase in the number of Danes diagnosed with trauma and stress-related disorders by 16 percent in the 18 months following the terrorist attacks.
"The observed increase in diagnoses of trauma -- and stressor-related disorders, taken together with the fact that we do not see a similar increase at other times or in relation to other diagnoses, indicates that the attacks were indeed the underlying cause," Bertel Hansen, a post-doctoral researcher in the Department of Political Science at the University of Copenhagen, said in a press release.
The team of researchers had previously showed a similar effect in Danes after the Sept. 11, 2001, attacks in the United States.
"We observed the same kind of effect in Denmark following 9/11, but the effect of the Breivik attacks in Norway was four times as strong compared to that of 9/11. We cannot know for certain what causes this difference, but the fact that Danes are closer to Norwegians -- both in a geographical and a cultural sense -- is probably important in that regard. People conceivably felt that 'this could just as well have been us' and that probably amplified the negative effect on mental health in Denmark," Søren Dinesen Østergaard, of the Department of Clinical Medicine at Aarhus University, said.
Researchers believe the media coverage of terrorist attacks plays a part in the type of reaction they are seeing from people in other countries.