London, Jan 21 (IANS): Genes play a crucial role over time although environmental factors matter most in the short term, according to a study into social anxiety and avoiding personality disorders.

"The results show a surprisingly high heritability of the long-term risk of developing social anxiety," said Fartein Ask Torvik, a researcher in the department of genetics, environment and mental health at the Norwegian Institute of Public Health (NIPH).

It has long been known that both genetics and the environment play a role in the development of social anxiety, but researchers have been previously unaware of the strong effect of genetic factors over time.

The NIPH researchers followed about 3,000 Norwegian twins to find out more about how mental disorders develop over time, a NIPH statement said.

Twins were studied so that researchers can see the extent to which the disorders are influenced by genetic and environmental factors.

The results for social anxiety and avoidant personality disorder among women are now available. The women were interviewed twice - once when they were in their twenties and once in their thirties.

Just under four percent of participants had social anxiety disorder in their twenties. Another 10 percent had symptoms that did not qualify for a diagnosis.

Ten years later, five percent and just under nine percent respectively had social anxiety disorder or its symptoms. It was not necessarily the same people who had social anxiety in their twenties and thirties.

"The anxiety was less stable than expected. Two-thirds of those who had social anxiety when they were interviewed in their twenties no longer met the diagnostic criteria when they were interviewed ten years later. It appears to fluctuate for individuals, Torvik said.

"However, the prevalence was not lower in the thirties than in the twenties, since other people had the disorder again when they were interviewed" he added.

The events that affect social anxiety in the twenties have little effect in the thirties. The environment has the strongest effect in the short term, and the impact of most experiences will pass.

When researchers looked at the causes of stability and change over time, they found that the genetic risk was persistent and contributed to the stability, while the environment largely contributed to change.

The study was conducted by researchers at the NIPH, with collaborators at the University of Oslo and Virginia Commonwealth University.