Nearly 73 percent of children who lost a parent in the Sept. 11, 2001, World Trade Center catastrophe developed a psychiatric illness in the years following the event, according to a new study.

More than half (56.8 percent) of the children in the study suffered from an anxiety disorder, chiefly post−traumatic stress disorder (PTSD), which affected nearly three in 10.

The study, which appears in the April 2007 issue of Biological Psychiatry, also found dangerous long−term heightened activity of the brain's "stress−response system" in many children who lost a parent on 9/11.

Levels of psychiatric illness were found to be much higher among bereaved vs. non−bereaved youngsters, despite the fact that many of the bereaved children were receiving psychotherapy to help them cope...

"Continued activation of this system can lead to long−term hypersensitivity to stress as adults and even impact on bone health, since the stress hormone cortisol can harm bone," notes lead researcher Dr. Cynthia Pfeffer, an attending psychiatrist at New York−Presbyterian Hospital/Weill Cornell Medical Center and a professor of psychiatry at Weill Cornell Medical College.

Dr. Pfeffer's team looked at the long−term mental health of 45 children (averaging about 9 years of age) who lost a parent in the 9/11 attacks.

The children were recruited from four months after 9/11 to three years later, then assessed every six months over the following two years.

A control group of 34 non−bereaved children, matched for age and socioeconomic background, was also included in the study.

"This study is unique because it is one of the few well−controlled studies of child bereavement conducted longitudinally, and also because their loss occurred in such a sudden, devastating way," explains Dr. Pfeffer. "We believe that the nature of bereavement does change depending on the type of loss — for example, after a long iness or suddenly and through no fault of the victim, as happened on 9/11."

In each six−month assessment, the team checked for a wide range of psychiatric problems. At the same time, they obtained twice−daily samples of saliva, looking for levels of cortisol, the stress hormone.

Levels of psychiatric illness were found to be much higher among bereaved vs. non−bereaved youngsters, despite the fact that many of the bereaved children were receiving psychotherapy to help them cope, Dr. Pfeffer says.

Besides the high rates of PTSD — which was 10 times that seen in non−bereaved children — the researchers found that 27.3 percent of bereaved youngsters suffered from separation anxiety and 25 percent experienced generalized anxiety, double the rate seen in non−bereaved youngsters. The rate of simple phobias in bereaved children was also double that of non−bereaved children (13.6 percent vs. 5.9 percent).

While the rate of serious depression in bereaved children was twice that of non−bereaved children — 13.6 percent compared to 5.9 percent, respectively — Pfeffer was surprised that children didn't suffer more from depression after losing a parent.

"We usually talk about bereavement being closely associated with sadness and depression, but perhaps the sudden loss of 9/11 led to more anxiety, instead," she says.

A particularly worrying finding came from the cortisol sampling. "Salivary cortisol levels are a marker for the activity of the 'hypothalamic−pituitary−adrenal (HPA) axis,' the body's central responder to stress — our 'fight or flight' mechanism," explains study co−author Dr. Margaret Altemus, associate attending psychiatrist at NewYork−Presbyterian Hospital/Weill Cornell Medical Center and associate professor of psychiatry at Weill Cornell Medical College.

"Usually, this system jumps in action in response to a stress, then slowly goes back down to normal," Dr. Altemus explains. "But we saw elevated cortisol levels in many bereaved children throughout the two−year study. That suggests that the HPA axis remained switched on at a relatively high level."

That could lead to problems down the line, Dr. Pfeffer says, because studies have shown that chronic HPA activation in childhood may make individuals hypersensitive to stressors throughout their lifespan. Chronically elevated cortisol levels can also negatively impact bone health and boost risks for insulin−related dysfunction.

The study suggests that bereaved children, whatever their loss, may need better monitoring and treatment.