A new US study has found that nearly a third of Gulf war veterans treated by Veterans Affairs (VA) between 2001 and 2005 returned from Iraq or Afghanistan with mental health difficulties.

The study is published in the Archives of Internal Medicine.

Researchers at the University of California, San Francisco and the San Francisco VA Medical Center reviewed data collected on 103,788 veterans, half of whom were National Guard or Reserves.

Just over half of the veterans were under the age of 30, with females numbering 13 per cent and minorities around 33 per cent.

Dr Karen H. Seal and colleagues assessed the types of of mental health and psychosocial problems reported in the vets using the International Statistical Classification of Diseases and Related Health Problems (ICD-9) clinical modification system designed by the World Health Organization (WHO).

They found that of the total, 32,010 (31 percent) had some form of measurable "mental health problem" when they broadened the definition to include psychosocial behavioural problems as well as mental health.

One quarter, that is 25 per cent (25,658) of the 103,788 veterans who returned from Iraq or Afghanistan to be treated by the VA in the four year period received at least one mental health diagnosis.

Of these 25,658 vets, over half were diagnosed with two or more mental health problems.

Post-traumatic stress disorder (PTSD) was the most common mental health problem, affecting 13,205 vets (52 per cent of the 25,658).

That's just under the 15 per cent figure estimated for Vietnam War vets but it is nearly four times the prevalence in the population at large.

The researchers found "minimal" race and gender effects.

Overall, the younger veterans (18 to 24) were five times more likely to have PTSD than the older ones (40 and over). The researchers suggest this could be because the younger ones tend to be lower rank and have more combat exposure.

Dr Seal and her team suggested this study shows a need to improve the "primary prevention of military service-related mental health disorders, particularly among our youngest service members".

They conclude that "Targeted early detection and intervention beginning in primary care settings are needed to prevent chronic mental illness and disability."

They emphasize that the study only included those Operations Enduring Freedom and Iraqi Freedom vets that were in receipt of VA services and the findings do not necessarily represent all vets who served in the Gulf War.

PTSD occurs when someone experiences or witnesses a life-threatening traumatic event and has a prolonged reaction that does not subside. It is characterized by symptoms such as flashbacks, hypervigilance, insomnia, nightmares, and numbness of feelings or emotions. PTSD can also manifest after the event, sometimes years, and is known as delayed PTSD.

In the longer term PTSD can lead to depression, general anxiety disorder, bipolar disorder, and/or a range of other physical and mental health problems such as substance abuse, and thinking and memory problems.