Prolonged periods of deployment among the UK's armed forces have fallen since the introduction of the "Harmony Guidelines" to limit tours of overseas duty - which might have led to a reduction in mental health problems, new research published in The Lancet Psychiatry journal suggests.

Researchers from King's College London estimate that this drop in the number of troops experiencing prolonged tours of duty might have prevented 138 cases of post-traumatic stress disorder (PTSD), 453 cases of psychological distress, 309 cases of multiple physical symptoms, and 490 cases of alcohol misuse between November 2004 and September 2009.

In 2007, research by the King's College London Centre for Military Health Research showed that long operational tours - more than 13 months within a 3-year time period (the maximum recommended time limit set by the UK Government and known as the Harmony Guidelines) - were linked to serious mental health problems, alcohol problems, and family difficulties.

In this study, Roberto Rona, Professor of Public Health Medicine at King's College London and colleagues re-examined whether length of deployment above these guidelines and frequency of deployment over 3 years had an effect on mental health. They assessed a random sample of 3982 regular military personnel (Army, Royal Navy, Royal Air Force, and Royal Marines) who had been on overseas tours during the 3 years prior to completing a questionnaire between November 2007 and September 2009, asking about their health including symptoms of post-traumatic stress disorder (PTSD), psychological distress, alcohol consumption, and problems at home.

The researchers found that breaching the Harmony Guidelines by deploying for 13 months or more over a 3-year period almost halved from 22% in March 2005 to 12% in May 2008*.

Being deployed for more than 13 months over 3 years was associated with a significantly increased risk of developing PTSD or subthreshold PTSD, multiple physical symptoms, problems at home, and relationships and family problems compared to those deployed for shorter time periods, but not with psychological distress or harmful drinking. For example, rates of PTSD including subthreshold PTSD were around 12% in those deployed above the 13 month limit, compared with 6% among those who spent less than 5 months in conflict (see table 2 page 4).

Importantly, the number of deployments was not associated with worse mental health or problems at home.

According to Professor Rona, "The Harmony Guidelines can prevent mental illness in the UK Armed Forces and, since 2006, their introduction has prevented deployment of more personnel for longer than recommended in the guidelines. Monitoring of cumulative length of deployment could prevent an increase in levels of stress and mental illness in the UK military."**

Writing in a linked Comment, Professors Robert Ursano, David Benedek, and Gary Wynn from the Uniformed Services University School of Medicine, Bethesda, Maryland, USA, say, "Further work is needed, now and certainly for any future conflicts. To examine the subtleties of length of deployment and number of deployments needs a sample powered to examine the interaction of these two variables. For example, four deployments of 3 months each are different to a continuous 1 year deployment... A deep understanding of dwell time [time between deployments for recovery], in addition to length and number of deployment, can help inform policies to better protect the health of service members."