PARIS (AFP) - British and US troops deployed to Afghanistan and Iraq face rising pressures on their mental health and family life, according to two investigations that shed light on a key aspect of military "overstretch". Doctors at King's College London assessed regular British military personnel, asking them to fill an anonymous questionnaire about their general health, alcohol use, problems at home and symptoms relating to psychological distress or post-combat stress. Of the 8,686 regular personnel who were randomly selected, 5,547 replied, from all branches -- the Army, Royal Navy, Royal Marines and Royal Air Force (RAF). All had had experience of deployment in the previous three years. Reporting in next Saturday's British Medical Journal (BMJ), the researchers say they found a clear link between mental health problems and the duration of deployment. Those who served longer than the military's guidelines of a maximum 13-month deployment over a three-year period were 55 percent more likely to suffer post-traumatic stress disorder compared to those deployed for shorter periods. This problem increased if the deployment turned out to be unexpectedly long -- a finding that mirrored a previous survey of US troops in Iraq, which discovered that an uncertain date for returning home increased psychological distress. The British study also found a "significant" link between deployment duration and severe alcohol abuse, which increased if the individual had been exposed to combat. However, there was no association between the duration of deployment and any decision to leave the military. The authors, led by public health professor Roberto Rona, say the British military can help reduce the risk of post-traumatic stress by setting down a "clear and explicit policy" on the duration of each deployment. Meanwhile, the Journal of the American Medical Association (JAMA) reports in its latest issue that children of US soldiers experience far higher rates of abuse when their father is deployed on a combat mission. Deborah Gibbs, a researcher with RTI International of North Carolina, and colleagues looked into the cases of 1,771 families of enlisted US troops where there had been documented cases of child abuse, a term that covers physical or emotional maltreatment and neglect. The rate of maltreatment during soldier deployment was 42 percent higher than when soldiers were not deployed. The rate of child neglect by civilian wives was especially high when their husbands were deployed, being almost quadruple that of other times. Britain and the United States are struggling to cope with so-called overstretch of their armed forces. Two major conflicts taking place simultaneously are placing exceptional demands on their land forces in particular, causing commanders to extend the duration of missions and reduce time between deployments.