This headline nearly put me off even reading this BBC report, it has some "gems":
Prof Jones said a study undertaken in January and February 2010, found that around 70% of troops reported high levels of unit cohesion, and this was associated with having better mental health.

The report also found that the increased risks encountered in forward operating bases and patrol bases in Afghanistan were off-set by morale and esprit de corps. Yet, psychological problems and severe stress are not unavoidable, especially for those who have been on multiple tours to the region.

The charity Combat Stress say that rates of post traumatic stress disorder in personnel who served in Iraq and Afghanistan are around 4%.

The King's College London study says this increases to 7% for UK frontline troops in Afghanistan. US forces experience higher rates of post-traumatic stress disorder - 13% - due to longer tours of duty, and the use of reservists of a younger age.
Link:http://www.bbc.co.uk/news/health-16973421