Mild traumatic brain injuries such as concussion can result in increased unemployment rates and productivity loss, according to Auckland University of Technology research.

A study of 245 adults who had a mild TBI four years earlier found that 17 per cent had either left the workforce or reduced their working hours.

The results, published in the Archives of Physical Medicine and Rehabilitation, showed another 16 per cent experienced limitations at work.

These included problems with concentrating, sticking to a routine and managing workload.

Associate Professor Alice Theadom says around 90 per cent of adults will return to employment within two months of a mild TBI.

However, between 22 per cent and 48 per cent of those will experience persistent symptoms, such as headaches, fatigue and difficulties processing information.

Participants who were "taking longer to think" one month after their injury were most likely to be affected by decreased productivity later.

The study concluded that early identification of cognitive difficulties after a TBI and interventions to address those difficulties were needed to help patients to increase productivity.