A team from Auckland's University of Technology found that rates of traumatic brain injury, which can be caused by any kind of knock to the head, are 30 to 40 per cent higher than in Europe or North America.
Director of the University's Institute for Stroke and Applied Neuroscience, Professor Valery Feigin, says severe cases are easy to pick, but mild traumatic brain injury can go unnoticed, with potentially severe consequences.
"Mild traumatic brain injury is usually characterised by very short loss of consciousness or memory loss to the event of the injury, which is lasting less than 24 hours," he told Radio Australia's Pacific Beat.
Professor Feigin says undiagnosed mild cases can lead to mild memory difficulties, dementia, Alzheimer's disease and even stroke.
Professor Feigin's team completed the study of 170,000 residents in the north island region of Waikato.
The study canvassed service providers, sporting associations, schools and other community groups.
Estimates show that 36,000 New Zealanders are affected by new traumatic brain injuries every year - a much higher number than those affected by heart attack or stroke.
The study found that children and young adults accounted for two-thirds of all TBI cases, with Maori and people in rural communities over-represented.
Falls were the biggest cause of brain injury.
Professor Feigin says mild TBI can also result in changes in personality.
"They may be socially disintegrated as a result of brain injury and this is a much bigger problem than just immediate effects of the mild traumatic brain injury," he said.