Researchers felt that may come down to other factors not initially taken into account - such as being able to speak another language, in this case te reo, and taking part in cultural activities, including kapa haka.
"Other risk factors for dementia, such as cardiovascular disease and smoking, are also higher among Maori,'' the report says.
"On the other hand, bilingual status is associated with a lower risk of dementia.
"Older Maori have substantial roles involving advanced cognitive activities and, along with kapa haka, cultural activities may provide greater cognitive stimulation and thus preservation of cognition with advanced age of Maori.''
The report was commissioned by the Ministry of Health and produced at the School of Population Health and Faculty of Health and Medical Sciences at the University of Auckland.
Each year, the participants did a screening test for dementia that gives a score of 100. A low score indicated a person was more likely to have dementia.
That first year, 16 per cent were found to have dementia.
Head of Population Health at Auckland University, Professor Ngaire Kerse, said the data looked at who had dementia in the beginning of the study and who developed it over the years.
"We were fully expecting that there would be a higher prevalence of dementia among Maori because there are other disparities and health outcomes.
"So as we were sitting reflecting on how that would be, it's possible that certain lifestyle things protect against the development of dementia.
"Being bilingual is one of the strong protectors. So we know that at least half of this group are fully bilingual and most of them speak a lot of te reo."
She said many of those Maori in the study were active in their communities; holding leadership roles within their whanau and kapa haka groups.
"That, of course, is very stimulating for the memory and stimulating brain activity.
"The literature shows that complicated dance and doing extra study - learning languages - and all of that preserves brain function."
The study provides the only available data on dementia among older Maori.