This study describes the epidemiology of diabetes among First Nations and non-First Nations adults over the longest period reported for a Canadian jurisdiction. We found distinct differences between populations that extend beyond known disparities in the rates of diabetes. Thus, diabetes is a disease of young First Nations adults with a marked predilection for women. In contrast, diabetes is a disease of aging non-First Nations adults that is more common among men. These observations suggest fundamental differences between populations in the mechanisms underlying diabetes; this has widespread implications that are probably also relevant to other indigenous and developing populations.1
Our findings are consistent with reports that used similar methods8,9
to show higher prevalence of diabetes among First Nations people than among non-First Nations people in neighbouring provinces. This difference appears to be at least partly because of higher rates of overweight and obesity among First Nations people.3,19,20
Because of a longer study duration and the inclusion of more detailed incidence data, we have now shown that First Nations people also have markedly different trends and patterns of diabetes than non-First Nations people. Among non-First Nations people, the prevalence of diabetes was identical among men and women in 1980, but it was substantially higher among men by 2005. This corresponded to a divergence in the incidence of diabetes between the sexes, which is possibly related to a greater increase in BMI observed in Canadian men than women during this period.21
Among First Nations people, the prevalence of diabetes was almost twice as high among women as it was among men in the early 1980s, and a large absolute difference has persisted. Although there was considerable annual variation in the incidence (probably partly because of small numbers), the incidence was consistently higher among First Nations women. Differences in incidence between the sexes have diminished over time, however, and it is possible that the large decrease in diabetes incidence among women in the late 1980s was accentuated by the passage of Bill C-31 in 1985. This primarily reinstated young urban First Nations women to the Indian Registry and would have increased the corresponding study denominators.13
Despite very low rates of type 1 diabetes in North American Aboriginal people,18,22
most incident cases of diabetes occurred in young First Nations adults. Furthermore, the consistently higher rates of diabetes among First Nations women than among First Nations men was related to an excess burden of diabetes in women aged 20–49. What could account for this striking sex difference? One possibility is the higher rates of overweight and obesity among First Nations women.19,23
Another factor may be the high rates of gestational diabetes that were present before the significant occurrence of type 2 diabetes in northern First Nations communities;23
gestational diabetes is strongly linked to pre-pregnancy overweight and obesity.24
Because gestational diabetes is a predictor for type 2 diabetes in affected women,25
female populations with high rates of prepregnancy overweight and obesity and gestational diabetes could experience a resultant intragenerational increase in the rate of type 2 diabetes.
Gestational diabetes has also been implicated in an inter-generational “vicious cycle”26
by increasing the risk of type 2 diabetes among the offspring.22,26
This is supported by the early appearance of gestational diabetes among First Nations people23
and its association with increasing rates of high birth weight,27
a predictor of diabetes among First Nations people.28
A recommendation from the Fifth International Workshop on Gestational Diabetes was to clarify the intergenerational diabetogenic role of gestational diabetes.29
We believe that it is equally important to clarify its intragenerational impact and are currently attempting to gain insights into the relative contribution of each through the use of simulation modelling.30
The contrasting demographic features of diabetes in First Nations and non-First Nations people have different implications for prevention, screening, management and allocation of health care resources. We highlight three examples. First, with respect to screening and primary prevention initiatives for First Nations people, our findings support an emphasis on children and young adults.31
We believe that there is sufficient evidence for both an intra- and intergenerational diabetogenic role of gestational diabetes to focus primary prevention initiatives on the time before and during the reproductive years of First Nations women. Programs designed to prevent gestational diabetes, ensure universal gestational diabetes screening, optimize management of diabetic pregnancies and provide follow-up initiatives for women who have experienced gestational diabetes have the potential to reduce the rate of type 2 diabetes in mothers and their offspring.
Second, the large difference in the age of diabetes onset between First Nations and non-First Nations people could contribute to distinct patterns of chronic complications because of differential mortality and differential exposure to the metabolic effects of diabetes. Although speculative, the duration of exposure to diabetes and its interaction with other variables (e.g., quality of diabetes management) might be an important determinant in the relative likelihood of developing specific diabetic complications such as diabetic end-stage renal disease.32
This should also be a priority area for future research.
Finally, the trends reported here indicate that the prevalence of diabetes among both First Nations and non-First Nations people is likely to continue increasing in the foreseeable future, particularly as the large cohort of children and teenagers that make up about half of the First Nations population enter young adulthood. In addition, an earlier “baby boom” among non-First Nations people is approaching the age during which it will also be at the highest risk of diabetes. We are now beginning a period in which two markedly different cohorts will simultaneously experience an increase in diabetes.
Strengths and limitations
The strengths of this study included its duration, use of a validated algorithm to identify diabetes cases,7,16
the use of data for total populations, and the ability to subdivide the population by ethnic background. We are not aware of systematic differences in strategies for diabetes screening or diagnostic criteria between First Nations and non-First Nations people. However, a decrease in diagnostic fasting plasma glucose was widely instituted in 199733
and was followed by an expected rise in diabetes incidence in all study groups.
Limitations of the study included an inability to identify Aboriginal people other than First Nations, reducing the true differences between First Nations and non-First Nations people. Second, identifying cases using administrative data is likely to underestimate the incidence and prevalence of diabetes.8,16
Third, we could not differentiate between type 1 and type 2 diabetes. However, less than 3% of all non-First Nations diabetes incident cases occurred among people aged 20–29, the adult group most likely to develop type 1 diabetes. Furthermore, type 1 diabetes is very uncommon among First Nations people, including children.18,21,22
Thus, inclusion of type 1 diabetes cases would have only marginally increased the rates of diabetes among non-First Nations people and would have likely reduced the true differences between First Nations and non-First Nations people.
Fourth, some prevalent cases of diabetes may have been misclassified as incident cases at the beginning of the study because of delayed diagnosis or limitations of the algorithm. This could have contributed to the initial decline in diabetes incidence observed in all groups. Finally, we were not able to determine the rate of diabetes by location. However, the rates are currently higher in rural areas34
and are consistently lower among northern compared with southern First Nations people.5,8,9
This study shows marked differences in the epidemiology of type 2 diabetes between First Nations and non-First Nations people. Whether this is because of relative differences in the genetics of energy balance interacting with other differences in the environmental determinants of obesity and carbohydrate intolerance is still uncertain. Complicating this further is the emerging possibility that epigenetic phenomena may play a role.35
What is clear is that the rapid appearance of type 2 diabetes particularly among First Nations people and other indigenous and developing populations has been precipitated by environmental rather than genetic factors. Its long-term solution will require effective primary prevention initiatives that are population-based and driven by public health and community initiatives.