Self-Reported Diabetes in Northland, New Zealand

There is little published community prevalence diabetes data in Northland, an area at the northernmost part of New Zealand containing 3.8% (140,088) of the total population (1). Māori, the indigenous people, are known to be at increased risk of diabetes (2), and Northland has a Māori population (29%) (1) higher than the national average (14.7%) (3). Hospitalization rates for diabetes are high in Northland, with a standardized relative ratio against the national rate of 1.77 (95% CI 1.55–1.92) (4). The purpose of this study was to assess the prevalence of self-reported diabetes in Northland and to calculate a two-factor (obesity and first-degree family history of diabetes) risk-based prevalence rate for undiagnosed diabetes.

In this study, 360 randomly selected cluster-sampled respondents were selected for personal interviews asking whether they had been diagnosed with diabetes, were receiving regular diabetes checks, had a first-degree family history of diabetes, or had self-reported obesity.

A total of 290 (81%) of 360 potential interviews were conducted. The prevalence of self-reported diabetes was 6%, increasing with age and with no statistical difference overall for sex or ethnicity. The prevalence rate for the two-factor risk-assessed, potentially undiagnosed diabetes pool was a further 4%, with no sex or ethnicity differences and a peak in the 50- to 59-year-old age-group.

National figures from the 1996/1997 National Health Survey show a nationwide diabetes prevalence of 3.7%, with 8.3% for Māori and 3.1% for non-Māori (5). Equivalent data for Northland are sparse. Comparisons with this study and the Northland Diabetes Resource Centre 2001 data show an increase in the overall prevalence rate for diabetes between 2001 and 2003 (from 3.6 to 6.0%, P = 0.0226) and a significant increase in non-Māori with diabetes (from 3.0 to 6.4%, P = 0.0078) (4).

National figures for the size of the undiagnosed diabetes pool have been broadly estimated at between one-third and one-half of all diabetic patients in the community (6). The fact that we found the same order of magnitude as predicted adds support to our study’s validity (6).

Community surveys for diabetes have occurred in other regions, but this is the first Northland survey (7). Self-reported diabetes data generally have inaccuracies, with one study failing to report 11.2% (7). Our study may also underreport prevalence by a similar percentage.

In Northland, the overall diabetes prevalence increase of 66% over 2 years, especially for non-Māori, is substantially higher than the increase of 30% over 10 years predicted by the Ministry of Health (6). Possible explanations would include differential access to medical services (5,8) and increasing diabetes risk factors such as obesity (9). In addition, Māori health providers may have detected the initial “easier to identify” Māori with diabetes, with non-Māori now catching up. Finally, possibly Māori in this study did not self-report diabetes accurately due to cultural aspects of “mana,” or pride and self-worth. However, the lead investigator is Māori, and this was not observed. Most of these explanations also are present in other New Zealand communities. Consequently, further studies are warranted to validate the observed increased incidence of diabetes against predicted incidence and the relative ethnicity changes.