2012 University of Alberta - Department of Medicine Research Day, poster presentation by Richard Oster

1. Predictors of A1c among women with a history of gestational diabetes in
Aboriginal communities of Alberta
Richard T. Oster, Ellen L. Toth
Department of Medicine, University of Alberta
Canadian Aboriginal Issues
Database, www.ualberta.ca/
~walld/map.html
Aboriginal Affairs and
Northern Development
Canada, www.ainc-
inac.gc.ca
1. Background
The prevalence of type 2 diabetes is increasing, seemingly unabated (1). Many Canadian
Aboriginal populations suffer type 2 diabetes rates that are 2-5 times higher than the
non-Aboriginal population (2, 3), with Aboriginal women being disproportionately
affected (4). It is believed that a complex combination of social, cultural, environmental
and genetic factors are at play. In attempts to further understand the causes, the possible
contribution of gestational diabetes (GD) has received recent attention. In Aboriginal
populations, it is suggested that GD contributes to a vicious cycle by increasing the risk of
type 2 diabetes in both offspring and mothers (5).
Both the American Diabetes Association and Canadian Diabetes Association now
recommend the use of glycated hemoglobin (A1c) ≥ 6.5% for the diagnosis of diabetes. A1c
indicates the average blood glucose concentrations over the previous 2-3 months and has
been used for decades as a measure of risk for the development of complications and as a
measure of quality of diabetes care. Among people without diagnosed diabetes, there is
increasing evidence demonstrating the usefulness of A1c in predicting potential risk of
diabetes (6).
Given the growing evidence of the ability of hemoglobin A1c to forecast future diabetes,
we sought to examine the predictors of A1c among non-diabetic women (mostly
Aboriginal) with a history of GD in the province of Alberta.
2. Methods
We accessed the databases of three separate community-based diabetes and risk
screening projects. Subjects self-referred from Aboriginal and rural communities in Alberta.
Subjects were screened with clinical exams and portable lab technology between the years
2003-2011. A1c, body mass index (BMI), waist circumference, fasting or random glucose,
total cholesterol, high-density lipoprotein (HDL) cholesterol, blood pressure, as well as the
presence of metabolic syndrome and family history of diabetes was assessed.
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3. Results
A total of 184 adult (≥ 20 years) women with previous GD were screened. Of these
women, 114 were First Nations, 40 were Métis, and 30 were non-Aboriginal. Ethnic
differences in age and percent with low HDL cholesterol were observed.
In the final adjusted model, significant associations remained only for waist
circumference (beta coefficient 0.018; 95% CI 0.007 - 0.031; p = 0.02) and age (beta
coefficient 0.018; 95% CI 0.010 - 0.026; p <0.001). In other words, for a one unit
increase in waist circumference, A1c increases by 0.018 in the model (on average).
Likewise, for a one unit increase in age, A1c increases by 0.018 (on average). Aboriginal
ethnicity was not associated with A1c.
Non-Aboriginal
(N=30)
First Nations
(N=114)
Métis
(N=40)
P-value*
age 47.8 ± 11.78 37.7 ± 10.03 37.5 ± 9.36 <0.001
A1c 5.5 ± 0.49 5.4 ± 0.58 5.6 ± 0.94 0.32
% with undiagnosed
diabetes
3.3%
(0.08-17.22)
5.3%
(1.96-11.10)
12.5%
(4.19-26.80)
0.21
% with hypertension 24.1%
(10.30-43.54)
18.4%
(7.74-34.33)
11.1%
(3.11-26.06)
0.38
% overweight or obese 82.1%
(63.11-93.94)
88.1%
(80.47-93.49)
82.1%
(66.47-92.47)
0.53
% with high waist
circumference
75.9%
(56.46-89.70)
88.6%
(80.89-93.95)
79.0%
(62.68-90.45)
0.13
% with
hypertriglyceridemia
86.7%
(69.28-96.24)
83.3%
(74.94 – 89.81)
81.2%
(65.67-92.26)
0.85
% with low HDL 3.6%
(0.09-18.35)
21.9%
(13.08-33.14)
17.1%
(6.56-33.65)
0.04
% with high total
cholesterol : HDL ratio
3.6%
(0.09-18.35)
15.2%
(7.22-26.99)
17.4%
(6.56-33.65)
0.21
% with metabolic
syndrome
16.7%
(5.64-34.72)
25.4%
(17.75-34.45)
17.5%
(7.34-32.78)
0.42
% with family diabetes
history
71.4%
(51.33-86.78)
68.9%
(59.06-77.69)
86.1%
(70.50-95.33)
0.13
% with sibling diabetes
history
26.7%
(12.28-45.89)
26.3%
(18.51-35.39)
17.5%
(7.34-32.79)
0.51
Characteristics of women with a history of GD. Values are means ± SD or
prevalence (95% CI).
* p-values are for overall differences calculated using ANOVA or Chi-square as appropriate
Beta coefficient P-value
Systolic blood pressure 0.78 0.44
Diastolic blood pressure -0.65 0.52
BMI -0.68 0.49
Waist circumference 2.12 0.03
HDL -0.25 0.80
Total cholesterol 0.35 0.73
Total cholesterol : HDL ratio 0.29 0.77
Age 2.06 0.04
Family history of diabetes 0.38 0.71
Sibling history of diabetes 0.91 0.36
Metabolic syndrome 1.54 0.13
First Nations ethnicity -1.00 0.32
Métis ethnicity 0.54 0.54
Results of simple linear regression analysis (univariate)
Beta coefficient p-value
Waist circumference 0.02 0.02
Age 0.02 <0.001
BMI* -0.01 0.29
Results of final regression model
* BMI was kept in the model as it was a confounder
3. Conclusions
Increasing waist circumference and age are predictive of A1c among women with
previous GD.
Analysis of variance and chi-square tests were used to identify any between group
(ethnicity) differences. Statistical modeling using multiple regression analysis was
conducted to quantify the relationships between A1c and measured variables.
20-29 30-39 40-49 50-59 > 60
4
4.5
5
5.5
6
6.5
7
7.5
Age group
A1c(%)
< 84.9 85-99.9 100-114.9 115-129.9 >130
4
4.5
5
5.5
6
6.5
7
7.5
Waist circumferencegroup
A1c(%)
Average A1c by age group and waist circumference group
4. References
1. Shaw JE et al. Diabetes Res Clin Pract. 2010;87(1):4-14.
2. Young TK et al. CMAJ. 2000;163(5):561-6.
3. King M et al. Lancet. 2009;374(9683):76-85.
4. Dyck R et al. CMAJ. 2010;182(3):249-56.
5. Osgood ND et al. Am J Public Health. 2011;101(1):173-9.
6. Abdul-Ghani MA et al. J Clin Endocrinol Metab. 2011;96(8):2596-600.
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