Association between diabetes and depression: Sex

ARTICLE IN PRESS
Public Health (2006) 120, 696–704
www.elsevierhealth.com/journals/pubh
ORIGINAL RESEARCH
Association between diabetes and depression:
Sex and age differences
W. Zhaoa,, Y. Chena, M. Lina, R.J. Sigalb
a
Department of Epidemiology and Community Medicine, University of Ottawa,
451 Smyth Road, Ottawa, ON, Canada, K1 H 8M5
b
Department of Medicine, University of Ottawa, Canada
Received 17 March 2005; received in revised form 4 February 2006; accepted 5 April 2006
Available online 7 July 2006
KEYWORDS
Depression;
Diabetes;
Cross-sectional study;
Age factor;
Prevalence;
Health survey
Summary Objective: To examine the association between diabetes and the
prevalence of depression in different sex and age groups by analysing the crosssectional data from the National Population Health Survey, conducted in Canada in
1996–1997.
Study design: A total of 53 072 people aged 20–64 years were included in the
analysis. Depression was defined as depression scale X5, based on the Composite
International Diagnostic Interview Short-Form (CIDI-SF). Respondents who answered
the following question affirmatively were considered to have diabetes: ‘do you have
diabetes diagnosed by a health professional?’
Methods: A multiple logistic regression model was used to adjust for potential
confounding effects, and a bootstrap procedure was used to take sampling weights
and design effects into account.
Results: The prevalence of diabetes was much higher in people aged 40–64 years
than in people aged 20–39 years (men: 4.7% vs. 0.5%; women: 3.5% vs. 0.8%,
respectively). In contrast, people aged 20–39 years had a slightly higher prevalence
of depression than those aged 40–64 years (men: 3.1% vs. 2.9%; women: 6.6% vs.
5.4%, respectively). Diabetes was significantly associated with depression in women
aged 20–39 years (odds ratio [OR] ¼ 2.52, 95% confidence interval [CI] ¼ 1.19, 5.32),
but not in women aged 40–64 years (OR ¼ 1.62, and 95% CI ¼ 0.65, 4.06). The
association was not significant in both age groups in men, but it tended to be
stronger in the younger age group.
Conclusions: The data suggest that diabetes is significantly associated with
depression, particularly in young adults.
& 2006 The Royal Institute of Public Health. Published by Elsevier Ltd. All rights
reserved.
Corresponding author. Tel.: +1 613 694 6904; fax: +1 613 241 8120.
E-mail address: [email protected] (W. Zhao).
0033-3506/$ - see front matter & 2006 The Royal Institute of Public Health. Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.puhe.2006.04.012
ARTICLE IN PRESS
Diabetes and depression: sex and age differences
Introduction
Diabetes is one of the most prevalent non-communicable diseases globally. In Canada it is a public
health problem of potentially enormous proportions. The prevalence of physician-diagnosed diabetes is 4.8% among people aged 20 years and older
in Canada.1 With the conservative assumption that
one-third of all cases of diabetes are undiagnosed,
the total number of Canadians with diabetes was
about 1.7 million in 1998–1999.1 About 1.4% of
adults developed diabetes during the 4-year period
between 1994 and 1998.1 The economic burden of
diabetes and its complications in Canada is estimated to be up to $9 billion (US) annually in direct
healthcare costs and indirect costs, including lost
productivity due to diabetes-related illness and
premature death.1
Psychological illness is responsible for considerable disability worldwide. The World Health Organization Global Burden of Disease Survey estimates
that, by the year 2020, major depression will be
second only to ischaemic heart disease in the
amount of disability experienced by sufferers. Many
studies have shown that the risk of depression is
higher in individuals with diabetes than in those
without diabetes.2,3 Known to impair overall
functioning and quality of life,4,5 depression has
additional importance in diabetes because of its
association with poor compliance with diabetes
treatment,4 poor glycaemic control,6 and an
increased risk for micro- and macro-vascular
disease complications.7,8 The presence of concomitant depressive symptoms among people with
diabetes is associated with substantially increased
health economic burden compared with people
with diabetes without depression or depressed
people without diabetes. This is because of the
increased use of emergency care, outpatient
primary care, medical and psychiatric specialty
care, medical inpatient care, and higher prescription costs.3,4
The mental health of young individuals with
diabetes is of particular concern. A meta-analysis
including 20 controlled studies found that the risk
of depression in the diabetic groups was two-fold
higher than that in the non-diabetic comparison
groups.2 This relative risk of depression is greater
than found in most other chronic diseases.3 The
results from previous studies suggest that younger
age was associated with depression,9 and the
primary age of risk for major depression was age
25–40 years in the general population.10 A controlled prospective study found that type 1 diabetes mellitus was associated with more protracted
depressions and a higher recurrence rate among
697
young women, compared with depressed psychiatric patients without diabetes.11 Patients with
type 1 diabetes aged 16–25 years were found to
be more socially isolated than a healthy comparison
group.12 Young diabetic women with depression
had higher ambulatory care use and filled more
prescriptions than their counterparts without
depression.3 However, only 27% of them monitored
blood glucose reasonably well, and only 8% of
them had a glycated haemoglobin concentration
within the optimal range.13 Treatment of depression in people with diabetes resulted in improvements in self-efficacy, self-care behaviours,
glycaemic control, patient satisfaction, and quality
of life.14
The effect of sex and age on the association
between depression and diabetes has not been
previously reported. Monitoring the psychological status of young people with diabetes may
help to identify diabetic patients at risk for
psychiatric disorder, and facilitate prevention or
treatment efforts.11 Identifying the sex and age
difference in the association between diabetes and
depression may be useful for developing targeted
intervention strategies for depression control
and prevention in people with diabetes. We
therefore explored the associations between gender, age, depression and diabetes in a national
cross-sectional survey.
Methods
This analysis was based on cross-sectional data
from the Canadian National Population Health
Survey (NPHS), conducted by Statistics Canada
(Ottawa, Ontario) in 1996–1997. The target population of NPHS was household residents 12 years of
age or more in all provinces, excluding people
living in Indian Reserves, Canadian Forces Bases,
and some remote areas of Quebec and Ontario. The
1996–1997 NPHS was collected mainly by telephone. The NPHS used a multi-stage stratified
sampling design to draw a representative sample
of 95 466 households, and 78 751 households participated in the survey, with a national response rate
of 82%. In all provinces, except Quebec, the Labor
Force Survey design was used to draw the sample.
In Quebec, the Enque
ˆte Sociale et de Sante
conducted by Sante´ Quebec in 1992–1993, with a
two–stage design similar to that of the Labor Force
Survey, was used. In each household, all members
were asked to complete a short general questionnaire, and one person was randomly selected for a
more in–depth interview. The survey included
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698
questions related to the determinants of health,
health status and use of health services.15 This
analysis was based on data from of 53 072 people
aged 20–64 years.
Depression was assessed by the depression scale
from the Composite International Diagnostic Interview (CIDI) Short-Form (CIDI-SF).15 The CIDI is a
structured diagnostic instrument that was designed
to produce diagnoses according to the definitions
and criteria of both DSM-III-R (Diagnostic and
Statistical Manual of Mental Disorders) and the
Diagnostic Criteria for research of ICD-10.15 The
CIDI-SF is a subset of items from CIDI that measures
major depressive symptoms during the previous 12
months. A complete copy of the CIDI-SF questions
and scoring instructions is available from the World
Health Organization website www.who.int/msa/
cidi/index.htm). Depression was considered to be
present when depression scale score was greater
than or equal to 5. Respondents who answered
affirmatively to the question ‘do you have diabetes
diagnosed by a health professional?’ were considered to have diabetes. The association between
diabetes and depression was examined separately
in study participants aged 20–39 and 40–64 years.
We categorized the participants according to
other potential risk factors for depression in the
study, which were similar to a previous report by
Chen et al.16 Self-reported body weight and height
were used to calculate body mass index (BMI):
BMI ¼ weight (kg)/height (m2). BMI values were
categorized into the four groups:o20, 20.0–24.9,
25.0–29.9, and X30.0 kg/m2. Participants in the
low education category had not proceeded beyond
secondary school, and the high education category
included particpants who had been admitted to
college or university, as well as those with a postsecondary school certificate or diploma. Participants were classified into low-, middle-, and highincome groups based on total household income
adjusted for number of household members (appendix A). A positive history of allergy was defined
by an affirmative response to either of the
following questions: ‘do you have any food allergies
diagnosed by a health professional?’ or ‘do you
have other allergies diagnosed by a health professional?’ A regular alcohol drinker was defined as a
person who reported drinking alcoholic beverages
at least once a month. Daily smokers were
respondents smoking cigarettes every day at the
time of survey, former smokers were those smoking
cigarettes daily in the past but not smoking at the
time of survey; otherwise, participants were
classified as non- or occasional smokers. A regular
exerciser was defined as a person who engaged in
physical activities that lasted more than 15 min at
W. Zhao et al.
least 12 times a month. Other variables included in
the analysis were region (eastern, central and
western Canada), immigrant status (yes, no),
marital status (married/common-law/partner, single, widow/divorced/separated), household size
(1, 2, 3, or X4 people), and number of bedrooms
(o3, X3).
The associations between diabetes and depression in different age groups were examined for men
and women separately and jointly. We calculated
the prevalence of depression according to various
factors. Multiple logistic regression models were
used to evaluate the association between diabetes
and the prevalence of depression before and after
controlling the potential confounders. Potential
interactions of diabetes with other factors were
tested at an alpha level of 0.1 in a multiplicative
scale. We calculated the unadjusted and adjusted
odds ratios for depression associated with diabetes
and corresponding 95% confidence intervals by sex
and age groups.
The NPHS used a complex survey design. A design
effect is defined as the ratio of the estimated
variance taking into account the nature of the
survey design to a comparable estimate of variance
based on a simple random sample of the target
population.16 In the present study, the Rao–Wu
bootstrap method was used for variance estimation
to take both the population weights and design
effects into consideration, as described in detail
elsewhere.16 Statistical analyses were carried out
with SAS V8.
Results
The prevalence of diabetes is presented in Table 1.
Diabetes was found to be higher in people aged
40–64 years than in people aged 20–39 years (men:
4.7% vs. 0.5%; women: 3.5% vs. 0.8%, respectively).
In contrast, people aged 20–39 years had a slightly
higher prevalence of depression than those aged
40–64 yeas of age (men: 3.1% vs. 2.9%; women: 6.6
vs. 5.4, respectively) (Fig. 1).
The prevalence of diabetes and depression by the
potential confounders for the relation between
diabetes and depression is also shown in Table 1.
Participants with BMI X 30 kg/m2 had a higher
prevalence of diabetes than participants with lower
BMI; participants with BMIo20 kg/m2 or X30 kg/m2
had higher prevalence of depression than others in
both sexes. Participants with low educational level,
smaller number of bedrooms (o3) and low income
had a higher prevalence of both diabetes and
depression than those with high educational level,
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Diabetes and depression: sex and age differences
699
Table 1 Prevalences (%) of diabetes and depression, by potential risk factors, among individuals aged 20–64 years
based on cross-sectional observations from 1996 to 1997 National Population Health Survey, Canada.
Men
N
Age (years)
20–39
40–64
Region
Eastern
Central
Western
BMI (kg/m2)
o2 0
20–24.9
25–29.9
X30
Unknown
Physical activity
Regular exercise
Not regular
Unknown
Smoking
Non-/ occasional smoker
Former smoker
Daily smoker
Unknown
Drinking
Regular drinker
Not regular drinker
Unknown
Allergy
Any allergy ‘yes’
No or unknown
Educational level
Secondary or lower
Postsecondary or higher
Unknown
Size of household
1 person
2 people
3 people
X4 people
Number of bedrooms
o3
X3
Unknown
Income
Low
Middle
High
Not stated
Marital status
Married
Single
Women
Diabetes
Depression
Case
Case
N
%
N
%
12 991
12 386
89
595
0.5
4.7
448
367
3.1
2.9
1145
14 358
9874
29
406
249
3.4
2.5
2.4
34
445
336
615
8881
11 602
3965
314
12
148
280
235
9
3.2
1.5
2.5
5.7
2.1
14 227
10 524
626
348
301
35
11 232
6398
7655
92
N
Diabetes
Depression
Case
Case
N
%
N
%
14 399
13 296
142
539
0.8
3.5
1049
779
6.6
5.4
3.0
2.8
3.6
1330
15 906
10 459
35
382
264
2.7
2.1
2.0
69
1013
746
5.8
5.5
7.2
40
304
331
139
1
8.9
1.2
1.3
2.7
0.2
3190
12 133
6645
3316
2411
17
143
211
241
69
0.3
0.9
3.1
6.6
2.5
252
742
446
283
105
7.0
5.5
6.5
7.7
3.0
2.8
2.2
3.7
466
346
3
3.0
3.3
0.3
17059
10 250
386
367
301
13
2.0
2.3
3.4
1046
778
4
6.0
6.4
0.3
234
287
159
4
1.8
3.8
2.6
3.4
229
195
390
1
2.0
1.9
5.5
2.6
14 303
6145
7162
85
340
191
148
2
1.9
2.8
1.9
2.2
671
403
754
0
4.0
6.2
10.2
0.0
17 808
7296
273
341
335
8
2.1
3.7
1.6
541
273
1
2.9
3.6
0.1
13 557
13 905
233
167
510
4
0.8
3.4
0.6
934
890
4
6.2
6.0
0.8
5302
20 075
134
550
1.8
2.8
240
575
3.6
2.9
8708
18 987
269
412
2.2
2.0
767
1061
8.7
4.9
9488
15 659
230
320
358
6
3.3
2.2
1.5
309
503
3
2.8
3.2
0.9
10 113
17 391
191
332
341
8
3.0
1.5
3.4
649
1169
10
6.5
5.8
4.1
5048
7504
4788
8037
153
294
119
118
3.2
3.9
2.3
1.7
314
199
120
182
7.6
3.1
2.3
2.0
4514
9106
5517
8558
181
248
124
128
3.6
2.3
2.3
1.4
393
580
394
461
7.9
6.1
6.9
5.0
7635
17 236
506
240
431
13
3.3
2.3
2.6
373
432
10
5.3
2.2
1.6
8482
18 614
599
272
398
11
2.6
1.9
1.4
710
1097
21
6.8
5.8
2.3
2337
5187
12 851
5002
90
147
316
131
3.5
2.4
2.5
2.4
181
211
311
112
6.8
3.5
2.5
1.6
3836
6161
12 131
5567
153
176
221
131
3.7
2.6
1.3
2.1
459
445
643
281
11.6
6.2
4.9
4.5
16 086
6809
482
101
3.0
1.2
335
311
2.2
3.7
17 411
5731
412
88
2.1
1.4
855
487
4.7
7.1
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W. Zhao et al.
Table 1 (continued )
Men
N
Prevalence of depression (%)
Widow, divorced or
separated
Not stated
Immigrant
Yes
No
Unknown
Women
Diabetes
Depression
Case
Case
N
%
N
%
2434
101
3.8
167
8.9
48
0
0.0
2
3919
21 331
127
124
559
1
3.2
2.4
0.5
114
698
3
Diabetes
Depression
Case
Case
N
%
N
%
4476
181
3.4
482
11.3
3.0
77
0
0.0
4
2.8
2.0
3.3
1.8
4311
23273
111
112
565
4
2.7
2.0
2.3
209
1614
5
4.0
6.5
3.3
Discussion
25
20
15
10
5
0
N
20-39
40-64
Male
20-39
40-64
Female
20-39
40-64
Total
Figure 1 The prevalence of depression in subgroups.
Blank, diabetes; black, non-diabetes.
larger number of bedrooms (X3) and middle or high
income.
A higher prevalence of depression in people with
diabetes compared with those without is shown in
Table 2. The difference in the prevalence of
depression between diabetic and non-diabetic
individuals was more evident in younger groups
for both sexes. The prevalence of depression
tended to be higher in women than in men in
all age groups except for the category of younger
diabetic patients, which had a limited sample
size.
Table 2 shows that diabetes was positively
associated with depression, and the association
was stronger among younger adults than among
older adults: the odds ratio was 4.19 (95% CI 0.99,
17.70) in people aged 20–39 years and 2.07 (95% CI
1.08, 3.97) in people aged 40–64 years, respectively. This age difference was seen in both sexes:
the odds ratios were 8.30 (95% CI 0.72, 95.17) for
the younger group and 2.67 (95% CI: 0.90, 7.94) for
the older group in men, and in women they were
2.52 (95% CI 1.19, 5.32) and 1.62 (95% CI: 0.65,
4.06), respectively.
In most studies investigating the association between diabetes and depression, age is usually
adjusted for, and the modifying effect of age is
not examined.9,17 In this paper, we have focused on
the sex and age differences in the association
between diabetes and depression. On the basis of
cross-sectional data from the NPHS in 1996–1997,
our analyses suggest that diabetes was significantly
associated with the prevalence of depression in
young women, and the association tended to be
stronger among younger adults than among older
adults. A meta-analysis including 20 controlled
studies found that the presence of diabetes
doubled the odds of depression.2 The results of a
5-year follow-up study that included patients with
type 1 and type 2 diabetes strongly suggested that
the course of depression in people with diabetes
was perhaps worse than the course of depression
among medically well individuals.18 The lifetime
prevalence of major depression among adults with
type 1 diabetes mellitus and type 2 diabetes
mellitus ranges between 14.4% and 32.5%.6,19
Although some studies that were limited to type 2
diabetes mellitus have shown a positive relationship between type 2 diabetes mellitus and depression,18,19 individuals with type 1 diabetes mellitus
have long been viewed as particularly prone to
depression.11 A 10-year follow-up study10 identified
an effect of type 1 diabetes mellitus on lower
perceived competence in young adults, which could
represent early signs of what may become more
clear-cut presentations of self-esteem problems, as
well as depressive symptoms and illnesses, later in
adulthood. On e study reported that major depressive disorder (MDD) was the most prevalent
psychiatric morbidity among young people with
childhood-onset type 1 diabetes mellitus, with a
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Diabetes and depression: sex and age differences
701
Table 2 Unadjusted and adjusted odds ratios and 95% confidence interval for the prevalence of depression
associated with diabetes by sex and age among people aged 20–64 years based on cross-sectional observations from
1996–1997 National Population Health Survey, Canada.
Age
(years)
Unadjusted OR
95% CI
Adjusted OR*
95% CI
Men
20–39
40–64
9.66
2.28
0.76, 122.41
0.94, 5.54
8.30
2.67
0.72, 95.17
0.90, 7.94
Women
20–39
40–64
2.33
1.76
1.12, 4.85
0.78, 3.94
2.52
1.62
1.19, 5.32
0.65, 4.06
Total
20–39
40–64
4.30
1.87
1.43, 12.91
1.04, 3.37
4.19
2.07
0.99, 17.70
1.08, 3.97
OR, odds ratio; *, adjusted for region, BMI, physical activity, smoking status, drinking status, allergy, educational level, size of
household, number of bedroom, income, marital status and immigrant status.
cumulative probability of 27.5% the tenth year
after diagnosis.11 The prevalence of depression in
children and adolescents with diabetes is two to
three times that of peers without diabetes.7,20
The reasons for the stronger association between
diabetes and depression in people aged 20–39
years, compared with older age groups, are
unclear; however, there are several possible explanations. Different types of diabetes may have
different associations with depression. The mean
age of onset for type 1 diabetes mellitus was 17.3
years, and type 2 diabetes mellitus is most common
in adults over the age of 40 years.18 Younger adults
were more likely to have adolescence-onset diabetes. The prevalence of depression among adolescents with diabetes is three times higher than
that among peers without diabetes.20 The following
reasons may explain the significantly higher odds
ratio in this particular population. First, for
adolescents, the challenge of diabetes, such as,
fear of diabetes-related complications and helplessness in avoiding them, is combined with the
developmental task of adapting to puberty and a
changing body image, peer-group pressure, autonomy from the parents and identity formation.21
This combination of challenges may increase their
risk for a depression episode. Second, the treatment for type 1 diabetes mellitus requires individuals to adhere to a complex set of treatment
regimens, including daily multiple insulin injection,
monitoring blood glucose value, adherence to
specific dietary guidelines and attending regular
medical exams. This heavy burden of treatment
may increase risk for depression. Third, a number
of risk factors have been identified to increase the
likelihood of depression during adolescence, including female gender, family dysfunction and
stressful experience. One stressful experience that
may increase risk for depression in adolescents is
diabetes.21 The history of depressive episode or
stressful experience in adolescence is a risk factor
for depression or recurrence of depression in young
adults with diabetes.21 In addition, the higher odds
ratio in young adults may result from a variety of
inherent differences between type 1 diabetes
mellitus and type 2 diabetes mellitus, including
type of treatment, the influence of the disease on
physical and psychological functioning and the
quality of life resulting from the disease. For
example, patients with type 2 diabetes who are
treated with diet only or oral agents may be less
likely to have depression.22 Our data showed that
the percentage of patients taking insulin was 48.9%
in people aged 20–39 years and 29.7% in people
aged 40–64 years, respectively. Early adulthood is
the developmental period during which individuals
assume a greater degree of independent functioning and take on adult roles; a chronic illness such as
type 1 diabetes mellitus could impede these
aspects of life-cycle development.10 It is also
possible that type 1 diabetes mellitus places
patients at risk for a depressive disorder through
a biological mechanism linking the metabolic
change of diabetes to changes in brain structure
and function.23
The cross-sectional design of the present study
did not permit us to determine the temporal
relation between onset of depression and onset of
diabetes. However, previously published studies
have found that the typical temporal sequence may
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differ between type 1 and type 2 diabetes mellitus.
In a cohort study of adults with diabetes, the mean
age of type 2 diabetes mellitus onset was 37.3
years, and the mean age of depression onset in
patients with type 2 diabetes was 28.6 years.18 It is
possible that depression may lead to lack of
exercise and poor dietary habits, which in turn
increase risk of diabetes. A prospective populationbased study showed that major depressive disorder
predicted the onset of type 2 diabetes.17 In
patients with type 1 diabetes mellitus, the mean
age of diabetes onset was 17.3 years and the mean
age of depression onset was 22.1 years.18 No study
has shown whether the onset of diabetes in childhood or adolescence contributes to the risk for
onset of depression.17
Some studies have observed that a surplus of
hormones antagonizing insulin action is present
during severe depression, including epinephrine,
growth hormone and cortisol.24,25 In a 5-year
follow-up study, poor metabolic control (mean
glycated haemoglobin 11.2%) was reported in the
psychiatrically ill group of people with diabetes at
both the baseline and follow-up evaluations,
compared with a mean glycated haemoglobin of
9.0% in patients with diabetes without documented
psychiatric illness. It was suspected that depression
and diabetes may interact at basic biologic levels,
perhaps in some reciprocal fashion.18
Although some studies indicate that depression
may occur secondary to the hardship of advancing
diabetes,2 a 5-year follow-up study found no
significant differences at baseline and at followup in the prevalence of diabetes complication
between depressed and non-depressed patients
(nephropathy, retinopathy and neuropathy; each
p40:2).18 However, it did not rule out the
possibility that depression may be more closely
related to other unmeasured indices of advancing
disease (e.g. changes in cerebral vasculature or
specific limitations in function (e.g. blindness or
erectile dysfunction).18 In addition, the present
study did not find an association between diabetes
and depression in men; however, owing to the
relatively small sample size and the consequently
limited statistical power of the present study,
studies with large sample size are needed to
further investigate this association in men.
The comorbidity of diabetes and depression
among young people aged 20–39 years is a serious
problem. Depression alone carries significant potential for disability, but, when combined with
W. Zhao et al.
diabetes, the comorbidity carries the potential for
serious long-term consequences. Many investigators have found that people with type 1 and type 2
diabetes with depression have significantly worse
glycaemic control than people with no history of
any psychiatric illness.6,21 Prolonged poor glycaemic control results in more rapid onset and
progression of retinopathy, neuropathy and nephropathy, which have been linked with decreases in
quality of life26,27 and increased mortality.28
Conclusion
This analysis, based on cross-sectional data from
the Canadian National Population Health Survey in
1996–1997, suggests that diabetes is positively
associated with the prevalence of depression, and
the association is stronger among young adults than
among older adults. The age difference is important for several reasons. Depression in young
people with diabetes is associated with a significant
increase in suicide and suicidal ideation.29 The
recurrence and course of depression may be more
severe than that in older groups.11 Young people
with diabetes and depression are likely to have
other comorbid conditions, such as eating disorders, adjustment disorders or anxiety disorders.11
An eating disorder may be life-threatening for
people with diabetes, and early treatment may be
particularly beneficial for young people with
diabetes.11 Therefore, young people with diabetes
should be monitored for psychological status.
Prevention, early diagnosis and early treatment of
depression for them, are extremely important.
Acknowledgements
This research was supported by a grant from the
Canadian Institutes of Health Research and the
Canadian Diabetes Association. Yue Chen is a
Canadian Institutes of Health Research Investigator
Award recipient. Ronald J. Sigal was a Canadian
Institutes of Health Research new Investigator
Award recipient, and currently holds the OHRI
Research Chair in Lifestyle Research.
Appendix A. The classification of income
(Table A1)
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Diabetes and depression: sex and age differences
703
Table A1
Category
Household size
The limit of income
1–4
5 or
1 or
3 or
5 or
more
2
4
more
o$10 000
o$15 000
$10 000–14 999
$10 000–19 999
$15 000–29 999
1 or 2
3 or 4
5 or more
$15 000–29 999
$20 000–39 999
$30 000–59 999
1
3
5
1
3
$30 000–59 999
$40 000–79 999
$60 000–79 999
$60 000 or more
$80 000 or more
Low income
Lowest
Lower middle
Middle income
High income
Upper middle
Highest
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