Participants and study design
The study has a cross sectional design and included 287 patients with T1D. For inclusion and exclusion criteria, included and missing variables, see Figure 1. Inclusion criteria were T1D with ≥1-year duration, in patients 18-59 years of age. Exclusion criteria were pregnancy, severe somatic and psychiatric disorders such as cancer, hepatic failure, end-stage renal disease, Cushing´s disease, severe autoimmune disorders such as systemic lupus erythematosus, psychotic disorders, bipolar disorder, severe personality disorders, severe substance abuse, cognitive deficiency (due to stroke, dementia or mental retardation), or inadequate knowledge of Swedish.
The patients were recruited from one hospital diabetes outpatient clinic in Kronoberg County, Sweden. The patients who attend the clinic every six months for regular follow up visits were consecutively recruited by specialist diabetes physicians or diabetes nurses during a nine-month period, 25 March 2009 to 28 December 2009. The catchment population was 125,000. A questionnaire was used to assess self-reported depression. Blood samples, anthropometrics and blood pressure were collected, supplemented with data from electronic medical records.
Depressive symptoms were assessed by the Hospital Anxiety and Depression Scale - the depression subscale (HADS-D), which consists of 7 statements . Each statement has four response alternatives with scores from 0 to 3. The recommended cut-off level was used to define depression as in our previous research: ≥8 points [28, 29, 31–33]. A major characteristic of HADS-D is that potential symptoms of somatic disease are not included .
Plasma levels of sTWEAK and galectin-3 were measured using commercially available DuoSet ELISA kits (R&D Systems, Minneapolis, Mn, USA) and optimised for human plasma. The analyses were run according to the manufacturer´s instructions. The samples were diluted 1:5 and 1:2, and the intra-assay coefficients of variation were 1.8% and 4.3% respectively for sTWEAK and galectin-3. All samples were run as duplicates. Low sTWEAK levels were defined as <7.1 ng/ml. High galectin-3 levels were defined as ≥2.562 µg/l as in our previous research .
HbA1c and serum lipids were collected after an overnight fast, and analysed with an Olympus automated clinical chemistry analyser with high specificity (Olympus AU®, Tokyo, Japan). High HbA1c levels were defined as >70 mmol/mol (NGSP >8.6%) (corresponding to the 72nd percentile) as in our previous research . The intra-coefficients of variation were for HbA1c <1.2%; total cholesterol <2.1%; HDL-cholesterol <3.0%; LDL-cholesterol <2,6%; and for triglycerides <2.2%.
Creatinine was assayed by an AU2700® instrument (Beckman Coulter, Brea, Ca, USA). The intra-coefficient of variation was <3%.
Anthropometrics and blood pressure
Waist circumference (WC), weight, length and blood pressure were measured according to standard procedures by a nurse. Abdominal obesity was defined as WC ≥1.02 meter for men and as WC ≥0.88 meter for women . General obesity was defined as BMI ≥30 kg/m2 for both sexes .
Episodes of hypoglycemia
A severe episode of hypoglycemia was defined as needing help from another person. Episodes during the last 6 months prior to recruitment were registered.
Smoking and physical inactivity
Smokers were defined as having smoked any amount of tobacco during the last year. Levels of physical activity were assessed by interviews performed by skilled nurses and physicians at the regular follow-up visits. Levels of physical activity performed at work and during leisure time were evaluated. Physical activity was dichotomized into physical inactivity which was defined as less than 30 minutes of moderate activities once a week, and physical activity which represents all other levels of physical activity [28, 30, 33].
CV complications were defined as ischemic heart disease, cardiac failure, stroke or transient ischemic attack.
These were defined as neuropathy, angiopathy, earlier or present diabetes foot ulcer, foot infection, foot deformity, arthropathy, or amputation of the lower limb.
Diabetes retinopathy was defined as non-proliferative or proliferative retinopathy with microangiopathy changes as viewed by fundus photography through a dilated pupil.
Patients used either multiple daily insulin injections (MDII) or continuous subcutaneous insulin infusion (CSII).
Antidepressants were SSRIs (ATC codes N06AB04 or N06AB10); SNRIs (ATC code N06AX16); combined serotonin and norepinephrine reuptake inhibitors (ATC code N06AX21); tricyclic antidepressants (ATC code N06AA04); and/or tetracyclic antidepressants (ATC code N06AX11). The use of antidepressants was dichotomized into users and non-users.
Corticosteroids (ATC codes H02AB01 or H02AB06) were dichotomized into users and non-users.
Lipid lowering drugs (LLD) were defined equal to HMG CoA-reductase inhibitors (statins), (ATC-code C10AA). Indications for LLD were TC >4.5 mmol/l (>1.74 mg/dl) and/or LDL-cholesterol >2.5 mmol/l (>97 mg/dl) according to the Swedish national guidelines in 2009 . The use of LLD was dichotomized into users and non-users of LLD.
Antihypertensive drugs (AHD) included calcium antagonists (ATC codes C08CA01-02); angiotensin-converting enzyme (ACE) inhibitors (ATC codes C09AA-BA); angiotensin II antagonists (ATC codes C09CA-DA); diuretics (ATC codes C03AA03 or C03CA01); and/or selective beta-adrenoreceptor antagonists (ATC code C07AB). Indications for AHD were systolic blood pressure >130 mm Hg and/or diastolic blood pressure >80 mm Hg according to the Swedish national guidelines in 2009 . The use of AHD was dichotomized into users and non-users of AHD.
Analysis of data distribution using histograms revealed that age, diabetes duration, sTWEAK, galectin-3, triglycerides, systolic and diastolic BP, were not normally distributed. Data were presented as median (quartile (q)1, q3), and analyses were performed with Mann-Whitney U test. Fisher´s Exact Test (two-tailed) was used to analyze categorical data, and data were presented as N (%). The 60th, 65th, 70th and 75th percentiles of sTWEAK were tried against depression in a backward elimination multiple logistic regression analysis, and the percentile with the highest association was chosen in the further analyses. Crude odds ratios (CORs) for the associations with depression were calculated. Variables with p ≤0.10 for the CORs, and sex independent of p - value, were entered into multiple logistic regression analyses (Backward: Wald) with depression as dependent variable. The Hosmer and Lemeshow test for goodness-of-fit and Nagelkerke R2 were used to evaluate the multiple logistic regression analysis model. CIs of 95% were used. P <0.05 was considered statistically significant. SPSS® version 25 (IBM, Chicago, Il, USA) was used.