Participants and study design
The study has a cross sectional design and included 287 patients with T1DM. For inclusion and exclusion criteria, included and missing variables, see Figure 1. Inclusion criteria were T1DM 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 the Swedish language [29, 31–36]. As patients with these disorders were excluded, no specific medications for any of these disorders were used by the included patients. Patients using systemic corticosteroids were excluded .
The patients were consecutively recruited from the largest of two specialist diabetes hospital outpatient clinics where all adult patients with T1DM are treated in Region Kronoberg, Sweden [29, 31–36]. 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 [29, 31–36]. 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. Data collection was performed at baseline of a randomized controlled study (RCT) for patients with diabetes, Hemoglobin A1c (HbA1c) > 70 mmol/mol and psychological symptoms (ClinicalTrials.gov: NCT01714986) , and the study is one out of several baseline analyses [29, 31–36]. We adjusted for age, sex, diabetes duration, galectin-3, metabolic variables, serum (s)-creatinine, smoking, physical inactivity, medication, and cardiovascular complications.
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: ≥ 8 points as in our previous studies [29, 31–36, 38]. HADS was developed to detect symptoms of depression and anxiety in patients repeatedly searching medical care for somatic complaints, where no somatic disorders were confirmed that could explain their symptoms . No higher levels of emotional awareness are necessary to respond to the statements. A major characteristic of HADS-D is that potential symptoms of somatic disease are not included . According to previous research HADS-D is a useful instrument for detecting symptoms of depression, both at an individual and a collective level, and has been demonstrated to have a good reliability and discriminant validity .
Plasma levels of sTWEAK and galectin-3 were measured using commercially available DuoSet enzyme linked immunosorbent assays (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. High galectin-3 levels were defined as ≥ 2.6 ng/ml as in our previous research .
HbA1c and serum-lipids were collected after an overnight fast and they were analysed with an Olympus automated clinical chemistry analyser (Olympus AU®, Tokyo, Japan). (corresponding to the 72nd percentile) as in our previous research . High HbA1c levels were defined as > 70 mmol/mol (NGSP > 8.6%). The intra-assay 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%.
S-creatinine was assayed by an AU2700® instrument (Beckman Coulter, Brea, Ca, USA). The intra-assay 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. Body Mass Index (BMI) (kg/m2) was calculated. Abdominal obesity was defined as WC ≥ 1.02 meter for men and as WC ≥ 0.88 meter for women as in our previous studies [29, 31–36, 40].
A ratio between triglycerides and HDL-cholesterol was calculated for the estimation of insulin resistance .
Episodes of hypoglycemia
A severe episode of hypoglycemia was defined as hypoglycemia to such a degree that the patient needed help from another person. Episodes during the last 6 months prior to recruitment were registered [29, 31–36].
Smoking and physical inactivity
Smokers were defined as having smoked any amount of tobacco during the last year. 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 [29, 31–36].
Cardiovascular complications were defined as ischemic heart disease, cardiac failure, stroke, or transient ischemic attack [29, 31–36].
Patients used either multiple daily insulin injections (MDII) or continuous subcutaneous insulin infusion (CSII) [29, 31–36].
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 [29, 31–36].
Lipid-lowering drugs and indications for treatment of hyperlipidemia
Lipid-lowering drugs were hydroxy-methylglutaryl coenzyme A (HMG-CoA)-reductase inhibitors (statins), (ATC-code C10AA). The use of lipid-lowering drugs was dichotomized into users and non-users of lipid-lowering drugs [29, 31–36].
Indications for lipid-lowering drugs 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 .
Antihypertensive drugs and indications for treatment of hypertension
Antihypertensive drugs 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). The use of antihypertensive drugs was dichotomized into users and non-users of antihypertensive drugs [29, 31–36].
Indications for antihypertensive drugs were systolic blood pressure > 130 mm Hg and/or diastolic blood pressure > 80 mm Hg according to the Swedish national guidelines in 2009 .
Analysis of data distribution using histograms revealed that age, diabetes duration, sTWEAK, galectin-3, triglycerides, systolic and diastolic blood pressure, 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 analyse categorical data, and data were presented as N (%). The 60th, 65th, 70th and 75th percentiles of sTWEAK and log-transformed sTWEAK (Lg10) were tried against depression in a backward elimination multiple logistic regression analysis, and the percentile with the highest association was defined as low sTWEAK and was therefore used in the further analyses. Crude odds ratios (CORs) for the associations with depression and with low sTWEAK (< 7.2 ng/ml) were calculated for all included variables. Variables with p < 0.10 for the CORs were entered into multiple logistic regression analyses (Backward: Wald) with depression and low sTWEAK as dependent variables . The Hosmer and Lemeshow test for goodness-of-fit and Nagelkerke R2 were used to evaluate each multiple logistic regression analysis model. Confidence intervals (CIs) of 95% were used. P < 0.05 was considered statistically significant. SPSS® version 25 (IBM, Chicago, Il, USA) was used.