This exploratory and cross-sectional study was approved by the National Hospital Organization (NHO) Central Research Ethics Committee (R2-0117002) and performed in accordance with the Strengthening the Reporting of Observational Studies in Epidemiology guidelines.
Participants and settings
Between February 2020 and March 2022, we enrolled adult patients with IAH from the NHO collaborating centers in Japan. The following seven institutions participated in this study: NHO Mie Hospital, NHO Kyoto Medical Center, NHO Osaka National Hospital, NHO Himeji Medical Center, NHO Hyogo-Chuo National Hospital, NHO Okayama Medical Center, and NHO Kokura Medical Center. The participants were divided into IAH and non-IAH (control) groups.
Patients with T1D, with a diabetes duration of ≥1 year, aged ≥20 years, and who attended a collaborating center were included in the study. Meanwhile, patients who received non-insulin therapy, were using anti-dementia drugs, and were considered as inappropriate cases as judged by the research director or coordinators were excluded.
Diabetic complications
Diabetic retinopathy, diabetic nephropathy, and DPN were managed by certified diabetologists according to the treatment guidelines for diabetes in 2018–2019. Diabetic retinopathy was assessed by an ophthalmologist using retinal photography. Retinopathy was classified as absent, simple, preproliferative, or proliferative. Nephropathy was classified into stages 1–5 based on the estimated glomerular filtration rate, presence of albuminuria, or hemodialysis stage [16]. DPN was considered present based on the criteria after the diagnosis of diabetes and excluded polyneuropathy, except for diabetic polyneuropathy, which was determined to be positive in the presence of at least two of the following three criteria: 1) subjective symptoms (numbness, pain, or dysesthesia in the bilateral lower extremities), 2) decreased or absent bilateral Achilles tendon reflexes, and 3) diminished bilateral vibratory sensation in the malleolus medialis (<10 s using a tuning fork at 128 Hz) [17]. The coefficient of variation of the R-R intervals (CV-RR) was calculated automatically using a computed analyzer that collected 100 R-R intervals and divided the standard deviation by the mean value. A CV-RR of <3% was considered indicative of diabetic cardiac autonomic neuropathy [18]. The mean corrected QT (QTc) interval was calculated using Bazett’s formula, and a QTc interval of >440 ms was considered prolonged [19]. Data on HbA1c level, glycated hemoglobin (GA) level, liver enzyme (aspartate aminotransferase, alanine transaminase, and gamma-glutamyl transferase) levels, and lipid profiles were collected from the patients’ medical records. Furthermore, the GA/HbA1c ratio, which reflects glucose variability, was calculated by dividing the GA level by the HbA1c level [20].
RSH, IAH, and hypoglycemic symptoms
SH was defined as an event requiring assistance from another individual to actively administer carbohydrates or glucagon or to take corrective action [21]. RSH was defined as two or more episodes of SH in 1 year [22]. The IAH was determined using the gold standard method [23]. The Gold’s questionnaire constitutes a single question (“Do you know when your hypoglycemia is commencing?”), and the patients respond using a 7-point Likert scale, with scores ranging from 1 (“always aware”) to 7 (“never aware”). In the gold standard method, a score of 4 or higher implied the presence of IAH. Hypoglycemic symptoms were evaluated using the Edinburgh Hypoglycemia Scale [24,25]. This questionnaire comprises 11 key symptoms (sweating, palpitations, shaking, hunger, confusion, drowsiness, odd behavior, speech difficulty, incoordination, nausea, and headache), which are evaluated using a 7-point Likert scale, with scores ranging from 1 (“not at all”) to 7 (“very severe”), and divided into three domains (neuroglycopenic, autonomic, and general malaise). The self-reported number of SH episodes in the preceding year, defined as “hypoglycemia that the patient was unable to treat on his or her own,” was also assessed.
Diabetes-related distress and hypoglycemia problem-solving abilities
Diabetes-related distress was assessed using the Problem Areas in Diabetes (PAID) questionnaire. Each item on the PAID questionnaire was scored from 0 (“no problem”) to 4 (“serious problem”). All 20 scores were summed and multiplied by 1.25, with a total score of 0–100 points. Higher scores indicate greater diabetes-related distress; a cut-off score of ≥40 indicates high level of distress [26,27]. Fear of hypoglycemia was assessed using the Hypoglycemia Fear Survey (HFS), adapted for use in Japan [28,29]. The HFS has two subscales: the HFS-B (behavior subscale) and HFS-W (worry subscale). The items are rated on a 5-point Likert scale, with scores ranging from 0 (never) to 4 (always). Higher scores indicated a greater fear of hypoglycemia. Health-related quality of life was assessed, and the utility index was calculated using the European Quality of Life-5-Dimension (EQ-5D) questionnaire [30,31]. This questionnaire has five dimensions: mobility, self-care, usual activities, pain/discomfort, and anxiety/depression. The EQ-5D-3 level, which assesses each dimension based on three levels of severity (e.g., “no problem,” “some problems,” or “unable”). Hypoglycemia problem-solving abilities were assessed using the Hypoglycemia Problem-Solving Scale (HPSS) [12]. The HPSS has 24 items and seven subscales: problem-solving perception, detection control, identifying problem attributes, setting problem-solving goals, seeking preventive strategies, evaluating strategies, and immediate management.
Lifestyle factors
Self-administered questionnaire data regarding lifestyle behaviors (current smoking, regular exercise, dietary habits, drinking habits, and sleeping habits) were collected using a standardized questionnaire from the Specific Health Check and Guidance System [32]. Three items were related to exercise habits: 1) regular exercise (≥2 times/week of exercise ≥4 METs/h), 2) active physical activity (≥23 METs × h/week), and 3) walking pace (rapid or not rapid), which is an indicator of physical fitness. Excessive drinking was defined based on the answers to questions on drinking habits: “occasionally or every day” and “≥180 mL of sake (equivalent to ≥20 g of alcohol).” Sleep debt was defined as the difference between the self-reported total weekday and weekend sleep hours of at least two hours [33]. Healthy lifestyle behaviors included consumption of fruit, fish, and milk; level of exercise; avoidance of smoking; moderate alcohol intake; and moderate sleep duration [34].
Data analyses
Qualitative variables were compared using the Fisher’s exact test . As the analyzed quantitative variables were not normally distributed, comparisons were conducted using the Mann–Whitney U test for two groups and the Kruskal–Wallis test for three or more groups. The normality of the variable distribution was verified using the Shapiro–Wilk test. Logistic regression was used to estimate the odds ratios (ORs) and their corresponding 95% confidence intervals (CIs). Patients with RSH were divided into three groups: non-SH, solitary SH, and RSH. Multiple comparisons were performed using one-way analysis of variance followed by Tukey’s post-hoc test. Trends were assessed using the Jonckheere–Terpstra test. A P value of <0.05 was considered significant. Cronbach’s alpha coefficient and mean interitem correlations were used to measure the internal consistency of the questionnaires. Patients with missing data were excluded from the analysis. The analysis was conducted using R version 4.1.2. We acknowledged and cited our previous article on description method [35].