An Evaluation of the Effect of Vitamin D Supplementation on Depressive Symptoms Among Chinese Early Adolescents

Depressive symptoms are evaluated by the Chinese version of Beck Depression Inventory (BDI-II-C). The measured outcome was the total BDI-II-C scores. Each of the 21 items can be scored as 0, 1, 2, or 3 points. The range for the BDI-II-C score is 0-63 points; higher scores indicate worse depressive symptoms. Change in BDI-II-C scores from pre to post-intervention were compared between randomized groups, which was the primary outcome of this study.

Depressive symptoms are assessed by BDI-II-C. Data from all time points will be used to determine the mean differences in change in depressive symptoms scores over all follow-up by randomized treatment.

Patient Health Questionnaire-9 (PHQ-9) is a 9-item instrument for measuring the severity of depression. The PHQ-9 is based on the diagnosis of the Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV) depressive disorders. Each of the 9 items can be scored from 0 (not at all) to 3 (nearly every day), and the total scores of PHQ-9 can range from 0 to 27. The higher score indicates more depressive symptoms. It can be administrated repeatedly and can reflect improvement or worsening of depression in response to treatment. Data from all time points will be used to determine the mean differences in change in depression scores over all follow-up by randomized treatment.

Sleep quality is evaluated by the Pittsburgh Sleep Quality Index (PSQI). In scoring the PSQI, seven component scores are derived, each scored 0 (no difficulty) to 3 (severe difficulty). The component scores are summed to produce a global score (range 0 to 21). Higher scores indicate worse sleep quality. Data from all time points will be used to determine the mean differences in change in sleep quality scores over all follow-up by randomized treatment.

Suicidal ideation will be asked by the item 'In the past three months, have you ever thought about killing yourself?'. The responses will be classified as yes or no.

Anxiety symptoms will be assessed by the Generalized Anxiety Disorder 7-item scale (GAD-7). GAD-7 has seven items and assess the severity of the severity of generalized anxiety symptoms over the past two weeks. Response options include "not at all", "several days", "more than half the days" and "nearly every day". In scoring the GAD-7, each of seven items scored 0 (not at all), 1 (several days), 2 (more than half the days), and 3 (nearly every day). The total scores are calculated and range from 0 to 21. Higher scores indicate worse anxiety symptoms. Data from all time points will be used to determine the mean differences in change in sleep quality scores over all follow-up by randomized treatment.

Resilience will be evaluated by the Connor-Davidson Resilience Scale (CD-RISC). The CD-RISC consists of 25 items, which are evaluated on a five-point Likert scale ranging from 0 to 4: not true at all (0), rarely true (1), sometimes true (2), often true (3), and true nearly all of the time (4) - these ratings result in a number between 0-100, and higher scores indicate higher resilience. Data from all time points will be used to determine the mean differences in change in resilience scores over all follow-up by randomized treatment.

Hopelessness will be evaluated by the Beck Hopelessness Scale (BHS). The BHS consists of 20 dichotomous "true/false" items that aims to assess three major aspects of hopelessness (i.e., feelings about the future, loss of motivation, and expectations). Higher total scores indicate greater hopelessness (range 0-20). Data from all time points will be used to determine the mean differences in change in hopelessness scores over all follow-up by randomized treatment.

Emotional and behavioral problems are assessed by the Pediatric Symptom Checklist-17 (PSC-17). The PSC-17 consists of 17 items, and is categorized as three subscales (5 items on internalizing subscale, 5 items on attention subscale, and 7 items on externalizing subscale). The responses are 0 ("Never"), 1 ("Sometimes") and 2 ("Often"). The total score of the PSC-17 is calculated, and ranges from 0 to 34. Higher scores can indicate an increased likelihood of a behavioral health disorder being present. Data from all time points will be used to determine the mean differences in change in internalizing, attention and externalizing scores over all follow-up by randomized treatment.

Loneliness will be measured by the short-form University of California, Los Angeles (UCLA) Loneliness Scale (ULS-8). The total score ranges from 8 to 32 points, with higher scores suggesting a higher degree of loneliness. Data from all time points will be used to determine the mean differences in change in loneliness scores over all follow-up by randomized treatment.

The Emotion Regulation Questionnaire for Children and Adolescents (ERQ-CA) is a 10-item scale to measure respondents' tendency to regulate their emotions and the total scores will be used in this study. Items are rated on a 5-point Likert-type response scale (1=strongly disagree, 2=disagree, 3=half and half, 4=agree and 5=strongly agree). The total score ranges from 10 to 50. Higher scores indicate greater use of the emotional regulation strategy. Data from all time points will be used to determine the mean differences in change in emotional regulation scores over all follow-up by randomized treatment.

Irritability will be measured by the Affective Reactivity Index (ARI). The ARI scale contains six symptom items. Respondents rate irritability over the last 3 months. Each item has a three-level response category: 'not true', 'somewhat true', 'certainly true'- scored as '0', '1', '2', respectively, giving a range of possible scores of 0-12. The total scores will be calculated and used in this study. Data from all time points will be used to determine the mean differences in change in irritability scores over all follow-up by randomized treatment.