This is a randomized clinical trial (RCT) to determine the effectiveness of vitamin D3 supplementation on depressive symptoms, self-management, and blood pressure in approximately 180 adult women with type 2 diabetes who have significant depressive symptoms. Consenting adult women who are eligible to participate will be randomly assigned to either a weekly dose of 50,000 international units of vitamin D3 supplementation or a matching weekly active comparator of 5,000 international units of vitamin D3 for six months. Participants will complete approximately four in-person study visits and several telephone visits throughout the six month trial period, where the researchers will assess depressive symptoms, diabetes self-management, and systolic blood pressure.

The primary aim of this study is to determine the effect of vitamin D supplementation on depressive symptoms, self-management, and systolic blood pressure compared to placebo. The hypothesis is that women receiving vitamin D supplementation will report fewer depressive symptoms, increased diabetes self- management mediated by depression improvement, and will have a lower systolic blood pressure compared to those taking placebo at three and six months follow-up.

The secondary aim is to explore the mechanistic effect of vitamin D supplementation on inflammatory biomarkers and their association with depression. Here, the hypothesis is that women receiving vitamin D supplementation will have a decrease in inflammatory biomarkers which will be associated with fewer depressive symptoms compared to those taking placebo at three and six months follow-up.

Inclusion Criteria:

• Women age 21 and older
• Objective evidence of depressive symptoms at the screening and baseline visits
• Diagnosis of type 2 diabetes currently being treated by a healthcare provider
• Blood vitamin D level less than 32 nanograms-per-deciliter (32 ng/dl)

Exclusion Criteria:

• Current alcohol or substance use disorder
• Any unstable or severe psychiatric disease including diagnoses of schizophrenia, bipolar affective disorder, dementia, delirium, or other psychotic disorder
• Severe complications of diabetes, such as blindness and/or amputation
• Any malabsorption disorder, such as Crohn's disease and/or celiac sprue
• Elevated serum calcium level deemed significant by the Principal Investigator
• Use of 1,000 or more international units daily vitamin D 60 days before enrollment and unwillingness to discontinue vitamin D supplementation 30 days before enrollment.
• Use of St. John's Wort and unwillingness to discontinue St. John's Wort three weeks prior to enrollment.
• Participants who are pregnant, nursing, or planning to become pregnant during the study.
• Baseline systolic blood pressure (SBP) greater than 160 millimeters of mercury (mmHG) or diastolic blood pressure (DBP) greater than 100 mmHG.
• Other serious medical conditions (e.g., cancer, multiple sclerosis, etc.) deemed clinically significant by the Principal Investigator

The baseline analysis population comprises all patients randomized to high dose or lose dose therapy

Adverse event data were collected for seven months

There are no limitations or caveats to report