Participants underwent blood tests to measure serum 25-hydroxyvitamin D levels, along with detailed cognitive and depression assessments using standardized screening tools. Further analysis found that lower vitamin D levels were linked to worse depression scores, poorer cognitive performance, and higher blood sugar levels measured by HbA1c. Even after adjusting for age, education, diabetes duration, and other medical conditions, lower vitamin D remained independently associated with having both depressive symptoms and mild cognitive impairment. According to the researchers, every 1 ng/mL increase in vitamin D was associated with about a 23% lower likelihood of having both conditions. Vitamin D levels and other factors associated with depressive symptoms and cognitive impairment in the oldest-old patients with diabetes.