ABSTRACT Even before increased social isolation associated with the COVID-19 pandemic, 43% of adults aged 60 and older reported experiencing loneliness. Depression and loneliness often co-exist and are significant issues faced by middle-aged as well as older adults because each condition is likely to worsen health outcomes. This study of middle-aged and older adults examined how depression and loneliness affect diabetes (DM) control (A1C levels). This study is a secondary analysis of data from the Midlife in the United States Refresher (MIDUS-R) survey, a national survey of adults aged 25–74 years. Correlation analyses were conducted, and a hierarchical logistic regression was estimated to predict A1C levels ≤7% (recommended goal) or >7 using 1) demographics and physical health (ethnicity, gender, education, age, and comorbidities), 2) family and friend support, and 3) depression and loneliness. The sample of 92 participants with DM and A1C data from the MIDUS-R had mean age = 57.37, were 51% male, 68% non-Hispanic White; 39.1% had A1C >7. The average level of depression was low (CES-D mean 9.42) and loneliness was moderate (UCLA scale mean 12.43). Loneliness was correlated with A1C (r= .26, p< .05); depressive symptoms (r= .71, p< .001), family and friends support (r= −.36, r= −.38, respectively, both p< .001). Only loneliness significantly predicted higher A1C levels. People with higher levels of loneliness had increased odds of having A1C >7 (OR = 1.18, p < .05) after controlling for depression and all other variables. Loneliness had a greater impact than depression on A1C level among persons with DM. Healthcare providers should assess patients for loneliness as well as depression and reduce adverse health impacts by referring to psychosocial support as needed.