The Burden of Obesity and Type 1 Diabetes: Distinct and Synergistic Effects to Worsen Perceived Health and Psychosocial Distress

Background: Type 1 diabetes (T1D) and overweight/obesity (OW) are chronic conditions impairing health-related quality of life (HRQoL). While diabetes primarily affects psychosocial domains, OW impacts physical functioning and social stigma. Despite the increasing prevalence of OW among individuals with T1D, their combined effect on HRQoL has not been investigated. Methods: In this cross-sectional, multicentre study we evaluated HRQoL in 43 people with both T1D and OW (T1DOW), 40 people with T1D normal weight (T1DNW), 58 normal weight people without diabetes (NADNW) and 41 people with OW without diabetes (NADOW). All participants completed generic HRQoL questionnaires (WHO-5, SF-36). People with T1D additionally completed diabetes-specific tools (DDS, DES-SF and T1-DDAS). Adjusted multivariate analyses were used to evaluate the independent and interactive effects of T1D and OW on HRQoL. Results: T1D was associated with reduced well-being (WHO-5, p = 0.003), impaired general health perception (SF-36, p < 0.001) and lower social functioning (SF-36, p = 0.026). OW significantly worsened physical functioning (p < 0.001) and role limitations due to physical health (p = 0.036). Bodily pain was synergistically affected by both T1D (p = 0.043) and OW (p = 0.006), with people affected by both T1D and OW showing the worst score. Overall, T1DOW was associated with greater detrimental effects on WHO-5 and SF-36 outcomes compared to OW and T1D alone. Among people with T1D, OW selectively increased interpersonal distress (DDS, p = 0.020), while empowerment and T1D-specific distress were unaffected. Conclusions: T1D and OW exert distinct, partially overlapping effects on HRQoL. Their coexistence worsens body pain and interpersonal distress and emphasises the need for integrated strategies in managing ‘double diabetes’.