Joint associations of sitting time and depressive symptoms with all-cause and heart disease mortality among adults with diabetes or prediabetes

Depressive symptoms and prolonged sitting are each associated with adverse health outcomes, but their independent and joint associations with mortality among adults with diabetes or prediabetes remain incompletely characterized. We conducted a secondary analysis of six National Health and Nutrition Examination Survey cycles (2007–2018) linked to mortality through December 31, 2019. The analytic sample included 7,333 adults with diabetes or prediabetes. Depressive symptoms were defined as a Patient Health Questionnaire − 9 (PHQ-9) score ≥ 10, and daily sitting time was categorized as < 6 or ≥ 6 h/day. Four joint-exposure patterns were defined: PHQ-9 < 10 and sitting < 6 h/day (Pattern 1); PHQ-9 ≥ 10 and sitting < 6 h/day (Pattern 2); PHQ-9 < 10 and sitting ≥ 6 h/day (Pattern 3); and PHQ-9 ≥ 10 and sitting ≥ 6 h/day (Pattern 4). Survey-weighted Cox models estimated hazard ratios (HRs) for all-cause and heart disease mortality. The sample comprised 5,141 participants with diabetes and 2,192 with prediabetes; 1,197 all-cause and 326 heart disease deaths occurred. In fully adjusted models, PHQ-9 ≥ 10 was associated with all-cause mortality (HR 1.33, 95% CI 1.06–1.67) and heart disease mortality (HR 1.62, 95% CI 1.06–2.48). Sitting ≥ 6 h/day was also associated with all-cause mortality (HR 1.45, 95% CI 1.25–1.69) and heart disease mortality (HR 1.57, 95% CI 1.27–1.95). Relative to Pattern 1, Pattern 4 had the largest estimates for all-cause mortality (HR 1.88, 95% CI 1.44–2.46) and heart disease mortality (HR 2.46, 95% CI 1.57–3.85). Multiplicative and additive interaction analyses did not provide evidence of statistical interaction. Depressive symptoms and sitting ≥ 6 h/day were independently associated with higher all-cause and heart disease mortality, and participants with both exposures had the highest relative hazards. The absence of statistical interaction does not support interpreting sitting time as a modifier of the association between depressive symptoms and mortality. These observational findings warrant confirmation in prospective and intervention studies.