Joint Effects of Physical Activity and Diet Quality on Depression and Mortality in Diabetes

Joint Effects of Physical Activity and Diet Quality on Depression and Mortality in U.S. Adults With Diabetes: A Population-Based Cohort Study Using NHANES 2007-2018 With Mediation and Machine Learning Analyses

This observational study aims to investigate whether physical activity (PA) and diet quality (DQ) can reduce depression and mortality risk in individuals with diabetes. Participants will be adults diagnosed with diabetes during the 2007-2018 cycle of the National Health and Nutrition Examination Survey (NHANES). The main questions to be answered include:

Does higher levels of physical activity significantly reduce the risk of depression in individuals with diabetes? Is higher diet quality associated with lower mortality in individuals with diabetes? Investigators will compare individuals with varying levels of PA and DQ to examine whether these two lifestyle factors, both individually and in combination, have protective effects on mental health and survival.

Participants will:

Complete questionnaires regarding their physical activity and dietary intake; Be assessed for depressive symptoms (PHQ-9); Be enrolled in long-term mortality follow-up (from the National Death Index); Analyses will be categorized according to their PA (measured in MET-min/week) and HEI-2015 dietary score.

Inclusion Criteria:

• Adults aged 20 years and older.
• Diagnosed with diabetes mellitus, defined by self-report, fasting plasma glucose ≥126 mg/dL, or HbA1c ≥6.5%.
• Available data on physical activity, diet quality (HEI-2015), and depression status (PHQ-9).
• Complete demographic and mortality follow-up data.

Exclusion Criteria:

• Missing key exposure or outcome data (e.g., physical activity, HEI-2015, PHQ-9, mortality).
• Pregnant individuals at the time of the survey.
• Participants with unreliable or extreme dietary intake data (e.g., energy intake <500 or >5000 kcal/day).