The association between animal‑based and plant‑based protein intake with sleep quality, mood, anxiety, depression and stress among elderly: a cross-sectional study

Abstract

Background: Dietary protein intake may influence sleep quality, mood, anxiety, depression, and stress in older adults, but evidence is limited. This study examined the impact of protein source (animal vs. plant) and quantity on these outcomes in the elderly. Methods: In this cross‑sectional study, 396 Iranian adults aged 65–85 years with sleep or mental health challenges were recruited from hospitals and clinics. Dietary intake was assessed using a validated 168‑item Food Frequency Questionnaire. Psychological health was measured with the Depression, Anxiety, and Stress Scale (DASS‑21), sleep quality with the Pittsburgh Sleep Quality Index (PSQI), and mood with the Profile of Mood States (POMS). Results: After adjustment for covariates, higher total protein intake was marginally associated with better sleep quality (OR = 0.32, 95 CI: 0.11–0.96) and showed a non‑significant trend toward improved mood (OR = 0.42, 95 CI: 0.14–1.27). Interactions were observed with COVID‑19 history, smoking, and gender. For example, individuals with high protein intake and prior COVID‑19 infection had lower odds of depression (OR = 0.32, 95 CI: 0.13–0.76) and a non‑significant trend toward lower stress. Men with high protein intake had lower odds of poor sleep quality (OR = 0.19, 95 CI: 0.07–0.53) and anxiety (OR = 0.39, 95 CI: 0.18–0.84). Higher plant protein intake was associated with increased odds of poor sleep quality (OR = 2.73, 95 CI: 1.36–5.49). Animal protein intake was marginally linked to poorer sleep (OR = 1.08, 95 CI: 0.51–2.29) but associated with reduced odds of poor mood (OR = 0.24, 95 CI: 0.10–0.57) and depression (OR = 0.39, 95 CI: 0.18–0.85). No significant associations were found between total protein intake and depression, anxiety, or stress in fully adjusted models. Conclusion: Higher total protein intake was associated with some improvements in sleep and mood, but findings were inconsistent across outcomes. Animal protein appeared beneficial for mood and depression, whereas both plant and animal protein were linked to poorer sleep quality. These mixed results highlight the complexity of diet–mental health relationships and the need for cautious interpretation. © The Author(s) 2025.