Dietary B-complex vitamins and sleep quality in relation to cognitive impairment among older adults: non-linear associations and evidence of additive interaction

Meihui Zhang^1,2Yuxuan Wang^1,2Yinghuan Zhang^1,2Quyige Gao^1,2Ying Wang^2*Fan Hu^2*Yong Cai^2,3*

• ¹Shanghai Jiao Tong University School of Public Health, Shanghai, China
• ²Tongren Hospital of Shanghai Jiao Tong University School of Medicine, Shanghai, China
• ³Shanghai Jiao Tong University China Hospital Development Institute, Shanghai, China

Background: Global dementia cases are projected to reach 152.8 million by 2050, with China accounting for approximately 25% of cases. While B-complex vitamins and sleep quality are established modifiable determinants of cognitive health, their potential synergistic effects on cognitive function remain unexplored, particularly in rapidly aging populations. Methods: In this population-based cross-sectional study, we analysed baseline data from 8,806 adults aged ≥65 years in the Shanghai Aging and Retirement Evaluation Survey (January-May 2024). Dietary B-complex vitamins intake was assessed using a validated Food Frequency Questionnaire. Sleep quality was evaluated using the Pittsburgh Sleep Quality Index (PSQI). Cognitive function was measured using the Mini-Mental State Examination, with scores ≤24 indicating cognitive impairment. We examined non-linear relationships using restricted cubic splines analysis and assessed independent associations using multivariate logistic regression. Both multiplicative and additive interactions were evaluated using cross-product terms and three additive interaction indices. Findings: Among 8,806 participants, 677 (7.69%) had cognitive impairment. Higher intake of vitamin B6, B12, and folate showed L-shaped associations with reduced cognitive impairment risk, while PSQI scores demonstrated J-shaped relationships. Compared with lowest quartiles, participants in highest quartiles of vitamin B6, B12, and folate intake had lower odds of cognitive impairment (adjusted OR 0.33 [95% CI 0.25-0.43], 0.43 [0.33-0.55], and 0.33 [0.25-0.43], respectively; all p<0.001), while those with highest PSQI scores had increased odds (2.94 [2.34-3.69]; p<0.001). Significant additive interactions between low B-complex vitamins intake and poor sleep quality were observed (Relative Excess Risk Due to Interaction 0.97 [0.48-1.46]; Attributable Proportion 0.22 [0.10-0.35]; Synergy Index 1.41 [1.14-1.67]; all p<0.001), suggesting a synergistic association with cognitive impairment risk. Interpretation: Our findings reveal a synergistic association of adequate B-complex vitamins intake and good sleep quality with a lower prevalence of cognitive impairment in older adults, suggesting that integrated interventions targeting both nutritional and sleep factors might be more effective than single-domain approaches in preserving cognitive health during aging.