Triglyceride Level- and MTHFR- Specific Mediation Effect of Handgrip Strength on the Association of Dietary Protein Intake and Cognitive Function in the Chinese Elderly

Background: Recent findings suggest that both dietary protein intake and hand grip strength (HGS) were associated with cognitive function, however, few studies have been devoted specifically to the mediation effect of HGS on the association of dietary protein with cognitive function. Objectives: To confirm the hypothesis that HGS mediated the association of dietary protein intake with cognitive function in the elderly, which was modified by triglyceride level and methylenetetrahydrofolate reductase (MTHFR) gene status. Methods: This cross-sectional study included 3,268 participants. Dietary protein intake, HGS, and cognitive function were collected by food frequency questionnaires (FFQ), grip measurements and mini mental state examination (MMSE), respectively. In this mediation analysis, dietary protein intake was entered as independent variable, HGS was entered as mediator, and cognitive function was entered as dependent variable. Results: HGS significantly mediated the associations of dietary protein (β = 0.0013, 95% CI: 0.0007, 0.0022), animal protein (β = 0.0024, 95% CI: 0.0012, 0.0037), and plant protein intake (β = 0.0011, 95% CI: 0.0001, 0.0023) with cognitive function in total participants, with the mediated proportion of 16.19%, 12.45% and 20.57%, respectively. Furthermore, significant mediation effects of HGS on the associations of dietary protein, animal protein, and plant protein intake with MMSE score were found in the elderly without hypertriglyceridemia or in MTHFR C677T CC/CT carriers. Conclusion: This study suggested that HGS mediated the association of dietary protein intake with cognitive function, and this mediation effect was modified by triglyceride level and MTHFR C677T gene status.