Associations of dietary protein and amino acid intakes with disability-adjusted life years for Alzheimer's disease in Japanese people

Background The number of patients with dementia is increasing worldwide. In Japan, dementia is the most significant reason recognized for people requiring nursing care. Protein is one of the possible preventive nutrients for dementia; however, adequate intake levels can differ according to usual protein intakes and protein sources. Objective This study examined the relationships between disability-adjusted life years (DALYs) for Alzheimer's disease and protein or amino acid intakes. Methods Global Burden of Disease Study data (DALYs for each sex and age group in each year) and de-identified individual records from the National Health and Nutrition Survey Japan (data from 46,831 subjects) from 2001 to 2019 were used. Multiple regression analyses were conducted to assess the relationships between DALYs and protein or amino acid intakes with lifestyle factors and sociodemographic index as confounding factors. Results Higher protein-to-energy ratios were correlated with lower DALYs in women in their 70 s (partial regression coefficient [Coeff.] = −349.488, p = 0.034), in men in their 60 s (Coeff. = −51.484), and in both sexes combined in their 60 s (Coeff. = −26.696, p = 0.015) even after adjusting for other possible nutrient intakes. Additionally, elevated isoleucine, lysine, tyrosine, histidine, arginine, alanine, asparagine, and glycine levels were correlated with lower DALYs in women in their 70 s (Coeff. = −2.752 to −0.141). Conclusions Adequate protein and specific amino acid intakes may be associated with DALYs for Alzheimer's disease.