Background <p>Homocysteine levels are closely associated with overall health. An elevation in homocysteine can lead to a variety of health issues and is influenced by vitamins B12, B6, and folic acid. However, the dose-response relationship between homocysteine and vitamin A remains unclear among the middle-aged and elderly population in rural China.</p> Objective <p>This study investigates the dose-response relationship and threshold effect between serum homocysteine and vitamin A levels in vivo. Utilizing large-scale data from middle-aged and elderly individuals in China, it also evaluates these relationships across gender and age subgroups, providing a scientific basis for preventing and treating hyperhomocysteinemia in this population.</p> Methods <p>To examine the dose-response relationship between vitamin A and homocysteine, we used multiple linear regression, multinomial logistic regression, generalized additive models, and restricted cubic splines. This analysis involved 28,860 middle-aged to elderly participants from rural China.</p> Result <p>The distribution of vitamin A and homocysteine levels is similar across different genders and age groups. However, homocysteine levels are elevated in men and individuals over the age of 65. A U-shaped dose-response relationship exists between these two variables, independent of gender or age. In China, the vitamin A levels among middle-aged and elderly populations are categorized into quintiles. As the concentration of vitamin A increases, the β coefficient exhibits a trend that initially decreases before subsequently increasing.The serum levels of both vitamin A and homocysteine across various genders and age groups demonstrate a U-shaped relationship. Specifically, as serum vitamin A levels rise, homocysteine levels first decline before rising again. This U-shaped nonlinear association between vitamin A and homocysteine was also identified within the high-homocysteine group. Restricted spline analysis revealed that with increasing serum vitamin A concentrations, the odds ratio (OR) for hyperhomocysteinemia initially decreased before increasing.Notably, when serum vitamin A concentration reaches 0.514&#xa0;µg/ml, the OR for hyperhomocysteinemia exceeds 1.</p> Conclusion <p>This study found a U-shaped relationship between serum vitamin A and homocysteine levels in middle-aged and elderly Chinese people. Proper vitamin A levels may help reduce homocysteine in those with hyperhomocysteinemia. The research provides a scientific basis for understanding this correlation and supports precise prevention and management of hyperhomocysteinemia.</p>