The essential amino acid L-tryptophan (Trp) appears to play an important role in aging by acting as a general regulator of protein homeostasis. The major route of Trp degradation, the kynurenine pathway (KP), produces a range of biologically active metabolites that can impact or be impacted by a variety of body systems, including the endocrine, haemopoietic, immune, intermediary metabolism and neuronal systems, with the end product of the KP, NAD⁺, being essential for vital cellular processes. An account of the pathway, its regulation and functions is presented in relation to body systems with a summary of previous studies of the impact of aging on the pathway enzymes and metabolites. A low-grade inflammatory environment characterized by elevation of cytokines and other immune modulators and consequent disturbances in KP activity develops with aging. The multifactorial nature of the aging process necessitates assessment of factors determining the progression of this mild dysfunction to age-related diseases and developing strategies aimed at arresting and reversing this progression.

必需氨基酸L-色氨酸（Trp）通过充当蛋白质稳态的一般调节剂，似乎在衰老中起重要作用。Trp降解的主要途径是犬尿氨酸途径（KP），它会产生一系列具有生物活性的代谢产物，这些代谢产物会影响或受到各种身体系统的影响，包括内分泌，造血，免疫，中间代谢和神经系统。 KP的最终产品NAD ⁺，对于重要的细胞过程至关重要。介绍了与人体系统有关的途径，其调节和功能，并概述了衰老对途径酶和代谢产物的影响的先前研究。随着年龄的增长，会出现以细胞因子和其他免疫调节剂升高为特征的低度炎症环境，继而导致KP活性受到干扰。衰老过程的多因素性质需要评估决定这种轻度功能障碍向年龄相关疾病进展的因素，并制定旨在阻止和逆转这种进展的策略。