Dietary tryptophan and aging

Abstract

This paper considers findings which may relate to whether there may be a correlation between dietary L-tryptophan and aging. Early studies had reported that animals fed a tryptophan-deficient diet showed increased longevity compared to controls. Although decreased serotonin levels due to the tryptophan-deficient diet was considered of importance for the increased longevity, a more likely explanation was decreased diet intake due to the deficient diet. Indeed, decreased diet consumption as well as decreased energy intake have been shown to lengthen the lifespan of animals. Greater quantitative assessment between the effect of a tryptophan-deficient diet and that of decreased energy intake needs to be obtained. Our recent findings that one mouse strain (NZBWF1), which is autoimmune susceptible and has a relatively short lifespan, demonstrate a significantly decreased binding affinity for L-tryptophan by hepatic nuclei when compared to other mouse strains are of much interest. These results stimulated us to reconsider the issue whether L-tryptophan itself may influence the aging process. Since L-tryptophan has a regulatory effect on hepatic protein synthesis which may be related to its binding to a specific nuclear receptor, much akin to what occurs with certain steroid hormones which are considered to be involved in the aging process, this review explores the possibility that L-tryptophan via its regulatory action may be of great importance and merits further investigation. This indispensible dietary component may have a vital regulatory control in the normal state and possibly also during the process of aging.