6. Limitations
In this study, the relationships between and within the efficacy of dietary supplements, sleep problems, and PCs were explored. We succeeded in identifying the PCs and sleep problems that influence the efficacy of dietary sleep-support supplements. Individual patients should benefit from the use of our criteria to select dietary sleep-support supplements. However, little information is currently available in regard to how individual biological and genetic characteristics affect a supplement’s efficacy. It is therefore possible that more significant PCs will be identified in the future, and these will also be incorporated to personalize supplementation more precisely based on personal life habits, sleep conditions, sleep problems, and biological markers to support the sleep of specific individuals. In parallel, the mechanisms involved in the relationships between and within PCs, sleep problems, and the efficacy of dietary sleep-support supplements should be studied. However, it is not practical to reveal all mechanisms; therefore, to reveal the interesting interactions and mechanisms, in vitro and in vivo studies should be considered. In particular, enhancing supplement efficacy by taking dairy products is a novel approach with broad effects, so it is important to examine its mechanisms to evaluate the benefit and risks of this method.