4. Discussion
sleepiness, sleep complaints, fatigue
HEART
We investigated whether LcS affects the daytime performance of healthy office workers with sleep complaints and observed that LcS intake suppresses the decline in perceived attention in the afternoon. This result is considered to be supported by the fact that other VAS items (sleepiness, fatigue, motivation, and optimism) tended to be better during the LcS intake period. All items of VAS were lower in the afternoon than in the morning, suggesting an overall decline in performance in the afternoon. The VAS score of attention in the afternoon was significantly higher during the LcS intake period than during the placebo intake period. The VAS attention score in the afternoon during the LcS intake period was similar to that of the placebo intake period in the morning, indicating that the effect size of LcS was comparable to the range of diurnal variation.During the LcS intake period, the EEG theta power that appeared during the resting state (eyes open) and when performing tasks in the afternoon was significantly lower than that during the placebo intake period. Correlation analysis showed that the changes in daytime attention with LcS intervention were associated with the changes in theta power in the resting state (eyes closed) in the afternoon (The shortened latency of the ERP P300 also supports the results, indicating improved perceived attention. ERP P300 latency is believed to indicate the attentional state of the brain. Prolonged P300 latency is related to aging [Heart rate during the LcS intake period was lower than that during the placebo intake period, regardless of the time of day or if the individual was resting/performing a task, with a significant difference in the resting heart rate (with eyes closed) in the morning. Moreover, changes in heart rate with closed eyes in the morning were correlated with improved mood (positively for the KSS, negatively for motivation and optimism). A reduction in heart rate induced by LcS intervention has also been observed after the intake of a hot water extract of LcS [Only individuals with sleep complaints were included in this study, and stress was not taken into consideration. The stress levels of the participants enrolled in this study were not very high in terms of JPSS values. LcS has been shown to prevent the worsening of stress and sleep quality under academic stress [The present study must be seen as an exploratory study in this field, and thus, no formal sample size calculation was performed. We set the sample size to 12, considering the handling capability of the EEG system, but this may be insufficient for making strong conclusions. To eliminate this limitation, we adopted a crossover study design. The crossover design has high power and statistical efficiency, and it is possible to obtain an estimate with the same level of accuracy as a parallel design, even with a smaller number of participants [