Nutrients 2023 , 15 , 3466
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of LPHEAL9, and they were mild in intensity (a non-pathological increase in alanine aminotransferase levels). Thus, intake of LPHEAL9 was found to be safe and well tolerated. 4. Discussion The present exploratory study was conducted to gain insight into the effect of LPHEAL9 on the gut–brain axis. Measurements of stress, cognition, mood, and sleep were investigated after intake of LPHEAL9 or placebo for 12 weeks. The primary findings in this study indi- cated a positive impact on cognitive performance, especially memory functions, after intake of LPHEAL9 compared to placebo. These results may be connected to the improvements over time seen by LPHEAL9 in sleep quality, overall mood, and awakening cortisol. Perceived stress (PSS) was reduced significantly in both the LPHEAL9 and the placebo groups, with no difference between the groups. Thus, a large placebo effect on subjects with moderate stress was seen. This observation aligns with a study testing L plantarum DR7 in a similar population [9]. However, the administration of L. paracasei Lpc-37 to subjects with chronic stress was found to significantly decrease PSS in the probiotic group compared to the placebo group in another study [18]. Some earlier studies also indicate a significant decrease in stress levels after intake of probiotics in subjects with low stress. Messaouidi et al. [19] observed a significant difference in PSS in a subgroup with the lowest urinary free cortisol levels at baseline after intake of L. helveticus R0052 and B. longum R0175 in comparison to placebo. In an earlier study on LPHEAL9, lower levels of cortisol were seen after the Trier Social Stress Test (TSST) in the LPHEAL9 group compared to the placebo group. These results were even more pronounced in a subgroup that did not have chronic stress on the day of performing the TSST [4]. In the current study, a significant reduction in the awakening cortisol level over time was observed in both groups, while the cortisol level directly after awakening (T0) significantly decreased only in the LPHEAL9 group at week12. The connection between stress and sleep has been known for a long time. One of the causes of this connection is the “fight or flight” response arising from stressful situations. This leads to increased heart rate and blood pressure, as well as increased levels of cortisol and adrenaline, responses that greatly affect sleep quality and duration of sleep [20]. Several studies have investigated the impact of sleep on different lactobacilli strains. A randomized and placebo-controlled study in healthy but stressed students found that intakeof L. plantarum JYLP-326 was able to relieve symptoms of anxiety, depression, and insomnia after three weeks of consumption [21]. Similarly, L. casei Shirota was found to improve sleep quality in terms of sleepiness when rising and sleep length in healthy but stressed adults [22]. However, a probiotic mixture given to 38 healthy volunteers for six weeks did not show a significant difference in sleep between the probiotic and placebo groups measured using PSQI [23]. Like the present study, they did find improvements within the probiotic group in both sleep and mood. In the present study, both groups were found to have significantly improved PSQI, while two of the sub-scores significantly improved only within the LPHEAL9 group. The significantly improved results in overall sleep quality, as well as in daytime dysfunction, may be connected to the significantly decreased immediate awakening cortisol (T0) level found only in the LPHEAL9 group at week 12 compared to baseline. The overall improved sleep in both groups could be connected to the significantly decreased levels of perceived stress, which were similar for both groups over the course of the study. Mood is defined as a transient state of mind, and one of the most common methods used to measure it is the POMS questionnaire. Apart from the overall score obtained from this test, there are six pre-defined sub-scores (Anger–Hostility, Confusion–Bewilderment, Depression–Dejection, Fatigue–Inertia, Tension–Anxiety, Vigor–Activity, and Friendliness). In the current study, all the sub-scores were significantly improved within the LPHEAL9 group from baseline to week 12. The placebo group reported minor but still significant changes within four of the six sub-scores. For three of the sub-scores, there was a trend for a difference in favor of LPHEAL9 compared to placebo, namely Anger–Hostility, Depression–
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