Eligible participants were generally healthy adults who met all the inclusion criteria and none of the exclusion criteria. Before enrollment, all the candidates received a sufficient explanation of the study and provided written informed consent.

Inclusion criteria:

1) Healthy Japanese men or women aged 20 to 79 years old at consent; 2) individuals with a tendency toward frequent urination and self-perceived sleep disturbance; 3) individuals with the capacity to consent who received an adequate explanation of the study’s objectives and content, voluntarily agreed to participate, and provided written informed consent.

Exclusion criteria:

1) Individuals receiving outpatient care at the time or with a current medical history of diseases that could have affected this study; 2) Individuals suspected of overactive bladder according to the Overactive Bladder Symptom Score (OABSS): urgency score (Question 3) > 2 and total OABSS ≥ 3; 3) Individuals suspected of benign prostatic hyperplasia; 4) Individuals with gastrointestinal diseases or a surgical history that could affect digestion and absorption; 5) Individuals regularly using medications that could have influenced the study; 6) Individuals unable to discontinue the use of drugs, supplements, or health foods related to urination or sleep; 7) Individuals engaged in night shifts, rotating shifts, or heavy labor; 8) Individuals with a current or past history of drug or alcohol dependence; 9) Individuals who were pregnant, breastfeeding, or intended to become pregnant during the study; 10) Individuals living with a care-dependent person or caring for an infant; 11) Individuals with allergies to components of the study foods; 12) Individuals who were at the time participating in or intending to participate in other clinical studies that could have affected this study at baseline; 13) Individuals deemed unsuitable by the principal investigator for other reasons.

The study protocol was registered in the clinical trial registry operated by the University Hospital Medical Information Network Research Center (UMIN-CTR) under ID UMIN000053746 (trial title: A Study to Evaluate the Effects of a Plant Ex-tract-containing Food on Sleep Complaints: A Randomized, Double-blind, Placebo-controlled, Parallel-group Trial).

This was a 9-week, randomized, double-blind, placebo-controlled, parallel-group trial (allocation ratio, 1:1), consisting of a 1-week pre-observation period followed by an 8-week intake period. No methodological changes were made after the study’s initiation.

Paid volunteers were recruited. The principal investigator enrolled participants according to the inclusion and exclusion criteria. A statistician performed block randomization with adjustment for age and sex, allocating the participants to two groups. An allocation officer not directly involved in the trial allocated them to an active group and placebo group. This officer prepared and sealed a key-code table and kept it sealed until the analysis population had been finalized, to maintain blinding for all except the allocation officer. The study foods were dispensed in plain aluminum pouches containing 8-week tablets at the daily dose to ensure blinding of the participants and implementers.

The participants were instructed throughout the study to maintain their usual lifestyle (in terms of diet, alcohol consumption, exercise, bedtime, and smoking); refrain from using drugs, supplements, and health foods (including Foods for Specified Health Uses and Foods with Function Claims) that might have affected the study; and avoid binge eating/drinking or staying up late. If medication was unavoidably required due to illness, the participants were to consult the study site in advance.

A prior placebo-controlled study in healthy Japanese adults reported a significant reduction in nocturnal awakening time with Epilobium angustifolium extract intake compared with placebo [7] . Based on these data, a sample size calculation for the present study (two-sided α = 0.05; power = 0.80) yielded 20 participants per group. Allowing for attrition, the target enrollment was set at 25 per group (total n = 50).

During the intake period, the participants consumed the assigned study food. The active food was a compressed tablet containing Epilobium angustifolium extract, along with reduced maltose syrup, cellulose, calcium stearate, and silicon dioxide. The placebo matched the active food in appearance; the Epilobium angustifolium extract was replaced with caramel coloring, and the quantities of reduced maltose syrup, calcium stearate, and silicon dioxide were adjusted. The daily intake for both the active and placebo foods was one tablet (250 mg) once daily with cold or lukewarm water.

The nutritional compositions of the tablets are presented in Table 1 . The active food provided 15 mg/day of oenothein B derived from Epilobium angustifolium extract.

^aCalorie conversion factors: protein, 4; fat, 9; and carbohydrate, 4; ^bNitrogen protein conversion factor: 6.25.

The primary outcome was the N-QOL score, assessed at baseline, and 4 and 8 weeks of intake. The N-QOL comprises 13 items: 6 items for Sleep/Energy, 6 for Bother/Concern, and 1 for Overall Health Perception. For the first 12 items, lower raw scores indicate better QOL and range from 0 (highest QOL) to 4 (lowest QOL). For analysis, these 12 items were reverse-scored so that higher scores indicate better QOL, ranging from 0 (lowest QOL) to 4 (highest QOL). Overall Health Perception is rated from 0 (not at all) to 10 (very much), with higher scores indicating better QOL. The scores are presented as the Total Score (the sum of the 12 items excluding the last item); the two subscales of Sleep/Energy (the sum of 6 items) and Bother/Concern (the sum of 6 items); and the single-item Overall Health Perception [4] .

The two subscales were scaled to a 0 - 100 metric as follows (with one Bother/Concern item treated as missing if the response “no family/household members” was given to the item concerning annoyance to family/housemates):

$\text{Subscale total score}=\left(\text{sum of item scores for the subscale}/\text{24}\right)\times 100$

The total score was scaled to 0 - 100 as follows [4] :

If all 12 items were answered:

$\text{N-QOL total score}=\left(\text{sum of the 12 item scores}/\text{48}\right)\times 100$

If 1 item was missing (11 items answered):

$\text{N-QOL total score}=\left(\text{sum of the 11 item scores}/44\right)\times 100$

No changes were made after the study’s initiation.

The participants were provided with a food diary and a participant log and instructed to record the following daily from one week before the start of intake through the intake period: 1) Study food intake status; 2) Sleep duration; 3) The use of medications (excluding nutritional drinks but including newly designated quasi-drugs and quasi-drugs within the new scope); 4) The presence of physical changes; 5) Changes in lifestyle and their details; 6) Dietary content (including supplements, health foods, drink products, and alcohol).

At screening, the OABSS was administered to characterize the background related to overactive bladder. A questionnaire survey was conducted to confirm whether participants met the inclusion criteria of “individuals with a tendency toward frequent urination and self-perceived sleep disturbance”.

The analysis population was the per-protocol set (PPS). Repeated-measures ANOVA was used to assess the group-by-time interaction. Between-group comparisons (active vs. placebo) at each time point were conducted using unpaired t-tests on observed values and changes from baseline. All tests were two-sided with a significance level of 5%. Statistical analyses were performed using IBM SPSS Statistics, version 28. The participant characteristics are presented as means ± standard deviations; other data as means ± standard errors. No additional analyses were conducted. If a score was missing during the study, that participant was excluded from analyses of the corresponding score.

A total of 50 participants (29 male, 21 female) were enrolled and randomized; none dropped out before starting the intervention. In total, 25 were allocated to the active group and 25 to the placebo group. During the study, 1 participant in the active group (female) discontinued for reasons unrelated to the study, leaving 49 completers. After study completion, 2 participants met exclusion criteria due to violations of study precautions (1 per group), resulting in 47 participants (28 male, 19 female) in the PPS. The analyses were performed according to the original allocation.

Recruitment through follow-up occurred from February to June 2024. The study concluded after all the participants had completed follow-up. The baseline characteristics are shown in Table 2 , and the CONSORT flow diagram is presented in Figure 1 .

Values are expressed as means ± SDs; No significant difference was observed.

The N-QOL scores are summarized in Table 3 . Significant group-by-time interactions were observed for the N-QOL total score and Sleep/Energy score. In between-group comparisons of changes from baseline at each assessment, the active group showed significantly greater improvements than the placebo group at 4 and 8 weeks. No significant interactions or between-group differences were observed for Bother/Concern or Overall Health Perception.

Values are expressed as means ± Ses; Significantly different from the placebo group (*P < 0.05).

No adverse events attributable to the study food were observed during the trial.