Effects of intake of Lactobacillus casei subsp. casei 327 on skin conditions: a randomized, double-blind, placebo-controlled, parallel-group study in women

Abstract

Lactic acid bacteria are gut flora that play key roles in intestinal homeostasis, which may affect a variety of physiological functions. Our preliminary double-blind, placebo-controlled, parallel-group trials have suggested that intake of heat-killed Lactobacillus casei subsp. casei 327 (designated L. K-1) is effective for improving skin conditions. The aim of this study was to confirm the effect of L. K-1 intake in a randomized, double-blind, placebo-controlled, parallel-group study in healthy female volunteers. Sixty-four subjects were allocated to either the placebo food group (group P, n=32) or active food group (group A, n=32), in which subjects consumed lactobacillus K-1 50 mg (approximately 1 × 10¹¹ bacteria) daily for 8 weeks. After excluding subjects who declined to participate (n=1), violated restrictions (n=4), or were judged ineligible by the principal investigators (n=1), data obtained with 58 subjects (30 in group A and 28 in group P) were analyzed for efficacy by comparing differences from pretrial levels between the two groups. When the level of transepidermal water loss (TEWL) was measured at the arm, the level of TEWL at week 4 of the intake period was significantly lower in group A than group P (p=0.021), suggesting an improvement of skin barrier function. Analysis of skin condition questionnaire data revealed a significant reduction in skin flakiness on the face (week 4). No adverse events were associated with intake of the test foods. The safety of L. K-1 was also confirmed in an independent open-label trial in 11 healthy subjects who consumed excessive amounts of L. K-1 250 mg (approximately 5 × 10¹¹ bacteria). Intake of L. K-1 may therefore be beneficial to skin condition improvement.

Keywords: Lactobacillus casei; clinical study; lactic acid bacteria; skin conditions; transepidermal water loss.

Fig. 1.

Outline of the study. Subjects in group A consumed L. K-1-containing tablets, and subjects in group P consumed placebo tablets. Exclusion before randomization due to judgment by the investigator (n=9) was mainly based on age, stool frequency, or TEWL value.

Fig. 2.

Time course of the effect of L. K-1 intake on TEWL and stratum corneum hydration at the cheek and arm. The changes from pretrial values in TEWL (ΔTEWL) at the right cheek (A) and left upper arm (B) and in corneum hydration (Δcorneum hydration) at the right cheek (C) and left upper arm (D) are shown. Each value is expressed as the mean ± SD. p values were calculated between groups using the unpaired Student’s t-test.