Supplementation with whey peptide rich in β-lactolin improves trait anxiety and subjective stress in healthy adults: a randomized, double-blind, placebo-controlled study

Mental disorders have become one of the most burdensome health concerns. We have previously demonstrated that whey-derived β-lactolin (glycine–thereonine–tryptophan–tyrosine tetrapeptide) activates dopaminergic systems and improves psychiatric function in rodents. However, the effects of β-lactolin on human mood states have not been investigated. This randomized, double-blind, placebo-controlled study aimed to evaluate the effects of supplementation with β-lactolin–rich whey peptide on human mood states. Sixty healthy adults (aged 45–64 years) with relatively low psychological health were randomly allocated to receive either whey peptide (containing β-lactolin 1.6 mg/day) or placebo for 6 weeks. Mood states (primary outcomes) were evaluated using self-reporting questionnaires. Health-related quality of life (QOL), salivary stress marker and lipid mediator levels were evaluated as secondary outcomes. Compared with placebo, supplementation with β-lactolin improved changes in trait anxiety (p = 0.046), as assessed using the state–trait anxiety inventory, and in subjective stress (p = 0.043), as assessed using the Perceived Stress Scale. In the assessment of QOL, changes in the vitality subscale and mental health summary score of the 36-Item Short-Form Health Survey were improved in the β-lactolin group. The levels of salivary immunoglobulin A were significantly higher in the β-lactolin group. In a subgroup analysis by median age (54.5 years), subjective stress and salivary prostaglandin levels were significantly decreased by β-lactolin supplementation in the 45–54 -year-old subgroup. In conclusion, supplementation with β-lactolin improves trait anxiety, subjective stress, and psychological QOL, which may be associated with immunologic responses detected via salivary analysis.