Exploratory Effects of a Bovine Colostrum-Based Supplement on Salivary sIgA, Leukocyte Profiles, and Health Status in Middle-Aged and Older Adults

Objective: The rapid aging of the population is becoming a serious public health issue. This study aimed to evaluate the effects of a bovine colostrum (BC)-based multi-nutrient supplement on secretory immunoglobulin A (sIgA) levels and health status in middle-aged and older adults. Methods: A total of 188 participants aged 50–85 years were enrolled in a 90-day, double-anonymized trial and randomized to an intervention group or a positive control group. The intervention group received 1.12 g of BC powder daily, containing ≥1 × 10⁸ CFU/g of Bifidobacterium animalis subsp. lactis Bb-12, while the positive control group received regular milk powder. The primary outcome was the change in salivary sIgA concentration. Results: A total of 171 participants completed the trial. After the intervention, the sIgA concentration was notably increased in both groups (p < 0.01). The sIgA concentration was increased from 66.3 (43.9, 113) μg/mL to 77.8 (51.5, 137) μg/mL in the intervention group and from 77.8 (48.8, 115) μg/mL to 85.5 (53.3, 133) μg/mL in the control group, with no significant difference between the two groups after intervention. Among participants aged ≥65 years, the intervention group had a greater increase in the sIgA concentration (p = 0.020). Additionally, the intervention group had lower leukocyte and neutrophil counts and a significantly lower incidence of oral ulcers, fatigue, and the common cold (p < 0.05). Sleep quality improved in both groups (p < 0.05). Conclusion: In the overall study population, no significant between-group difference was observed in the primary outcome (salivary sIgA); therefore, these findings should be interpreted as exploratory. However, potential signals of benefit were observed in older participants (≥65 years), which warrant confirmation in future studies. ChiCTR-ID: ChiCTR2400079567 (https://www.chictr.org.cn/showproj.html?proj=198323).