In plain terms: Bovine Colostrum shows early signals in human research but the evidence is limited -- small trials, surrogate endpoints, or not yet independently replicated. It is an emerging area, not yet a proven one.
Bovine Colostrum
The evidence as the record states it
Hajihashemi et al. (Dig Dis Sci, 2024; PMID 38361147): meta-analysis of 10 trials in healthy athletes and patients mixed; the urinary lactulose/rhamnose ratio fell (mean difference -0.24) with extreme heterogeneity (I2 99 percent), the lactulose/mannitol ratio fell marginally (-0.01), and plasma I-FABP did not differ. Against: Buckley et al. (Nutrients, 2009; PMID 22253980), 30 men running three times a week for 8 weeks on 60 g/day colostrum, whey or control; the lactulose/rhamnose ratio ROSE on colostrum (251 percent) versus whey (21 percent) and control. Morrison et al. (Appl Physiol Nutr Metab, 2014; PMID 25068884), 15 men, 1.7 g/kg/day for 7 days, exercise in the heat: no effect on permeability, physiology or performance. Immune measures: Główka et al. (Nutrients, 2020; PMID 32276466), meta-analysis of 10 trials, 239 athletes, no or very small effect on serum and saliva immunoglobulins, lymphocytes or neutrophils. Self-reported upper respiratory symptoms: Jones et al. (BMC Sports Sci Med Rehabil, 2016; PMID 27462401), 5 trials, 152 exercising adults, symptom days 44 percent fewer over 8 to 12 weeks, risk of bias moderate to high; a self-report endpoint, shown as context. Grade C: pooled randomized evidence on surrogate markers that disagrees with itself and with the one training trial that measured the opposite effect.
Why Grade C and not Grade B
Grade C reflects early or limited human evidence -- small trials, surrogate endpoints, or preliminary findings not yet independently replicated. The evidence points in a promising direction but does not yet meet the standard for Grade B. A single well-powered, independently replicated trial with a meaningful endpoint would move this to Grade B or higher.
What would move this grade
A well-powered randomized trial with an objective, clinically meaningful primary endpoint and at least one independent replication would support Grade B or higher.