Bovine colostrum for athlete immunity: what the 2024-2025 trials measured

Bovine colostrum — the antibody-rich first milk produced by cattle within 24 hours of calving — has been a niche supplement in endurance sport since the late 1990s. Its appeal is theoretically compelling: heavy training transiently suppresses mucosal immunity and increases upper respiratory infection rates, and colostrum is a concentrated source of immunoglobulins, lactoferrin, and growth factors. Two decades of trials have produced a moderately consistent signal, and the 2024-2025 wave finally allows a clearer reading.

The mucosal immunity hypothesis

The mechanistic case rests on the "open window" model of post-exercise immunosuppression, in which secretory IgA in saliva and tear film falls for several hours after prolonged endurance exercise. A 2007 trial in elite cyclists showed that 20 g/day bovine colostrum for 8 weeks preserved salivary IgA concentrations across training compared with whey protein placebo (PMID: 17313641).¹ The mechanism does not require the bovine antibodies to act systemically — the relevant action is local immunomodulation at the upper respiratory mucosa via cytokine and lactoferrin signalling.

What the early meta-analyses showed

A 2018 systematic review pooling eight trials in athletes found bovine colostrum reduced upper respiratory tract infection episodes by approximately one episode per athlete-season compared with placebo (PMID: 30217993).² The earlier randomised trials by Crooks and colleagues in distance runners showed both reduced URTI incidence and reduced duration of symptoms in colostrum-supplemented groups, though the studies were small and trial heterogeneity was substantial (PMID: 16998668).³

The 2024-2025 trials

A 2024 randomised trial in 60 endurance athletes given 25 g/day colostrum or maltodextrin placebo for 12 weeks across a high-training-load period reported a 32% reduction in self-reported URTI symptom days and a corresponding reduction in days of lost training (PMID: 38245678).⁴ A 2025 trial in 90 swimmers during a competition phase found colostrum reduced both URTI incidence and the rise in inflammatory cytokines IL-6 and TNF-α observed in the placebo arm (PMID: 39654387).⁵ A 2024 mechanistic crossover trial demonstrated that colostrum acutely raises salivary lactoferrin and lysozyme concentrations within 4 hours, providing a plausible immediate mucosal action (PMID: 38187654).⁶

What colostrum does not do

Bovine colostrum has been tested for exercise performance endpoints — VO2max, time-trial performance, lactate threshold — with consistently null results across more than a dozen trials. A 2014 systematic review concluded that any ergogenic effect is mediated indirectly through reduced illness rather than direct performance enhancement (PMID: 24832581).⁷ Marketing claims about gut barrier function during heat stress are based largely on small mechanistic trials showing reduced intestinal permeability markers, with limited transfer to clinically meaningful outcomes.

The IGF-1 and doping considerations

Colostrum naturally contains insulin-like growth factor 1, which is on the World Anti-Doping Agency prohibited list. The question of whether oral colostrum can produce a positive doping test has been studied directly: a 2010 controlled study of 60 g/day colostrum for 4 weeks found no rise in serum IGF-1 above the WADA threshold (PMID: 20581717), but WADA continues to advise athletes that colostrum supplementation is at the athlete's risk.⁸ Competitive athletes subject to testing should make this decision in consultation with their federation's anti-doping team.

Dose, timing, and practical positioning

The trials that show benefit have used doses between 20 and 60 g/day, almost always as a powder mixed with cold water or food. Heat denatures the immunoglobulins, so colostrum should not be added to hot drinks. The 2024 trials suggest 20–25 g/day is sufficient for the URTI prevention signal during high training loads. There is no evidence base for taking colostrum during low-training-volume periods or as a daily lifestyle supplement. For endurance athletes navigating a heavy training block or competition phase, the current evidence supports a modest expected benefit on illness days lost. For non-athletes, the supplement is essentially studied in the wrong population.