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

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Bovine colostrum is a concentrated source of immunoglobulins, lactoferrin, and growth factors, which is why endurance athletes have used it since the late 1990s to blunt the dip in mucosal immunity that follows heavy training. 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 systematic review and meta-analysis of 10 randomised trials in athletes and physically active people, however, found that the signal sits mainly on illness outcomes rather than systemic immunity: bovine colostrum had no or only a fairly low effect on circulating and salivary immunoglobulins, lymphocytes, and neutrophils, even though earlier work has shown reduced upper respiratory infections (PMID: 32276466).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.