Colostrum from cows has long been added to various foods in places including Britain, India, Turkey and Scandinavia. Lately, demand has soared. An American retail-analytics firm, SPINS, noted in March that annual sales of colostrum supplements, sold as liquid, powder and capsules, had risen by 155% in the previous year. Enthusiasts claim the “liquid gold” reduces inflammation, aids digestion and immune function. It strengthens muscles, they add, boosts aerobic capacity and rejuvenates skin.

The science is mixed. Start with the immune response. In trials in Poland with 28 swimmers and triathletes, intervention groups were given 25 grams of bovine colostrum—a high dose—every day for 12 weeks. The researchers measured a modest but “favourable” increase in salivary immunoglobulin A, a mucosal antibody that binds to and neutralises bacteria, toxins and viruses. This seems to curb upper-respiratory illness, according to a review of five randomised controlled trials with a total of 152 exercising participants. Writing in 2016 in BMC Sports Science, Medicine and Rehabilitation, the authors found that colostrum reduced episodes of such sickness by 38%. Recovery was also faster.

Those studies, however, were limited to athletes exercising intensely enough to have weakened their immune systems. The trials were also small. And other studies have found colostrum to provide little or no improvement in immune response, even with large doses.

The evidence on gut health is stronger. In a trial in Uganda involving 84 adults with chronic diarrhoea associated with HIV, half were given, in addition to standard therapy, a colostrum supplement. Their diarrhoea tapered off much sooner. After nine weeks, patients in the intervention group had also, on average, increased their body weight by 11%. Participants given standard therapy, but not colostrum, had not recovered weight, the researchers reported in 2011 in the Indian Journal of Gastroenterology.

Such results are attributed to colostrum’s antibodies and antimicrobial proteins such as lactoferrin and lactoperoxidase. These appear to better seal the intestinal lining, reducing “leaky gut” in which inflammatory germ fragments pass into the bloodstream.

By reducing inflammation, colostrum also seems to boost aerobic capacity. And it probably helps that lactoferrin, by binding to iron in the blood, helps blood cells to deliver oxygen. A small trial published in April in the European Journal of Sport Science (EJSS) found that athletes who took 25 grams of colostrum per day for 12 weeks had higher oxygen uptake than those on a placebo.

Such findings are encouraging, but boosters have taken some claims too far. The Ejss study, for example, found no gain in muscle mass. As for skin, no peer-reviewed trials of ingested colostrum’s purported benefits have been published. With the picture thus mixed, colostrum’s cost shouldn’t be an afterthought. Just three or so grams a day can add up to more than $60 a month. ■