When Team GB member Zoe Smith was described by a newspaper as being "on a special diet of colostrum", the weightlifter was outraged. "I assure you it's not true," she tweeted. "I'm a normal person who eats normal food and the occasional protein shake. Stop making me sound like a colostrum drinking freak!"

Perhaps Smith's reaction reflects a misplaced distaste for ingesting milk created straight after a cow gives birth, but while she isn't taking bovine colostrum, plenty of other British Olympic athletes will be – and with good reason.

"It's not a wonder food," says Dr Glen Davison, a sports scientist at the University of Kent, "but it can be very useful in boosting the immune system, especially during periods of intense physical training and when someone is under a lot of stress."

Colostrum is produced by all mammals in the first few days after giving birth. This first milk is packed with a huge amount of goodies, including immunoglobulins, anti-microbial peptides and other bioactive molecules including growth factors – a nutritional armoury designed to get a newborn through the critical first few days of life. Its properties have been revered for thousands of years across many cultures: in ancient Chinese medicine it was regarded as a vital health-giving potion, and for the Maasai people of Kenya and Tanzania it has long been regarded as an important part of a healthy diet. In Britain, dairy farmers refer to it as beestings: traditionally, mother cows would be milked after feeding their newborn calves and any surplus colostrum was used to make an extra-creamy, and very healthy, pudding.

Over the past five years it has become an increasingly popular dietary supplement for many athletes. It is converted into a powder, and added to other drinks and shakes. "Most of the commercially available bovine colostrum here comes from organic cows in New Zealand," says Davison. "It's not clear yet what the optimum amount to take per day is, but some studies show benefits from as little as two grams."

Gastroenterologist Professor Raymond Playford of Plymouth University has researched the benefits for athletes of taking colostrum. "When they are in intense periods of training, many athletes develop gut problems – 'runners' trots' – which can have a serious effect on their performance," he says. "They're caused by a combination of stress and by the raising of their body's core temperature by about two degrees, which seems to increase the permeability of the gut wall and that in turn allows toxins into the bloodstream that wouldn't usually be there.

"My studies show that this tendency to leakiness increases two- to three-fold during intense exercise, such as the training athletes are undergoing now to get ready for the Olympics. But if they take bovine colostrum for two weeks prior to exercise, the change in gut leakiness is almost completely prevented."

Colostrum works because it contains growth factors designed to strengthen the gut lining. That is an important part of its value for a newborn mammal, who will have a very permeable gut and needs it to toughen up fast.

For athletes who fear gastrointestinal problems such as cramps, diarrhoea and nausea, says Playford, pharmacological options to reduce the problems are limited – so there is a lot of interest in a natural product such as colostrum. However, it's not just gut problems that colostrum helps to relieve. Some of Davison's studies show that athletes who take it are as much as 20% less likely to get infections of the upper respiratory tract. "Last-minute illness is a real fear for athletes, and colostrum seems to give the immune system a boost that can reduce the risk," he says.

Away from the Olympic stadium, other people could benefit from taking colostrum too. "It could be really useful to people who have to do physical exercise in hot conditions, such as soldiers in Afghanistan," says Playford. "They are susceptible to heatstroke because of all the gear they have to wear and carry, and taking colostrum could reduce that very serious risk. Another group who could benefit are older people with arthritis who develop serious gut problems because of the strong painkillers they use, and those with ulcerative colitis. "These patients are at risk of damage to their gut lining and the colostrum helps it to heal and reduces its permeability."

Colostrum is sometimes referred to as a "nutriceutical" – half-nutrition, half-pharmaceutical. Crucial for Olympic hopefuls is the fact that – as far as scientists can tell – it doesn't introduce substances into the body that will give positive results in drugs tests. The International Olympic Committee is monitoring its use.

Jeni Pearce, a nutritionist for Team GB who is currently at the training camp at Loughborough University, says she is aware that some athletes will have used or are using the substance. "Athletes are often on a nutrition programme that has been worked out uniquely for them," she says. "And within that, colostrum could be useful – especially for those who might be at risk of leaky gut conditions."

"It seems pretty clear that there are no performance benefits. Colostrum isn't going to make a competitor go faster or stronger or longer. And it isn't something they would take as a one-off – it would be part of their diet for a while, to help them cope at times when they were really stressed."