Athletes undertaking endurance training over the winter months could benefit from a daily probiotic drink to cut their risk of colds and other similar infections according to the results of a recent cliinical trial.

The term probiotic refers to foods or dietary supplements that contain beneficial bacteria which are normally found in the body. Fermented milk products such as yoghurt, sour cream, buttermilk and Yakult are examples of foods that may act as probiotics. Although probiotics are not considered essential to health, the microorganisms they contain may assist with digestion or help protect against harmful bacteria by improving the workings of the immune system.

Probiotics are increasingly being used and evaluated in the treatment of a range of medical conditions including inflammatory bowel disease, diarrhoea, gastroenteritis, infant allergies, lactose malabsorption and irritable bowel syndrome. The best evidence to date supports a benefit for probiotics in the prevention and treatment of infectious diarrhoea in children, with emerging research supporting benefits in other areas.

A recent clinical trial published in the International Journal of Sport Nutrition and Exercise Metabolism examined the benefits of daily probiotic supplementation (using the commercially available Yakult drink) taken over 4 months during winter in a group of 84 athletes.

All athletes were actively training in endurance-based sports such as cycling, distance running or swimming. Because of the demands of training, this group of athletes is especially prone to upper respiratory tract infections such as the common cold.

Athletes were randomly allocated to consume daily either the probiotic drink or a placebo. Importantly, both the athletes and the researchers were blinded to the treatment each person received to remove any subjective bias about the presence and severity of any infections.

What the study found

Athletes consuming the probiotic drink were 27% less likely to experience an upper respiratory tract infection for a week or longer over the study period compared to the placebo group. The number of infections was close to half in the probiotic group compared to the placebo group.

Salvia samples showed that a marker of a more active immune system was higher in those consuming the probiotic drink, though a battery of blood tests for other immune markers failed to show a difference between the groups.

When an infection struck though, both groups experienced a similar level of severity and duration of the infection though interestingly, those taking the probiotic reported that their training was less affected.

What it all means

There are a whole range of pills and potions that athletes consume that have little evidence of having much of benefit on performance. The evidence emerging from the field of probiotic research though is painting a very different picture and indicates that daily probiotic consumption may support an immune system already stressed from the demands of training to better protect the athlete from respiratory tract infections.