According to the latest Australian research the immune system of long-distance runners was enhanced by probiotics - dietary supplements containing potentially beneficial bacteria or yeasts.
In a study by researchers at the Australian Institute of Sport in Canberra, twenty elite male athletes, competing in events ranging from the 800m to marathons, were enrolled in an experiment that coincided with intensive winter training programs.
The athletes were either given the probiotic Lactobacillus fermentum in freeze-dried powder as gelatin capsules, or a fake lookalike capsule called a placebo that contained harmless starch.
Lactobacillus fermentum is a lactic acid bacterium that is considered to be a useful treatment for diarrhoea and other gut infections.
Probiotics are becoming more common in food products, mainly Lactobacilli which is the germ that provides the sour taste in yoghurt and other fermented dairy foods; it is believed they strengthen gut flora and boost the immune system against disease.
Neither the athletes nor the researchers knew who received which capsules or when.
Experts suggest that extreme and intensive exercise can subdue the normal immune system, making elite athletes vulnerable to respiratory viruses.
The athletes took the capsules daily for a four-week period, followed by a four-week "washout period" in which they took nothing; they then took the placebo for four weeks, followed by another "washout."
Lead researcher David Pyne says although the bug did not change athletic performance it did reduce respiratory illness.
It was found that seven of the runners reported having respiratory problems, such as a sore throat, a cough, runny nose, chest congestion and sneezing on days when they took the placebo.
These problems were recorded on a total of 72 days and rated on average 1.7 on a scale of severity, where three was the highest mark.
But when they took the probiotics, only three of the runners reported respiratory problems and the symptoms occurred on only 30 days and rated 1.0 for severity.
Blood tests revealed that levels of interferon gamma, an important immune-system molecule in the fight against viral infection, doubled during the "probiotic" period.
The researchers found the athletes given a probiotic supplement suffered less severe flu and cold symptoms than other athletes and their illness also generally lasted only half the time of those not taking the supplement.
Dr. Pyne says probiotics appear to increase systemic immunity, possibly by boosting the activity of T-cells.
They suggest the improvement in resistance to common illnesses constitutes an "important benefit to elite athletes undertaking high level training in preparation for national and international competitions.
The study is published in the British Journal of Sports Medicine.
However another study by Dutch researchers, warns against using probiotics to treat patients with a dangerous disease of the pancreas called severe acute pancreatitis.
They say more than twice as many patients with the condition given probiotic supplements to prevent infections died compared to those who received placebos.
Among 296 volunteers, 24 people among the probiotics group died, a mortality rate of 16 percent, compared with nine (six percent) in the placebo group.
This study is published in The Lancet.