Do probiotic yoghurts cut child illness?

“A daily probiotic drink can help protect young children against infections,” reported The Daily Telegraph. It said that children who start the day with a probiotic drink are 20% less likely than their classmates to suffer from ear and sinus infections.

This is a well-designed, randomised controlled trial, but the results are less significant than the headlines might imply. The study, sponsored by Danone, was in 638 healthy three to six year olds. The children were either given Actimel or an identical, inactive yoghurt drink every day for about three months. There was no change in the behaviour due to illness (as assessed by parents), but children in the probiotic group had slightly fewer common infections.

The newspaper has correctly reported the findings of this research. However, the results are only of borderline significance, and symptoms of illness were reported by the children’s parents, then interpreted by the researchers. Although the relative difference in rates of disease between the groups sounds high (19%), the absolute effects are quite small. If one child took the yoghurt every day for 100 days, they would have two fewer incidences of common infectious disease compared to those who were taking the placebo.

Where did the story come from?

The study was carried out by researchers from Georgetown University Medical Center, Washington, Pennsylvania State University, and the centre for Dairy & Food Culture Technologies.

The study is funded by the Danone Company Inc, the company that manufactures Actimel. Some of the researchers were employees of the company, although it is noted that the non-industry authors developed the initial protocol and gathered and analysed the data.

The study was published in the peer-reviewed medical journal European Journal of Clinical Nutrition.

What kind of research was this?

This double-blind, randomised controlled trial investigated whether a probiotic yoghurt drink reduced the frequency of common infections in children aged from three to six years old who attend day care or nursery school centres. The researchers were also interested in whether a reduction in illness had a knock-on effect on the children’s behaviour as assessed by their parents.

A randomised controlled trial is the best way of investigating whether the drink has any effect on health outcomes because it should balance out other potential confounders between the groups. However, the short duration of the study means that longer-term effects on health cannot be assumed.

What did the research involve?

The study enrolled 638 healthy children aged three to six who were attending day/nursery care for five days of the week in Washington DC. The children were randomised (by household) to receive either a strawberry-flavoured probiotic drink (commercially available) or placebo. The probiotic drink contained Lactobacillus casei, Streptococcus thermophilus and Lactobacillus bulgaricus cultures. The placebo was identical in appearance, taste, nutritional composition and packaging (200g bottles), but without the active probiotic components. The children were given the drink for 90 consecutive days during the colder period of the year (when instances of respiratory illness are higher). The families did not know which drink they were receiving.

Follow-up data was collected through daily diaries and regular phone calls to the children’s parents. The main outcomes of interest were whether the probiotic yoghurt drinks had an effect on behaviours that might be due to illness (eg absence from school, missed birthday parties or football games) and the rates of illness each week.

The illnesses were categorised into upper respiratory tract infections, lower respiratory tract infections and gastrointestinal tract infections, based on the health-related symptoms that parents reported each week. Upper respiratory tract infections included ear infections, sinusitis, streptococcal pharyngitis, non-strep pharyngitis, nasal discharge and laryngitis. Lower respiratory tract infections included pneumonia, influenza, coughs and breathing problems. Gastrointestinal tract infections (GITI) included gastroenteritis, diarrhoea, nausea and vomiting.

The researchers also examined absences from day care or school because of illness, or parents missing work due to the child being ill.

What were the basic results?

The groups showed no difference in changes in the children’s activity as a result of illness. The children who drank yoghurt had fewer common infections compared to the placebo group (with the yoghurt group having 19% less infections). However, this was of borderline significance (incidence rate ratio: 0.81, 95% CI 0.65 to 0.99; p=0.046).

When the researchers analysed the different types of illnesses, they found that the effect was significant for gastrointestinal tract infections and for upper respiratory tract infections. But again, both these results were of borderline significance only. There was no significant effect on rates of lower respiratory tract infection.

Some secondary outcomes, including days of medication use and use of antibiotics, were different between yoghurt and placebo group, with the probiotic yoghurt group generally using less. However, the researchers say that the absolute numbers of children in these analyses were small and that they are not clinically significant.

How did the researchers interpret the results?

The researchers conclude that “daily intake of a fermented dairy drink… showed some promise in reducing overall incidence of illness, but was primarily driven by gastrointestinal infections and there were no differences in change of behaviour”.

Conclusion

This is a well-designed randomised controlled trial. The active and control groups were mostly similar, which indicates that the randomisation had been successful. There was a significant difference between the groups in compliance to the drink they had been given, with the control group not being as compliant. However, the researchers say this is unlikely to have been because the participants knew which group they had been assigned to.

Importantly, the significant results from the study are only of borderline statistical significance. In some areas of their discussion, the researchers seem cautious about their interpretation, saying that their study shows that the dairy drink “holds promise, but has limitations in promoting the health of children aged three to six years”. They also note that the study used a specific type of probiotic strain, dose and age group, and that the findings cannot be extrapolated to other strains or outcomes. Although the relative difference in rates of disease between the groups sounds high (19%), the absolute effects are quite small. If one child took the yoghurt every day for 100 days, they would have two fewer incidences of common infectious disease compared to those who were taking the placebo.

Another point to keep in mind is that the illnesses are categorised by the researchers according to parental report, not according to an objective assessment of the child’s illness (eg examination by doctors, patient records etc).

Overall, the study indicates that in this age group, this particular type of yoghurt drink has a small beneficial effect on the rates of some common infectious diseases as reported by parents.