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Katja Hatakka a Valio Research and Development, PO Box 30, FIN-00039 Valio, Helsinki, Finland, b Hospital for Children and Adolescents, Helsinki
University Central Hospital, FIN-00029 Helsinki, Finland, c Centre of the
Environment, Helsinki City, Helsinginkatu 24, FIN-00530 Helsinki,
Finland, d STAT-Consulting, Takojankatu 15 B, FIN-33540 Tampere, Finland, e Department of Oral and Dental Diseases, Helsinki University
Hospital, PO Box 263, FIN-00029 HUS, Helsinki, Finland, f Helsinki City Health Department, Kytösuontie 9, FIN-00030
Helsinki, Finland, g Foundation for
Nutrition Research, PO Box 30, FIN-00039 Helsinki, Finland
Correspondence to: R Korpela riitta.korpela{at}valio.fi
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Abstract |
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Objective:
To examine whether long term
consumption of a probiotic milk could reduce gastrointestinal and
respiratory infections in children in day care centres.
Design:
Randomised, double blind, placebo controlled study over seven months.
Setting:
18 day care centres in Helsinki, Finland.
Participants:
571 healthy children aged 1-6 years: 282 (mean (SD) age 4.6 (1.5) years) in the intervention group and 289 (mean (SD) age 4.4 (1.5) years) in the control group.
Intervention:
Milk with or without
Lactobacillus GG. Average daily consumption of milk in both
groups was 260 ml.
Main outcome measures:
Number of days with respiratory
and gastrointestinal symptoms, absences from day care because of
illness, respiratory tract infections diagnosed by a doctor, and course
of antibiotics.
Results:
Children in the Lactobacillus
group had fewer days of absence from day care because of illness (4.9 (95% confidence interval 4.4 to 5.5) v 5.8 (5.3 to 6.4)
days, 16% difference, P=0.03; age adjusted 5.1 (4.6 to 5.6)
v 5.7 (5.2 to 6.3) days, 11% difference, P=0.09). There was
also a relative reduction of 17% in the number of children suffering
from respiratory infections with complications and lower respiratory
tract infections (unadjusted absolute % reduction
8.6 (
17.2 to
0.1), P=0.05; age adjusted odds ratio 0.75 (0.52 to 1.09), P=0.13)
and a 19% relative reduction in antibiotic treatments for respiratory
infection (unadjusted absolute % reduction
9.6 (
18.2 to
1.0),
P=0.03; adjusted odds ratio 0.72 (0.50 to 1.03), P=0.08) in the
Lactobacillus group.
Conclusions:
Lactobacillus GG may reduce
respiratory infections and their severity among children in day care.
The effects of the probiotic Lactobacillus GG were modest
but consistently in the same direction.
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What is already known on this topic
What this study adds
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Introduction |
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Children attending day care centres have a 1.5-3.0 times higher risk of gastrointestinal and respiratory tract infections than children cared for at home or in small family care groups.1-6 Increased risk of disease has obvious public health and economic consequences, such as direct medical costs as well as the indirect costs of parents having to take time off work to look after sick children.7-9 Prevention of infections in day care is therefore of major importance.
Probiotic bacteria, which beneficially affect the host by improving the
intestinal microbial balance, may affect the immune response.
Lactobacillus rhamnosus GG, ATCC 53103, a probiotic strain of human origin with widely documented health
effects,10 influences immune response, both specifically
by stimulating antibody production11 and non-specifically
by enhancing the phagocytic activity of the blood
leucocytes.12 It promotes recovery from rotavirus
diarrhoea11 and reduces the incidence of diarrhoea associated with use of antibiotics in children.
13 14
However, most studies of probiotic bacteria have been short term
trials. Over a seven month winter period we examined the effect of
consumption of milk containing probiotic bacteria on the incidence of
gastrointestinal and respiratory infections in children attending day
care centres.
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Methods |
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Participants
This randomised, double blind, placebo controlled clinical study
was carried out in 18 municipal day care centres, in similar
socioeconomic areas in north, west, and north east Helsinki. Children
aged 1-6 years were recruited through meetings with parents. We
excluded children with allergy to cows' milk, lactose intolerance,
severe food allergy, and other severe chronic diseases. All the healthy
children whose parents gave informed consent were randomised for the
trial (n=594). The study protocol was approved by the ethics committee
of Helsinki City Health Department.
Intervention
The intervention lasted seven months over the winter. The
Lactobacillus milk (Gefilus, Valio, Riihimäki, Finland)
contained 1% fat and 5-10x105 colony forming
units/ml of strain Lactobacillus rhamnosus GG (ATCC 53103). The control milk had the same composition but without Lactobacillus. Milk types were deliverd in cartons coloured
yellow or green. The day care staff, parents, children, and
investigators were unaware of which milk carton contained
Lactobacillus until the intention to treat analysis was performed.
Data collection
We collected background information on the family, their
environment, the child's nutrition habits, and illnesses. During the
study, parents recorded daily in a symptom diary any respiratory
symptoms (fever, runny nose, sore throat, cough, chest wheezes,
earache) and gastrointestinal symptoms (diarrhoea, vomiting, stomach
ache). They also reported absences from the day care centre, doctors'
diagnoses, and prescriptions of antibiotics. A questionnaire at the end
of the study collected information on general health and the use of
other products that contained lactic acid bacteria during the study.
Faecal samples were collected at the beginning, middle, and end of the
study. We randomly selected 100 samples to study the recovery of
Lactobacillus GG in the faeces to confirm compliance.
15 16
Sample size and randomisation
We calculated sample size on the assumption that the use of
Lactobacillus GG would result in a 20% reduction in
respiratory tract infections. Pönkä et al reported a mean (SD) of
3.3 (2.3) episodes of illnesses among day care children during an eight
month follow up.17 We estimated that, with a power of 90%
and at a significance level of 0.05, we needed 250 children per group
to show a 20% difference between the groups. Each child was randomly
allocated to the Lactobacillus or the control group according to a computer generated, blocked randomisation list. We used
a block size of four, stratified according to age (<3 years and 3 years and over) and day care centre (18 centres).
Outcome measures
The primary outcome measures were the number of days with
respiratory and gastrointestinal symptoms or days with any illness;
absences from day care centre because of illness; number of children
with upper respiratory tract infections with complications (acute
otitis media and sinusitis) and lower respiratory tract infections
(acute bronchitis and pneumonia) as diagnosed by a doctor; and
antibiotic treatments during the seven month intervention. A secondary
outcome was the correlation between the amount of milk consumed and the
number of days with symptoms. We also defined a symptom score to
measure the overall burden of symptoms (sum of all recorded symptoms,
daily range 0 to 9).
Statistical analysis
The distribution of the number of days of illness, days with
respiratory and gastrointestinal symptoms, and the symptom scores and
days of absence due to illness were skewed to the right and were
logarithmically transformed. The results are given as geometric means
with 95% confidence intervals. We used the t test for
independent samples to compare the groups. To control for differences
in the age distribution, we analysed the logarithmic transformed
variables using analysis of covariance, in which we included age as a
continuous covariate. We then transformed the age adjusted means and
confidence intervals back to the original scales. Treatment differences
are given as the geometric mean of the ratio
(Lactobacillus:control) with 95% confidence intervals.
2 test or
Fisher's exact test. We used logistic regression analyses to control
for age. Partial correlations were calculated between milk consumption
and the numbers of days with illness, adjusted for age. All analyses
were based on the intention to treat population. Statistical analyses
were performed with SPSS (release 9.0).
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Results |
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Of the 594 children randomised, 571 started the study, receiving either milk containing Lactobacillus GG (n=282) or control milk (n=289) (figure 1). Fifty eight children did not complete the follow up period.
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Table 1 details characteristics of the children before treatment. The block randomisation resulted in a similar distribution of children in the age groups under 3 years and 3 years and over: 51 (18%) and 231 (82%) in the Lactobacillus group and 55 (19%) and 234 (81%) in the control group. Detailed analysis of age distribution, however, showed that there were differences between the groups. Also, there were more children in the control group who had had five or more respiratory infections during the preceding 12 months. Age and preceding infections both have an effect on the incidence of infections and as they were strongly correlated we adjusted only for age in comparisons of treatment.
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Intention to treat analysis
Symptoms of illness as reported by parents
There were
no significant differences between the groups in the number of days
with respiratory and gastrointestinal symptoms (table 2). However, in
the Lactobacillus group there were fewer days of absence
because of illness
a Lactobacillus:control ratio of 0.85 (95% confidence interval 0.73 to 0.98)
and thus a reduction of 15%.
The time without respiratory symptoms was significantly longer in the
Lactobacillus group compared with the control group (5 (4.1 to 5.9) v 4 (3.5 to 4.6) weeks, P=0.03, fig 2). Time
without diarrhoea was not significantly different (25 (24 to 26)
v 24 (23 to 25) weeks, respectively, P=0.20, fig
2).
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The number of children with respiratory infections (otitis media, sinusitis, bronchitis, and pneumonia) was significantly lower in
the Lactobacillus group (relative reduction 17%, table 3).
There were also fewer children in the Lactobacillus
group who were prescribed antibiotics for respiratory infections
(relative reduction 19%, table 3).
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Adjustment for age reduced the
difference between the groups in the number of days of absence (table 2). After age adjustment the odds ratio for the
Lactobacillus group was 0.89 (0.77 to 1.02). The time
without respiratory symptoms was not significantly different between
the groups (data not shown), but for the Lactobacillus group
the estimated odds ratio was 0.86 (0.70 to 1.06, P=0.16), indicating
reduced risk. Time without diarrhoea was also not significantly
different between the groups, but the odds ratio for the
Lactobacillus group was 0.87 (0.64 to 1.28, P=0.36). The
numbers of children with respiratory tract infections diagnosed by a
doctor and being given antibiotic treatments for these were not
significantly different between the groups (table 3). However, the
age adjusted odds ratios for the Lactobacillus group were
0.75 (0.52 to 1.09, P=0.13) for all respiratory infections and 0.72 (0.50 to 1.03, P=0.08) for antibiotic treatment for respiratory infection.
Secondary analyses
After age adjustment there was a negative but non-significant
correlation between the amount of milk consumed and the total number of
days of illness (r=
0.12; P=0.07) and days with
respiratory symptoms (r=
0.11; P=0.09). The negative correlation between the amount of Lactobacillus milk
consumed and days with gastrointestinal symptoms was significant
(r=
0.17; P=0.007).
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Discussion |
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This randomised, double blind, placebo controlled study is the first to examine the long term effects of probiotic bacteria on infections in normally healthy children. The intervention lasted seven months during the season in which the infection rate is usually highest.18 Fewer children in the group taking Lactobacillus GG suffered from respiratory infections with complications, though there was no significant difference between the groups in the number of days with symptoms. We found a reduction of 21% in the occurrence of acute otitis media in the Lactobacillus group, although the difference between the groups was not significant. Complications from respiratory infections were the main indication (85%) for the use of antibiotics. Consuming Lactobacillus GG reduced such treatments. Children receiving Lactobacillus had fewer days of absence from day care because of illness, suggesting that Lactobacillus GG may lessen the severity of respiratory infections.
It is well known that age is strongly associated with the incidence of infection.19 We noticed that despite the age stratified randomisation, there were differences in the age distributions between the study groups. Although neither the mean age nor the distribution between those aged under 3 and 3 years and over differed between the groups, there were more 3 and 5 year olds in the control group and more 4 and 6 year olds in the Lactobacillus group. Because of this unintentional distribution we adjusted the analyses for age, which reduced the differences between the groups. However, the results came close to conventional significance, and the differences were consistently in favour of the Lactobacillus GG group.
Mode of action
Lactobacillus GG may influence the incidence of
infections by stimulating non-specific immunity or enhancing humoral and cellular immunity.20 This immunostimulatory
effect of bacteria has previously been shown to prevent recurrent
infections in children attending day care
centres.21 Our finding of negative
correlation between the days with gastrointestinal symptoms and the
dose of Lactobacillus milk consumed may indicate a dose
dependent response.
Socioeconomic effects
Respiratory infections in children have a major impact on families
and on society in general. In 1985 and 1986, the annual cost to
society in general due to illness in children attending Finnish
day care centres was about £650 to £2300 per child, depending on
age.8 Thus a 10-20% reduction in the incidence of
infections and absences from day care centres, which our results
indicate is possible, could have important clinical, public health, and
economic consequences.
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Acknowledgments |
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We thank research assistant Ms Anne Nyberg for arranging the intervention and creating the database; Ms Mimi Ponsonby for language editing; and the Social Department of Helsinki City, the day care centre staff, the children, and their parents for making this study possible.
Contributors: KH designed the protocol and the questionnaires, participated in the creation of the database, and wrote the paper. ES supervised the study and revised the manuscript. TP was responsible for the data analysis and wrote the sections on statistical methods. AP, JHM, and LN participated in the planning of the study and revised the manuscript. RK and MS initiated the study, participated in the planning, were responsible for the management of the study, and revised the manuscript. KH and RK are the guarantors of the paper.
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Footnotes |
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Funding: Valio Research and Development, Helsinki, Finland. The University of Helsinki and the City of Helsinki participated in the funding by providing supervision and technical help.
Competing interests: KH has been employed by Valio Research Centre for two of the past five years. MS and RK are employed by Valio Research Centre. ES has given two educational presentations on Lactobacillus GG for Valio, and TP has received consulting fees from Valio.
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References |
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(Accepted 14 March 2001)
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