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Probiotics are live micro-organisms that when given in adequate amounts can cause health benefits. The safety and efficacy of probiotics in the prevention and treatment of various clinical conditions have been evaluated in randomised controlled clinical trials, systematic reviews and meta-analyses. Generally, their safety has been documented. As a supplement to standard rehydration therapy, probiotics have been demonstrated to shorten the duration of diarrhoea resulting from acute viral gastroenteritis and in preventing antibiotic-associated diarrhoea in healthy children. Preliminary evidence suggests that probiotics might prevent necrotising enterocolitis in very-low-birth-weight infants, but further studies are needed before definite conclusions can be drawn. Probiotics have also been assessed in the treatment and prevention of allergic disease but the results, although promising, need further confirmation. Targeting a paediatric population, probiotics have been evaluated in the treatment of irritable bowel syndrome, ulcerative colitis, Helicobacter pylori gastritis and infantile colic, but at this stage, there is no evidence to support their routine use for these indications. There is a great need for studies aiming at disentangling the mechanisms by which probiotics mediate their clinical effects and for comparative studies between various probiotic bacteria. We still need to know which probiotic(s) to use and for which indications. A clearer message on dosages, optimal timing and duration of administration is needed. For this purpose, more carefully designed and sufficiently powered, randomised controlled trials with predefined outcomes are needed.

The gut microbiome interacts with the host in the metabolic response to diet, and early microbial aberrancies may be linked to the development of obesity and metabolic disorders later in life. Probiotics have been proposed to affect metabolic programming and blood lipid levels, although studies are lacking in infants. Here, we report on the lipid profile and global metabolic response following daily feeding of probiotics during weaning. A total of 179 healthy, term infants were randomised to daily intake of cereals with (n 89) or without (n 90) the addition of Lactobacillus paracasei ssp. paracasei F19 (LF19) 108 colony-forming units per serving from 4 to 13 months of age. Weight, length and skinfold thickness were monitored. Venous blood was drawn at 5·5 and 13 months of age for analysis of the serum lipid profile. In a subsample, randomly selected from each group, GC-time-of-flight/MS was used to metabolically characterise plasma samples from thirty-seven infants. A combination of multi- and univariate analysis was applied to reveal differences related to LF19 treatment based on 228 putative metabolites, of which ninety-nine were identified or classified. We observed no effects of probiotic feeding on anthropometrics or the serum lipid profile. However, we detected significantly lower levels of palmitoleic acid (16 : 1) (P < 0·05) and significantly higher levels of putrescine (P < 0·01) in LF19-treated infants. Palmitoleic acid is a major MUFA strongly linked to visceral obesity, while putrescine is a polyamine with importance for gut integrity. Whether the observed differences will have long-term health consequences are being followed.

Background: Long-term effects of probiotics in primary prevention of allergic disease need further evaluation. We previously reported a reduced cumulative incidence of infant eczema by feeding Lactobacillus paracasei ssp paracasei F19 (LF19) during weaning. Therefore, we assessed effects of LF19 on the prevalence of allergic disease at school age. Methods: In a double-blind placebo-controlled trial infants were randomized to daily intake of cereals with (n=89) or without LF19 10(8) CFU (n=90) from 4-13months of age. At age 8-9, we evaluated the prevalence of allergic disease (eczema, allergic rhinitis, asthma, and food allergy) by clinical examination and validated questionnaires. IgE sensitization was assessed by skin prick test (inhalant allergens) and specific IgE levels (food allergens). Lung function was evaluated by a spirometry reversibility test. Fractional exhaled nitric oxide (FENO) was measured. Results: Of 171 children that completed the intervention, 121 were assessed at age 8-9. In the probiotic group, 15/59 (25%) were diagnosed with any allergic disease vs 22/62 (35%) in the placebo group [OR (95% CI) 0.62 (0.28-1.36)]. Corresponding numbers for IgE-associated allergic disease were 9/53 (17%) vs 12/59 (20%) [0.80 (0.31-2.09)]. Median (25th-75th percentile) FENO was 9 (8-12) in the probiotic vs 8 (7-12) ppb in the placebo group (P>0.05). There was no effect of LF19 on lung function measures (P>0.05). Conclusions: There was no long-term effect of LF19 on any diagnosed allergic disease, airway inflammation or IgE sensitization. This suggests delayed eczema onset but to fully examine long-term benefits a larger study population had been needed.

Antioxidant intakes in pregnancy may influence fetal immune programming and the risk of allergic disease. We investigated associations between maternal intakes of β-carotene, vitamin C, vitamin E, copper and zinc, and infant allergic outcomes. Antioxidant intakes of pregnant women (n = 420) assessed prospectively by a food frequency questionnaire, were examined in relation to allergic outcomes at 1 year of age (n = 300). The main relationships with allergic outcomes were seen with dietary vitamin C and copper. Specifically, higher maternal dietary vitamin C intake was associated with a reduced risk of any diagnosed infant allergic disease and wheeze. After adjustment for potential confounders the relationship with wheeze remained statistically significant. There was also an inverse linear relationship between vitamin C and food allergy. Higher dietary copper intake was associated with reduced risk of eczema, wheeze and any allergic disease. The relationship with wheeze and any allergic disease remained statistically significant in multivariate analysis, and there was also an inverse linear relationship between copper and food allergy. However, these relationships were only seen for nutrients present in food. There were no relationships between β-carotene, vitamin E or zinc and any allergic outcomes. In summary, this study suggests that maternal diet of fresh foods rich in vitamin C is associated with reduced risk of infant wheeze, and that copper intake is associated with reduced risk of several allergic outcomes.

Background: We previously reported that feeding the probiotic Lactobacillus paracasei ssp. paracasei F19 (LF19) during weaning reduced the cumulative incidence of eczema. Objective: To investigate the impact of feeding LF19 on T-cell maturation. Methods: One hundred and seventy-nine healthy, term infants with no prior allergic manifestations were randomized to daily intake of cereals with (n = 89) or without (n = 90) the addition of LF19 108 colony forming units per serving from 4 to 13 months of age. Venous blood was drawn at 5.5 and 13 months of age. We used the cytokine response to polyclonal T-cell stimulation by anti-CD3 plus anti-CD28 monoclonal antibodies, and in vitro stimulation with the vaccine tetanus toxoid (TT) as measures of global adaptive immunity and capacity to raise a specific T-cell response, respectively. Expression levels of IL-2, IFN-γ, IL-4, IL-17A and IL-10 messenger RNAs (mRNAs) were used as proxies for general T-cell stimulation and naive Th0 cells, Th1-, Th2-, Th17- and T regulatory lineages. Results: There was no difference between the two groups at 5.5 months of age. At 13 months, the polyclonal IL-2 response was higher in the placebo group (P < 0.05), whereas the IFN-γ/IL-2 (P < 0.01) and IL-17A/IL-2 (P < 0.05) ratios after polyclonal stimulation were higher in the probiotic group, as was the TT-specific IL17-A response (P < 0.001). In both groups, the IFN-γ and IL-4 responses increased from 5.5 to 13 months upon both polyclonal and specific stimulation (P < 0.01), whereas the IL-10 response remained low (P > 0.05). Conclusion and Clinical Relevance: Our findings suggest modest effects by probiotics on T-cell maturation following 9 months of probiotic intake. Future studies should address if specific probiotics may drive immune development with possible preventive effects on the development of allergic disease.

Emerging evidence suggests that exposures during pregnancy and the early postnatal period can modify gene expression and disease propensity. Diet is a major environmental exposure, and dietary factors, including polyunsaturated fatty acids, probiotics, oligosaccharides, antioxidants, folate, and other vitamins, have effects on immune function. Some also have been implicated in reduced risk of allergy in observational studies. Intervention trials with polyunsaturated fatty acids, probiotics, and oligosaccharides suggest preliminary but as-of-yet-unconfirmed benefits. Food allergen avoidance during pregnancy, lactation, or infancy has provided no consistent evidence in allergy prevention and is no longer recommended. Rather, there is now a focus on food allergens in tolerance induction. Specific nutrients can induce changes in gene expression during early development and have been implicated in potentially heritable "epigenetic" changes in disease predisposition. Collectively, these observations emphasize that early exposures may modify tolerance development and that further research on these exposures should remain a priority.

PURPOSE OF REVIEW: Diet is arguably one of the most significant environmental exposures during early development. Here, we explore the effects of key perinatal dietary exposures on immune development and susceptibility to allergic disease. RECENT FINDINGS: Dietary changes are at the centre of the emerging epigenetic paradigms that underpin the rise in many modern diseases. There is growing evidence that exposures in pregnancy and the early postnatal period can modify gene expression and disease susceptibility. Specific nutrients, including antioxidants, oligosaccharides, polyunsaturated fatty acids, folate and other vitamins, have documented effects on immune function. Some have also been implicated in modified risk of allergic disease in observational studies. Intervention studies are largely limited to trials with polyunsaturated fatty acids and oligosaccharides, showing preliminary but yet unconfirmed benefits in allergy prevention. Avoidance of food allergens in pregnancy, lactation or infancy has provided no clear evidence in allergy prevention and is no longer recommended. Rather there is focus on their role in tolerance induction. SUMMARY: Modern dietary changes are clearly implicated in the rising propensity for inflammatory immune responses. These dietary changes, which appear to be providing less tolerogenic conditions during early immune programming, may provide important avenues for preventing disease.

A reduced microbial load early in life has been suggested to be linked to the increasing prevalence of allergic diseases in the industrialized world. Some studies have indicated that probiotics may be effective in the prevention of eczema. In vitro studies indicate that probiotics have immunomodulatory effects. In the present study, we evaluated the effects of feeding Lactobacillus F19 during weaning on the incidence of eczema and Th1/Th2 balance. In a double-blind, placebo-controlled randomized intervention trial, infants were fed cereals with (n = 89) or without Lactobacillus F19 (n = 90) from 4 to 13 months of age. We assessed the cumulative incidence of eczema at 13 months of age. The ratio of interferon-gamma (IFN-gamma) to interleukin 4 (IL4) mRNA expression levels in polyclonally stimulated peripheral blood T cells was used as a proxy for immune balance. Total and specific IgE serum levels were also assessed. The cumulative incidence of eczema at 13 months was 11% (4-17%, 95% CI) and 22% (13-31%, 95% CI) in the probiotic and placebo groups, respectively (p < 0.05). The number needed to treat was 9 (6.5-11.5, 95% CI). At 13 months of age, the IFN-gamma/IL4 mRNA ratio was higher in the probiotic compared with the placebo group (p < 0.05). In contrast, there were no differences between groups in serum concentrations of IgE. In summary, feeding Lactobacillus F19 during weaning could be an effective tool in the prevention of early manifestation of allergy, e.g., eczema. The higher Th1/Th2 ratio in the probiotic compared with the placebo group suggests enhancing effects of Lactobacillus F19 on the T cell-mediated immune response.

Microbial exposure is necessary for the development of normal immune function, which has driven the idea of using probiotics for treatment and prevention of immune-mediated diseases in infancy and childhood. Mounting evidence indicates that probiotics have immunomodulatory effects. However, the mechanisms are still poorly understood. Specific antibody response is a valuable proxy for immune system maturation status in infancy. We aimed at determining the impact of Lactobacillus F19 (LF19) during weaning on infections and IgG antibody responses to routine vaccines. In a double-blind, placebo-controlled randomized intervention trial, infants were fed cereals with (n = 89) or without LF19 (n = 90) from 4 to 13 months of age. Infants were immunized with DTaP (diphtheria and tetanus toxoid and acellular pertussis), polio and Hib-conjugate vaccines at (3), 5(1/2) and 12 months of age. We assessed the number of days with infections, antibiotic prescriptions and antibody concentrations to Hib capsular polysaccharide (HibPS), diphtheria toxin (D) and tetanus toxoid (T) before and after the second and third doses. Days with infectious symptoms did not differ between the groups. Days with antibiotic prescriptions were fewer in the LF19 group (p = 0.044). LF19 enhanced anti-D concentrations when adjusting for breastfeeding duration and colonization with LF19 (p = 0.024). There was an interaction of the intervention and colonization with LF19 on anti-T concentrations during the course of vaccination (p = 0.035). The anti-HibPS concentrations were higher after the first and second dose of Hib vaccine in infants breastfed <6 months compared with those breastfed > or =6 months (p < 0.05), with no effect by LF19. In conclusion, feeding LF19 did not prevent infections, but increased the capacity to raise immune responses to protein antigens, with more pronounced effects in infants breastfed <6 months.

Diet is one of the determinants of gut microbial composition. Reported changes in the biodiversity of the gut microbiota in the obese have spurred interest in gut microbiota modulation by dietary interventions. Using an untargeted metabolomics approach, we previously reported that infant cereals with the probiotic Lactobacillus paracasei ssp. paracasei F19 (LF19) fed daily from 4 to 13 months of age affected the plasma metabolome with lower levels of fatty acids associated with obesity indices compared with placebo. The study participants were invited to a follow-up study at 8-9 years of age and 120 children participated. Venous blood was drawn after overnight fasting and plasma samples were available from 112 children. Samples were analysed using GCxGC-time-of-flight/MS for characterisation of the global plasma metabolome. A combination of multivariate and univariate analysis was used to reveal differences between the LF19 and placebo group, and according to weight class and sex. The lower levels of palmitic acid and palmitoleic acid in the LF19 group during the intervention did not remain at the follow-up. Stronger models according to weight class and sex were obtained. BMI was associated with several metabolites including the branched-chain amino acids leucine and isoleucine, and the aromatic amino acids, tyrosine and phenylalanine. Collectively, feeding LF19 during weaning induced transient effects on the plasma metabolome. The disparities seen in the metabolic profile of overweight/obese young school children underscore the need for effective early preventive and treatment strategies.