The 643 total participants (average ages of 4 to 11) had been diagnosed with asthma.

Some trials used various strains of Lactobacillus. The participants took 1 to 4 billion colony-forming units per day for 2 to 6 months.

Probiotics (compared with a placebo) improved the ratio of forced expiratory volume in the first second to forced vital capacity (3 studies; low-quality evidence) but did not improve forced expiratory volume in the first second (borderline statistical significance; p=0.05; 2 studies; high-quality evidence)

The risk of bias was low in 1 trial, high in 1 trial, and unclear in the other 3 trials.

Do probiotics improve asthma in children? Original paper