Subgroup analyses by species or genus (Forest plots for all subgroup analyses available in online supplemental file 1)
| Species | Studies (N) | Effect size |
| L. acidophilus | 18 (6077) | RR=0.66 (95% CI 0.54 to 0.80), p<0.0001 |
| L. bulgaricus | 7 (1996) | RR=0.60 (95% CI 0.37 to 0.97), p=0.04 |
| L. casei | 11 (3382) | RR=0.59 (95% CI 0.42 to 0.83), p=0.003 |
| L. helveticus | 2 (239) | Not significant |
| L. paracasei | 3 (665) | RR=0.60 (95% CI 0.41 to 0.88), p=0.01 |
| L. plantarum | 3 (325) | Not significant |
| L. reuteri | 1 (23) | Not significant |
| L. rhamnosus | 5 (779) | RR=0.71 (95% CI 0.52 to 0.97), p=0.03 |
| Lactobacillus spp | 28 (7851) | RR=0.63 (95% CI 0.52 to 0.76), p<0.00001 |
| S. boulardii | 9 (1827) | RR=0.63 (95% CI 0.46 to 0.86), p=0.004 |
| B. animalis ssp lactis | 6 (1351) | RR=0.70 (95% CI 0.54 to 0.91), p=0.009 |
| B. bifidum | 4 (3165) | Not significant |
| B. licheniformis | 1 (181) | RR=0.39 (95% CI 0.19 to 0.79), p=0.009 |
| B. longum | 4 (366) | RR=0.46 (95% CI 0.28 to 0.73), p=0.001 |
| B. subtilis | 1 (271) | RR=0.35 (95% CI 0.19 to 0.62), p=0.0004 |
| S. thermophilus | 6 (1917) | Not significant |
| C. butyricum | 1 (19) | Not significant |
| B. clausii | 1 (130) | RR=0.61 (95% CI 0.41 to 0.89), p=0.01 |
RR, risk ratio.