Table 2 Overall and subgroup analyses for the effect of probiotics on various outcomes in patients with Alzheimer’s disease (AD) and mild cognitive impairment (MCI)

Cognitive function

Overall

26

0.44 (0.26 to 0.61)

71

 < 0.001

Type of disease

AD and MCI

11

0.48 (0.23 to 0.72)

53.5

0.018

AD

6

0.72 (0.29 to 1.15)

59.2

0.032

MCI

9

0.28 (− 0.02 to 0.57)

82.1

 < 0.001

Sample size

 ≥ 300 participants

14

0.50 (0.20 to 0.80)

70.4

 < 0.001

 < 300 participants

12

0.40 (0.18 to 0.63)

73.7

 < 0.001

Duration

 ≥ 12 weeks

13

0.32 (0.06 to 0.58)

81.4

 < 0.001

 < 12 weeks

13

0.58 (0.43 to 0.74)

3.4

0.412