All included adults older than 18 who used probiotic products with live bacteria. The studies tested various probiotics in varying amounts, mostly strains of Lactobacillus consumed in dairy products.
Eight of the nine studies found reductions in blood pressure. Over all, compared with control groups, the use of probiotics reduced systolic blood pressure (the top number) by an average of 3.56 millimetres of mercury and diastolic pressure by 2.38.
These are modest reductions, but the scientists suggest that there is a potential for greater effect when blood pressure is elevated to begin with, when multiple species or large quantities of bacteria are consumed or when probiotics are used for longer than two months. The analysis was published in the journal Hypertension.