Probiotic milk drinks nudge blood pressure down

Blood pressure is one of the most consequential numbers in health, and even small population-wide reductions translate into meaningfully fewer strokes and heart attacks. Earlier studies had suggested that fermented milk containing probiotic bacteria might have blood pressure-lowering properties, possibly through compounds produced during fermentation, but individual trials were small and their results varied. This meta-analysis set out to pool all the randomised evidence and answer two questions: does the effect hold up, and how big is it really?

The researchers searched PubMed, the Cochrane Library and ClinicalTrials.gov up to March 2012, and also combed the reference lists of the papers they found. They included randomised placebo-controlled trials of probiotic fermented milk that measured blood pressure, arriving at 14 trials with 702 participants in total. Results were combined using either a fixed-effects or random-effects statistical model as appropriate, and the team ran subgroup and sensitivity analyses to probe whether the findings held across different populations and trial sizes.

Compared with placebo, probiotic fermented milk reduced systolic blood pressure by 3.10 mmHg and diastolic blood pressure by 1.09 mmHg. Subgroup analyses suggested a slightly greater systolic effect in hypertensive participants than in those with normal blood pressure, and trials conducted in Japan showed larger reductions than those run in European countries. Some evidence of publication bias was present, but a sensitivity analysis excluding small trials with extreme results changed the pooled estimate only minimally.

This analysis supports the idea that fermented dairy with live cultures has a genuine but modest effect on blood pressure, particularly in people at the pre-hypertensive or hypertensive end of the range. The geographic split, with Japanese trials showing bigger effects than European ones, raises open questions about whether specific bacterial strains, products or diets explain the difference. It also leaves unanswered how long the effect persists, and whether it translates into fewer cardiovascular events rather than just a better reading.

If your blood pressure sits on the high side, this is a reason to view probiotic fermented milk as a small, food-based helper rather than an alternative to anything your doctor has advised. The size of the effect is modest, in the region of a few mmHg, and it appeared strongest in people whose pressure was already raised. For someone with normal blood pressure, the expected benefit is smaller still.