The use of probiotics to prevent or treat mastitis is widespread, but what is known about the evidence for probiotics in mastitis? The latest protocol from the Academy of Breastfeeding Medicine (Protocol #36: The Mastitis Spectrum) (1) recommends considering the use of probiotics to treat infectious mastitis. But what is the level of evidence for the use of probiotics, and do they have any side effects?

A systematic review and meta-analysis assessing probiotics’ preventive and therapeutic effects on mastitis has recently been published (2). In this study, only six randomised clinical studies could be included for analysis, of which only three assessed the effect of probiotics on the incidence of mastitis, two on the incidence of breast pain and five on the bacterial count in breast milk.

The meta-analysis concluded that the use of probiotics decreases the incidence of mastitis by 50% (relative risk = 0.49, and confidence interval = 0.35-0.69) and decreases bacterial counts in women without mastitis symptoms (mean reduction -0.23 cfu/mL, CI -0.23- -0.16) and women with mastitis (mean reduction -0.89 cfu/mL, CI -1.34- -0.43). In contrast, it was found not to affect the incidence of mammary gland pain.

Despite these positive results, it is worth highlighting that the number of clinical studies is minimal and that there has been no significant scientific contribution in recent years. In fact, a systematic review on the same topic was published in 2020 (3) and included the same studies.

Compared to this publication, the 2022 article (2) only provides data from one new study, the others are exactly the same as those published between 2008 and 2017, and coincidentally all were conducted in Spain and by the same research group. This means that the results may be biased by the population studied. Therefore, it is important that more research groups worldwide provide evidence on the efficacy of probiotics to prevent or treat mastitis.

On the other hand, the 2020 systematic review on probiotics (3) already warned that published studies on the efficacy of probiotics for mastitis had limitations. They were the inadequate description of the population studied, low sample size, lack of power and sample size calculations, lack of randomisation in some studies and use of different definitions of mastitis, which makes it difficult to compare between studies.

Other clinical studies are ongoing. For example, the Nassar research team have conducted a clinical study to investigate the efficacy of probiotics in preventing mastitis (4). This study has now been completed, and they have recruited 620 lactating women divided into two study groups (placebo and probiotics). However, the results of this study have yet to be available.

Another important aspect of taking probiotics for mastitis is the possible side effects they may cause. The two systematic reviews point out that the included studies reported no significant side effects, and only one study described the appearance of wind in breastfeeding women. However, a Cochrane library review looking at probiotic use in pregnant women to prevent gestational diabetes concluded that probiotic use during pregnancy might increase the risk of pre-eclampsia (5).

With all these findings and data, we can conclude that the current evidence on using probiotics to prevent or treat mastitis is limited. More well-designed randomised clinical trials are needed to make reliable recommendations.

Even so, in daily clinical practice, we know that they are used because of their easy accessibility or because of the sense of security they give.

We look forward to the publication of the results of the studies that are currently underway to be able to establish more precise recommendations in the future.

References:

1. Mitchell KB, Johnson HM, Rodríguez JM, Eglash A, Scherzinger C, Zakarija-grkovic I, et al. Academy of Breastfeeding Medicine Clinical Protocol #36: The Mastitis Spectrum, Revised 2022. Breastfeed Med [Internet]. 2022;17(5):360–76.

2. Yu Q, Xu C, Wang M, Zhu J, Yu L, Yang Z, et al. The preventive and therapeutic effects of probiotics on mastitis: A systematic review and meta-analysis. Perna S, editor. PLoS One. 2022 Sep 9;17(9):e0274467.

3. Barker M, Adelson P, Peters MDJ, Steen M. Probiotics and human lactational mastitis: A scoping review. Women and Birth. 2020;33(6):e483–91.

4. Bond DM, Morris JM, Nassar N. Study protocol: evaluation of the probiotic Lactobacillus Fermentum CECT5716 for the prevention of mastitis in breastfeeding women: a randomized controlled trial. BMC Pregnancy Childbirth. 2017 May 19;17(1).

5. Davidson SJ, Barrett HL, Price SA, Callaway LK, Dekker Nitert M. Probiotics for preventing gestational diabetes. Cochrane Database Syst Rev. 2021 Apr 19;2021(4).