Can probiotics restore the vaginal microbiota? Promising treatment for HPV infection
HPV stands for Human Papillomavirus, and this is the main cause of cervical cancer. An interesting fact is that nearly every sexually active person catches it! However, our immune system can clear most of the HPV infections without any complications within 6-18 months. Only a small part of infections will progress to precancer and, ultimately, to Cervical Intraepithelial Neoplasia (NIC) and cervical cancer.
What are the factors involved in the development of cervical cancer?
- Female hormones (oestrogen and progesterone)
- Inflammation levels in the vagina
- Oral contraceptives
- Vaginal microbiota1
The role of vaginal Microbiota
Surprisingly, women without cervical abnormalities have different vaginal microbiota than women with precancer and cervical cancer. Research shows that vaginal microbiota plays a big role in the persistence or clearance of HPV.1, 2
Scientists have classified the vaginal microbiota in five different “community state types” (CSTs):
- CSTs I, II and V are dominated by Lactobacillus species: L. crispatus, L. gasseri and L. jensenii, respectively. Healthier women tend to have these.1, 3
- CTS III has a higher prevalence of L. iners. Research has been inconclusive so far, we don't know yet whether this bacteria is associated with health or disease.4, 5
- CTS IV is characterized by lower amounts of Lactobacillus and, instead, prevalence of bacteria associated with bacterial vaginosis (BV), such as Gardnerella, Megasphera, Sneathia and Prevotella.1
As a summary, healthier vaginal states are associated with:
- Lower microbial species diversity.
- Higher levels of Lactobacillus species (especially those dominating CTSs I, II and V).3, 6, 7
- Absence or low levels of bad bacteria such as Sneathia or Gardnerella vaginalis.8
Lactobacillus, a promising probiotic candidate for HPV infections
Vaginal Lactobacillus species have different mechanisms that fight bad bacteria:
- Produce lactic acid which lowers the pH and inhibits the growth of other bacteria.9
- Produce bacteriocins, proteins with antibacterial activity.
- Compete for adhesion sites to the vaginal epithelial cells.1, 10
Research is ongoing with a focus on L. gasseri, L. crispatus, L. jensenii and L. casei. In vitro studies have shown the inhibitory effects of these strains on cervical cancer cells.9
In a study, 65 HIV-infected women with an aberrant microbiota took a daily probiotic containing Lactobacillus rhamnosus GR-1 and L. reuteri RC-14 for 6 months. In the probiotic group, prevalence of Lactobacillus in the vaginal microbiota was observed.11
In another study, 54 women with HPV infection, took the commercial probiotic Yakult (L. casei Shirota) for 6 months. Probiotic users had double the chance of clearance of cytological abnormalities (60% vs 31%).12
L. crispatus seems to be a promising probiotic candidate. While bacterial communities in CSTs can change into CST IV and cause persistence of HPV virus, L. crispatus is the least likely to make this transition.13 This strain produces a specific protein which helps in the attachment to the intestinal and vaginal mucosa, thereby competing for space with other bacteria.8
Limitations of recent research in the “Oncobiome” (microbiota associated with cancer development)
Studies are observational, which means that it is only possible to associate bacteria with the disease, but causality can’t be demonstrated.
Here are my top tips to increase good bacteria in your vaginal microbiota!
- Eat more fruits and vegetables. These contain micronutrients that may help in preventing cellular DNA damage, which has been linked to HPV infection.12
- Supplementation with probiotics (Lactobacillus species) might be useful for restoring your vaginal microbiota and, therefore, controlling HPV infection.10 The treatment should be at least 6 months since research has seen the best results with long-term approaches.10,11, 12
- Consume prebiotic foods. Research has shown that some prebiotics (FOS and GOS) promote the growth of L. crispatus, L. jensenii and L. vaginalis, but not pathogenic bacteria such as Candida albicans, Escherichia coli or Gardnerella vaginalis.14
- Get checked every year by your gynaecologist. Monitoring is key when it comes to HPV.