Microbes can impact our hormone production.
Until recently, synthetic oxytocin has been primarily used for labor stimulation and milk ejection. However, with ongoing research exploring oxytocin’s effects on sexual dysfunction, autism, addiction, depression, anxiety, and obesity, supplemental nasal oxytocin spray is becoming increasingly popular (despite the need for further research).³
Oxytocin is a neurohormone synthesized in the hypothalamus and released from the posterior pituitary, commonly known as the “love hormone” due to its involvement in social bonding and empathy. It is naturally released in response to sensory stimulation, such as breast-feeding and sexual activity. Exogenous oxytocin supplementation has shown promise in lowering stress (i.e. PNS activity increases, cortisol reduction) and increasing social sensitivity (both pro-social and anti-social behavior depending on the context)³.
Interestingly enough, taking exogenous oxytocin isn’t the only way to increase its levels in the body: the bacterial species Limosilactobacillus reuteri has also been shown to upregulate its endogenous production.² The ability of gut microbiome to affect host physiology is well known, and L. reuteri has been long-touted for its positive modulation of the immune system.¹ However, the population of L. reuteri in the microbiome can interact not only with the immune system, but also with the endocrine system, to modulate hormone production and behavior (phenotypes) via the vagus nerve, oxytocin reward signaling pathways, and biopterin metabolites.² The gut microbiota’s far-reaching effects on a variety of bodily systems (independent of its effects on the immune system) continue to be discovered and manipulated.
Administering probiotics containing L. reuteri - instead of exogenous oxytocin administration - offers a non-maleficient option (or even beneficient option, given its ability to also benefit the host immune system) as research on the efficacy of exogenous oxytocin emerges. Additionally, the benefits of exogenous oxytocin administration are dependent upon sustained and long-term use, just as transient probiotics are (meaning they do not continue to confer benefits when exogenous supplementation is stopped). Although most probiotics are transient, it may be possible in the near future to design probiotics that colonize the microbiome, eliminating a prolonged dependence on an exogenous supplement. Colonizing probiotics, of course, hold risks that transient probiotics do not.
Regardless, as modern diseases continue to be strongly associated with gut dysbiosis and the resulting inflammation, probiotic therapy holds the potential to completely alter modern medicine and human physiology. For instance, the abundance of L. reuteri in the human intestines has largely decreased in modern humans, likely due to the overuse of antibiotics and our over-sanitized society.⁴ Although it would be difficult to completely modify our germ-fearing culture and derail the food system that kills good bacteria in our guts, medical advancements can allow us to create human microbiomes reminiscent of our Paleolithic ancestors’ microbiomes without sacrificing the conveniences of society, or at least offer probiotics that deliver transiently-beneficial microbes as we await the future of colonizing probiotics.
Microbiome eubiosis is clearly essential to holistic health and the homeostasis of the entire body. Clinical application of microbiome research will continue to become a growing source of interest. Caution should be taken with any new therapy, despite probiotics’ relatively non-maleficient application up to this point.
References
Erdman SE, Poutahidis T. Microbes and oxytocin: Benefits for host physiology and behavior. Cryan JF, Clarke G, editors. Int Rev Neurobiol [Internet]. 2016;131:91–126. Available from: https://www.sciencedirect.com/science/article/pii/S0074774216301180
Dooling SW, Sgritta M, Wang I-C, Duque ALRF, Costa-Mattioli M. The effect of Limosilactobacillus reuteri on social behavior is independent of the adaptive immune system. mSystems [Internet]. 2022 [cited 2023 Mar 25];7(6):e0035822. Available from: https://pubmed.ncbi.nlm.nih.gov/36286493/
Olff M, Frijling JL, Kubzansky LD, Bradley B, Ellenbogen MA, Cardoso C, et al. The role of oxytocin in social bonding, stress regulation and mental health: an update on the moderating effects of context and interindividual differences. Psychoneuroendocrinology [Internet]. 2013;38(9):1883–94. Available from: https://www.sciencedirect.com/science/article/pii/S0306453013002369
Mu Q, Tavella VJ, Luo XM. Role of Lactobacillus reuteri in Human Health and Diseases. Front Microbiol [Internet]. 2018;9:757. Available from: http://dx.doi.org/10.3389/fmicb.2018.00757