Role of phytoestrogens on expression of oxytocin and oxytocin receptors and resulting behavioral changes in humans

Abstract

Soy based products are growing in popularity in food supplementation, and a larger population of the world is consuming soy on a regular basis. Soy contains phytoestrogens, plant based mimics of the hormone estrogen. Estrogen has many functions in humans, but one relatively unexplored function is its ability to regulate the levels of the hormone oxytocin (OT) and its receptor (OTR) in the brain. OT is a hormone traditionally known for its role in birth, but recently has been as a key regulator in many different behaviors. These behaviors that OT may affect include increased maternal behaviors, increased sexual behaviors, increased social interactions, increased trust, decreased anxiety, and increased potential for pair bonding. Key phytoestrogens found in soy are of the isoflavone family, and genistein and diadzein are the main two isoflavones that have been shown to exert physiologic effects when ingested by binding to estrogen receptors in the brain. The isoflavones can be estrogen agonists or estrogen antagonists, based on the preexisting, endogenous levels of estrogen in the individual. For men and postmenopausal women, it is believed that ingesting soy can cause an increase in production of OT and OTR, resulting in an increased in OT driven behaviors. For premenopausal women, there is a high endogenous level of estrogen present, so the ingested soy can cause a decrease in production of OT and OTR in the brain, resulting in a decrease in OT driven behaviors. While there is strong evidence to suggest that this may in fact occur in humans, more human based studies, rather than animal models, must be conducted to further verify and validate this hypothesis. An important area yet unexplored is the onset and duration of these OT driven behaviors. It is unclear if these are transient, or more long lasting effects, and future studies must be done to answer this question. This area of research is certainly more relevant as soy based diets are becoming more common; moving forward additional research is needed to determine the extent of oxytocin's ability to alter behaviors in individuals in a significant way.