If the level of oestrogen declines in the vagina, bladder and pelvic floor, this in turn affects the growth of vaginal epithelial cells and the availability of glycogen (a stored form of glucose is made up of many connected glucose molecules and is called glycogen). Because glycogen is the main nutritional source for lactobacillus, the beneficial bacteria in the vagina, this results in lower production of lactic acid which keeps the vaginal PH acidic and creates a higher more alkaline vaginal PH in which lactobacilli strains cannot survive. This leads to the level of lactobacilli in the vagina dramatically decreasing alongside the production of lactic acid and hydrogen peroxide.
When the level of lactobacilli is disrupted and the vaginal flora becomes imbalanced, the risk of developing an infection is increased. If the vagina is not acidic enough, then fungi such as candida, vaginal infections such as bacterial vaginosis (BV), vaginitis and ‘bad’ bacteria such as coliforms, enterobacter, gardnerella, mycoplasma, streptococci and staphylococci are able to reproduce more than they usually would.
Low oestrogen can also affect the structure of the delicate mucous membranes, or muscles, that line many parts of the body, including the urinary tract, making infections more likely. Thinning of the vaginal and vulval mucosal lining also affects the mucosal wall of the bladder allowing bacterial permeability – in other words it becomes easier for bacteria to become established on or within the cells of the bladder and vaginal walls. Further, the walls of the vagina, urethra and bladder rely on oestrogen as one way to stay toned and able to manage the flow of urine from the bladder. With less oestrogen, these organs lose tone and some degree of function.
Too much synthetic progesterone weakens the lining of the bladder, urethra, and vagina leaving them more susceptible to injury and inflammation and can cause urogenital/vaginal/urethral atrophy because oestrogen levels cannot compensate and help to rebuild healthy tissue.
High levels of progesterone can also cause frequent urination as progesterone acts like a diuretic. The sacral nerve which controls the pelvis and its organs is full of oestrogen receptors. Research published in The International Urogynecology Journal in 1993 showed a change in hormone levels, in particular that of progesterone, may affect the excitability of the nerves and make you feel like you have to urinate more frequently. This may also be the reason for frequent urination during the second half of the menstrual cycle as progesterone levels are higher than those of oestrogen.
A study published in Science Translational Medicine in 2013 noted that oestrogen also encourages production of natural antimicrobial substances in the bladder. The hormone also makes the epithelium of the bladder wall stronger by closing the gaps between cells that line the bladder wall. They also noted that by “gluing” together the cells of the bladder wall, it helps to prevent bacteria from penetrating to the deeper layers of the wall and may help prevent too many cells from shedding from the top layers of the bladder wall thus preventing exposure of the deeper bladder wall tissues to bacteria.