What can modify a woman's physiology

Having looked at in the last few blogs at the normal menstrual cycle in detail in terms of the major hormonal changes that occur and how it affects a women's physiology, Let's now look at some commonly experienced situations that will change a woman's physiology from that of the normal menstrual cycle.

We now know the three primary hormones which impact on a woman's overall physiology are estrogen, progesterone and testosterone. Each has its own distinct effects and, when one or the other is relatively dominant in a woman's body, it generally results in a fairly similar physiology. So regardless of the specific hormonal modifier present, two women with an estrogen-like, progesterone- like or androgen-like physiology will be considered to have a similar physiology.


While there is no truly "normal' menstrual cycle, in that the variation between two women (or within the same woman) can be extremely large, it is still possible for the cycle to become extremely disrupted. While there are less severe disruptions I will mainly focus on amenorrhea and oligomenorrhea here.

Amenorrhea refers to the absence of a menstrual cycle and is defined clinically as a lack of menstruation for 90 days or more with less than three total cycles in a year (some women will not menstruate for extended lengths of time). Strictly speaking, amenorrhea can occur under many different situations. This can include a woman who has begun to menstruate at all (called primary amenorrhea), pregnancy (where menstruation stops due to not being needed) and birth control (which deliberately shuts off the normal cycle although some bleeding may still occur). There can be numerous medical causes for amenorrhea but none of these represent the type of amenorrhea that I will discus in this blog.

Rather, I will focus only on Functional Hypothalamic Amenorrhea (FHA). As the name suggests, FHA originates in the hypothalamus, which will shut down the menstrual cycle under certain circumstances. These tend to be stress related including the stress of dieting, the stress of exercise, mental stress or some combination of the three. Physiologically, in amenorrhea, estrogen drops to about 33% of normal levels and progesterone drops to roughly 10% of normal. The normal cyclical changes are also lost and hormonal levels of both are effectively a flat line. The release of LH and FSH, which I described briefly in the last blog, also disappears such that the follicle never matures or implants, the corpus luteum doesn't develop and there is no uterine lining to shed (hence the lack of bleeding). When amenorrhea develops, a woman's physiology changes enormously.


Oligomenorrhea refers to an infrequent or delayed menstrual cycle and is defined clinically as a cycle that only occurs every 35-90 days (recall that the normal menstrual cycle occurs within 24-32 days). In contrast to amenorrhea where a woman's primary hormones drop to low levels and show no cyclical changes, in oligomenorrhea those hormones are lowered but are still changing. On some days hormone levels may be identical to the normal menstrual cycle but on others their levels will be random. Like amenorrhea, oligomenorrhea can occur for many reasons.

This includes some types of birth control (where light bleeding may occur) and a variety of medical conditions (including PCOS, discussed below).

There are two types of oligomenorrhea. The first is part of the continuum of adaptations to dieting that can lead to amenorrhea. While all women were originally thought to have this type of oligomenorrhea although it's now known that there is a subgroup of women who are oligomenorrheic due to elevated androgen/testosterone levels.