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“No, I’m not on my period!”

The controversial science behind menstrual mood swings

About once per month, people with uteruses across the globe experience menstruation, which can have startling effects on the way we think and feel. The Mayo Clinic notes that symptoms of premenstrual syndrome (PMS) include mood swings, irritability, and depression. Those who have experienced menstruation often feel confused when reacting to situations differently from how they normally do. It is estimated that for 3 to 9 per cent of the female population, the symptoms of PMS become severe enough to interfere with work, school, social activities, or relationships, causing functional impairment and harm to one’s mental health. The severe form of PMS is called premenstrual dysphoric disorder (PMDD), and it is classified as a mental disorder in the Diagnostic and Statistical Manual of Mental Disorders (DSM). For people who experience PMDD, PMS symptoms stop being just a monthly inconvenience and become a real burden.

But how is it that normal reproductive function can have a consequence on mental health? Is there a clear mechanism that explains how hormones may impact nervous system functioning? Or is it more a question of a biased interpretation of normal bodily processes, the bias arising from physical discomfort and reinforced by the negative view society has on menstruation?

Do PMS and menstruation really affect our brains?

One widely held hypothesis focuses on possible effects of hormones on the nervous system, though it is not very well supported. This hypothesis suggests that severe PMS may be the result of altered activity or sensitivity of certain neurotransmitter systems, caused by changes in steroid hormone concentration.

Evidence cited by proponents of this hypothesis comes from mood changes related to pregnancy, delivery, menopause, and other physiological states in which hormones are shifting dramatically. Postpartum depression and the increased onset of anxiety disorders after menopause would act as examples of hormonal changes that have negative consequences for mental health.

There are issues with this hypothesis, however. We know that brain activity generates and directs the production of all hormones through the neuroendocrine system. This interaction between the nervous system – the brain – and the endocrine system involves different hormone-secreting glands in our bodies. However, this does not explain in any way how the balance between steroid hormones such as estrogen, progesterone, and testosterone can affect neurotransmitter function. So far, there is no evidence of clear molecular or cellular mechanisms to explain a hormonal influence on neurotransmission, nor a clear model of which hormonal profile contributes the most to positive or negative moods.

As a society, we should consider changing the way we view the normal female reproductive function, dropping the misleading notion that it is a “risk factor” for instability, anxiety, depression, and lack of mental control.

Scientists that side with the biological susceptibility hypothesis also claim that it is open to non-biological factors, explaining that the neuroendocrine process related to female reproduction is also vulnerable to changes in psychosocial, environmental, and physiological spheres. But the question remains: why are only female reproductive hormones – and not any of the other axes of the endocrine system – causing these impacts on emotional states?

The bias in our approach to PMS and menstruation

To assess the strength of scientific evidence in support of a well-defined PMS, researchers at the University of Toronto conducted a literature review in 2012 that examined more than 47 scientific studies on the daily reported moods in people who do not look for medical assistance to solve their period-related issues. Surprisingly, the majority of subjects did not regularly experience premenstrual negative moods. Adding to a previous study done by the same group in the same year that failed to find a clear relation between mood and specific hormone concentrations in saliva, blood, and urine, it may well be that the evidence we used to define the existence of mental health disturbances in PMS as a universal phenomenon could have been biased to begin with.

There are several factors that may have lead to bias in studies related to mental health and PMS. First, most of the information gathered about the syndrome comes from those who seek help and do not represent the general population of people who have periods. Also, the more than sixty instruments used to gather information on subject’s moods during the menstrual cycle ask mainly about experiences such as depression, anxiety, and irritability, placing much more emphasis on the negative experiences and thus limiting a complete description of premenstrual mood experiences.

The majority of subjects did not regularly experience premenstrual negative moods.

Interestingly, in 1994, a research group led by Joan Chrisler at Connecticut College created the Menstrual Joy Questionnaire (MJQ) to study how positive moods varied with the menstrual cycle in an attempt to shift the focus from negative phenomena only. Among the forty participants that responded to the questionnaire, about 75 per cent reacted with incredulity, surprise, or thought that the title was ironic – as if, to them, it was impossible to find joy in such a thing.

An interesting point to discuss is the definition that Antonio Damasio, a professor of neuroscience at the University of Southern California, gives for emotions. He explains that feelings arise from a conscious interpretation of purely physical signals of the body reacting to external and internal stimuli. In this case, negative emotions during both PMS and menstruation could arise from the physical discomfort caused by symptoms like bloating, water retention, breast tenderness, and menstrual cramps. To this is added the fact that menstruation is generally looked at in society as negative, even disgusting.

Overall, we find that the evidence for the biological susceptibility hypothesis is not convincing enough to explain a consistent change in neurotransmitters that repeats itself period after period, nor to believe that women’s negative mental states are largely determined by their hormones. However, whether it’s in the media, in the way we talk to each other, or in the way parents teach their children about menstruation, we as a society keep reinforcing this idea by associating the anger or sadness experienced during the menstrual period with hormones, or assuming women’s judgement may be blurred by PMS. Studies on those who do not have PMDD don’t show any consistent patterns of dysfunction due to negative premenstrual moods. So, with 75 per cent of the female population experiencing PMS, and without any evidence of an aberrant function of the hormonal system, should we keep thinking of it as a syndrome or disease? Or, is the idea that it is a well-established disorder misleadingly reinforcing our negative perception of normal body processes? It is true that, for those with PMDD, the symptoms associated with the last phase of the cycle may be a cause of distress and may require medical attention. When people do experience mental and physical health issues as a result of PMDD, it is important we take this seriously, and not write it off as, “Oh, it’s just because of your period, suck it up.” But, among those who have periods and do not suffer from PMDD, menstruation need not continue to be seen as a negative phenomenon that could lead to neurological impairment, such as irrational emotionality, as the science simply does not support this.

We cannot deny the highly negative images of menstrual function that still prevail, or the negative side effects of this experience. I have personally experienced discomfort and mood changes at the onset of my period on many occasions. However, given the evidence, I realize the source of these experiences may not be as clear or well-defined as I thought it was. As a society, we should consider changing the way we view the normal female reproductive function, dropping the misleading notion that it is a “risk factor” for instability, anxiety, depression, and lack of mental control. This may not only help people endure their mood changes during their cycle as something normal, but may be the first step toward avoiding the long prevailing negative image of female sexual physiology.