Is PMT a myth?

Premenstrual tension "may be all in the mind", the Daily Mail reported today.

This story is based on research that looked at whether there is any good evidence to support the widely held view that women suffer negative moods, such as irritability or anxiety during the premenstrual phase of the menstrual cycle.

This is commonly referred to as premenstrual syndrome (PMS), which covers a range of symptoms thought to occur in the two weeks preceding menstruation. Symptoms include fluid retention, breast tenderness, mood swings, feeling irritable and loss of interest in sex. The exact cause is not fully understood, but it is thought to be linked to changing levels of hormones.

Researchers say they found that only about one in six studies showed an association between negative mood and the premenstrual phase. The authors argue that the “puzzlingly widespread belief” that women have mood swings before their periods needs challenging.

As the authors rightly point out, the traditional belief that women’s moods are dictated by their hormones can be used in a negative way, to label women as governed by emotions. Mood swings can be caused by many factors, including stress, work and relationships. 

The conclusions of this review should be viewed with caution as they are dependent on the quality of the studies included. Many of these studies were very small – some had fewer than 10 participants – which means they lacked the power to detect differences in mood at different times of the menstrual cycle. Also, the researchers were unable to summarise the results in a meta-analysis because the studies varied so widely in the methods they used.

Due to the lack of statistical rigour, this study seems more of an opinion piece than an example of significant medical research.

Where did the story come from?

The study was carried out by researchers from the University of Otago, Wellington in New Zealand and Dalhousie University, the University of Toronto, the Hospital for Sick Children and the University Health Network, all in Canada. It was partly funded by the Canadian Institutes of Health Research. The study was published in the peer-reviewed journal Gender Medicine.

The Mail’s coverage was fair, if uncritical of the research. The Daily Telegraph’s headline claiming that premenstrual syndrome is a myth was misleading since PMS is associated with physical as well as emotional symptoms. In this study the researchers only looked at changes in mood and not physical symptoms such as breast tenderness. Neither paper included any comments from independent experts.

What kind of research was this?

This was a systematic review that looked at the evidence to support the view that the premenstrual phase causes negative mood in women.

The authors say that, historically, the menstrual cycle has been the focus of “myth and misinformation”, leading to ideas that constrain women’s activities.

They argue that there is confusion as to whether PMS refers to mood swings alone or physical symptoms too, and also uncertainty as to its timing – whether it ends promptly with the onset of the period or some days later.

Although this was a systematic review, it did not include a meta-analysis, which is a statistical technique for combining the results of different studies to arrive at an overall summary measure of any effect.

What did the research involve?

The researchers conducted a search of two databases, as well as article bibliographies, for all articles describing human studies of mood and emotions recorded during the menstrual cycle.

Only studies with a control group were included since, as the researchers point out, to find out if the premenstrual phase is linked with negative mood, studies have to compare moods during other phases of the menstrual cycle.

They also only included prospective studies (studies in which women were recruited first and then asked to report their moods during a subsequent menstrual cycle, rather than reporting on mood during past cycles). They also only included studies that provided daily data on mood for a minimum of one complete menstrual cycle. They excluded studies of women seeking medical help for mood problems.

Researchers also looked at whether the sample sizes were adequate and conducted a further survey of the 41 studies that were considered adequately powered (those in which the sample sizes were large enough to give weight to the results).

What were the basic results?

The authors found 47 articles that met their criteria. Sample sizes in the studies ranged from six to 900, with an average size of about 92. The main findings were that:

• 18 (38.3%) studies found no association between mood and any phase of the menstrual cycle
• 18 found an association between negative mood and the premenstrual phase, but also negative mood at other points of the cycle
• seven (14.9%) found an association between negative mood and the premenstrual phase
• the remaining four studies (8.5%) showed an association between negative mood and a non-premenstrual phase

How did the researchers interpret the results?

The authors say that, taken together, these studies fail to provide clear evidence in support of the existence of a specific premenstrual negative mood syndrome in the general female population. They say: “This puzzlingly widespread belief needs challenging, as it perpetuates negative concepts linking female reproduction with negative emotionality”.

Conclusion

This systematic review covers an important topic but its conclusions should be viewed with caution. As the authors point out, the quality of the studies included varies, with some studies being too small to be adequately powered, meaning they would be unlikely to show an effect. In some studies, women knew the focus of the research, which may have influenced their responses. Other potential problems with this review include the fact that:

• more than half the studies covered only one menstrual period for all participants 
• more than a third used university or nursing school students for their sample, so they cannot be said to represent the wider female population 
• in more than half of the studies women knew what the aim of the study was
• the methodology used by the authors in assessing quality is unclear
• the studies used different methods for assessing women’s moods, which would make combining the results difficult
• the results were not combined, nor did the researchers carry out a meta-analysis of their findings
• in their descriptive results presentation, the researchers only gave the proportion of studies showing an association (or not) without describing the strength of the link

The issue of whether, and how, the menstrual cycle affects mood is an important topic that requires further study. There is no cure for the symptoms of PMS but lifestyle changes and some medical treatments can help women manage the symptoms.

The researchers raise some interesting questions about whether cultural attitudes contribute to women’s response to menstruation. For example, until the latter part of the twentieth century menstruation was still very much a taboo subject in Western society, which may have contributed to negative feelings about menstruation and triggered mood changes in women at the time of their period. However, these questions may be better investigated using sociological and anthropological rather than medical research.