Women who feel grouchy before getting their periods shouldn't blame it on their hormones directly, according to researchers at the University of Toronto.

Women's menstrual cycles are mythologized as a time of the month of low mood and irrationality.

But when researchers at the University of Toronto looked at published medical research on the topic, the methods used were so varied that they couldn't do a proper analysis.

The researchers did not discount that women may experience physical symptoms, such as bloating and cramps, during the pre-menstrual phase of the cycle. (iStock)

"Taken together, these studies failed to provide clear evidence in support of the existence of a specific premenstrual negative mood syndrome in the general population," Gillian Einstein, a professor in the psychology department at the University of Toronto and her co-authors concluded in the journal Gender Medicine.

"This puzzlingly widespread belief needs challenging, as it perpetuates negative concepts linking female reproduction with negative emotionality."

Einstein's team also did their own study, measuring hormone levels in the urine of 14 women aged 18 to 40 in the Greater Toronto Area who weren't seeking medical attention for menstrual symptoms.

The women also used a smartphone to log their daily moods, both positive and negative, over 1½ menstrual cycles.

"Our major finding is that, with a few exceptions, neither absolute hormone levels nor menstrual cycle phase as determined by hormone levels played a significant role in daily mood of this group of women," the researchers concluded.

"Rather, perceived stress and physical health were the strongest contributors to statistical models of daily positive and negative mood."

Factors like stress, lack of social support, money worries and physical ailments also can impact a woman's mood, Einstein said.

Other studies using different methods also found inconsistent, minimal or non-existent influences of the hormones estrogen and progestagens on daily mood in healthy women, they said.

Dr. Jerilynn Prior is a professor of endocrinology and metabolism at the University of British Columbia in Vancouver who studies menstrual cycles.

Prior followed 62 women over a year, and couldn't find a PMS pattern, either, in younger women.

"It's great to see this confirmation that there isn't any such thing as this psychiatric illness that all women get in the few days before their flow, but that it is a real thing for perimenopausal women," Prior said.

Extreme cases rare

The researchers did not look at premenstrual dysphoric disorder (PMDD), a clinical mood disorder linked with the menstrual cycle that is characterized by severe physical and behavioural symptoms in the second half of the menstrual cycle.

Psychiatrist Dr. Diane Meschino, director of a reproductive mental health at Women's College Hospital in Toronto, said that by and large, she agrees with the findings. But in her practice, she does see women with premenstrual disorder that include extreme moodiness.

Such moodiness and depression are rare, Meschino said, but they do exist and are documented in diaries her patients keep of their symptoms. Pre-menstrual exacerbation of chronic depression is also rare. It's all a reflection of how enormously complex mood is, she said.

The researchers also did not discount that women may experience physical symptoms, such as bloating and cramps, during the pre-menstrual phase of the cycle.

Abby Lippman, professor emerita in the department of epidemiology, biostatics and occupational health at McGill University in Montreal, said the U of T team researched a difficult topic given that PMS is rife with preconceived notions.

"Challenging assumptions is essential in exploring the givens associated too easily by too many with regard to women's health and the U of T folks show one way of doing this," Lippman said.

In downtown Toronto, news of the findings was greeted with skepticism.

"Any woman would know that there is PMS," said one woman, pointing to women feeling upset and annoyed before their period.

Another woman said she appreciates how pain could affect women psychologically.

With files from CBC's Kelly Crowe