A monthly defence

14/11/1993
Down To Earth

A monthly defence DREAMS are often the crucibles of new ideas. Remember Kekule dreaming up the ringed benzene structure. Margie Profet, too, had one such dream in 1988. She dreamt that menstrual bleeding was a broom that swept away sperm-borne offending microbes from the uterus.

Now she has made her dream public, contesting the orthodox view that menstruation is merely the body's way of getting rid of the built-up uterine lining when conception does not occur. By subscribing to this view, physicians may have unwittingly sabotaged a woman's natural defences with inappropriate treatment in cases of uterine infection.

Expensive exercise
Profet, an evolutionary biologist from the University of California at Berkeley, says the monthly bleeding is an expensive exercise that drains off the body's precious iron reserves and also takes away from fertility time. Therefore, she argues, it would have failed as an evolutionary trait unless it also performed some adaptive function.

That function, according to her, is to prevent sperm-borne microbes, such as streptococcus, from taking hold in the uterus. Profet says menstrual blood is expressly designed for this purpose, with its rich supply of disease-fighting immune cells. She notes that women with uterine infections, or the chronic inflammation an intrauterine device normally causes, respond by bleeding profusely. Her theory implies that physicians will now have to routinely consider infections as the cause of unexplained vaginal bleeding.

However, some biologists are not convinced. Says University of Michigan anthropologist Beverly Strassman, "Over most of human evolutionary history, women weren't menstruating very often" because they were usually either pregnant or breast-feeding, which suppresses menstruation.

Furthermore, epidemiologist John S Moran of the Centers for Disease Control and Prevention points out that sperm is not a major culprit in spreading disease. A sore on a man's penis or infected secretions from his urethra can easily transmit an infection even without ejaculation. Some supporters of Profet's hypothesis also say menstruation may have additional functions: signalling that a woman is fertile, for instance.

Another problem with Profet's theory is that sexually transmitted diseases are common in menstruating women and some of them, notably gonorrhoea, actually cause more complications during menstruation. "We are in a co-evolutionary race with many other organisms," responds Profet. "Sometimes they win, but without menstruation there would be much more infection."

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