Breast feeding may alter other women's cycles

Breast feeding mothers may affect the length of other women's menstrual cycles, claims Professor Martha McClintock of the University of Chicago. She found that lactating women can alter the cycle length of other women, perhaps through pheromones, chemical signals emitted by the body.

The researchers placed absorbent pads in the nursing bras and armpits of breastfeeding women, and then asked volunteers to rub the pads under their noses every day for about two months. During the experiment, short cycles became shorter and long cycles became significantly longer. 'Some kind of chemosignal from the breastfeeding environment is disrupting their cycles' said Natasha Spencer, one of the scientists involved.

Professor McClintock, who showed two years ago that women living together tend to synchronise their menstrual cycles, now wants to find out if the timing of pregnancies can be synchronised by a chemical signal. But Professor Bill Hansson, of the pheromone research group at Lund University, Sweden, says more evidence would be needed of the effect, adding: 'This could be feasible but you need to be extremely cautious.'