Circadian rhythm disruptions linked to infertility: Study

Washington: Disruptions to the circadian rhythm or the body`s biological clock may cause fertility problems, a new study has claimed.

A team at Northwestern University in the US disrupted the circadian rhythms of female mice for five to six days after they mated. One group of 18 mice got an extra six hours of light, while another 18 mice lost daylight.
By the end of the experiment, only half of the mice with extra daylight had litters and mice that lost daylight fared worse -- only 20 per cent gave birth. But 90 per cent of a control group exposed to a steady 12 hours of daylight gave birth, found the study published in the journal PLoS ONE.

Mammals, and even trees, are known to synchronise their internal clocks, which control metabolism and other functions, to cues of night and day. Experts in fertility and circadian rhythms agreed the mouse experiments showed a strong connection between the mouse`s internal clock and pregnancy.

However, critics expressed doubts over the study, saying stress may play a role in women`s fertility problem.

Keith Summa, who led the study, said the details may be different across species, but what they found in mice will be relevant to humans, LiveScience reported.

Summa and his team pointed to surveys showing that nurses who work night shifts experience a high rate of irregular menstrual periods and other "adverse pregnancy outcomes."

"I think the idea that`s really interesting is that [the circadian] timing of the uterus is an important component to either establishing or sustaining early pregnancy," Suma said.

But, Neil Goodman from the American Association of Clinical Endocrinologists said he doubts there`s such a link. "I wouldn`t call the fertility issues in women circadian," he said."Every woman knows that any kind of stress can interrupt her periods,"

Moreover, Goodman said, he doesn`t trust mice as a model for human fertility. Mice menstruate on a different cycle and respond to different hormonal cues than humans do. (More) PTI

Yet researchers of circadian rhythms said much remains unknown about internal clocks, health and regulatory systems.

"Many, many more things are being connected to our sleep cycles -- even diabetes and heart disease," said Fred Davis, an expert in circadian rhythms and developmental biology at Northeastern University in Boston.

Megan Mahoney, a chronobiology professor at University of Illinois, added that links between poor sleep and cancer have been found in both mouse and human studies.

The study "may be in mice, but it is the first step in finding the mechanisms that cause that problem," Mahoney said.