Toronto, March 2 (IANS): Women who work in night shifts, even occasionally, are at an increased risk of early menopause, which can heighten the possibility of developing cardiovascular disease, osteoporosis and memory problems, finds a new study.

The study showed women who had done continued night shifts for 20 months or more in the preceding two years had a nine per cent increased risk of early menopause, the Daily Mail reported. If they had done rotating night shifts for more than 20 years, the risk rose to 73 per cent.

"For women who went through menopause before the age of 45, shift work seemed to be particularly important. This could be due to disruption of their circadian rhythms, stress or fatigue, although more research is needed," lead author David Stock, from the University of Dalhousie in Canada, was quoted as saying.

An early menopause could also come from the stress of working late at night, as stress hormones are believed to disrupt sex hormones like oestrogen. This could also increase the chance that a woman stops ovulating, according to the study published in the journal Human Reproduction.

Previous evidence suggests working in 'high-strain' jobs and those with 'difficult schedules' is linked to earlier menopause.

For the study, the team studied more than 80,000 nurses who worked at least in the night shifts in a month for over 22 years in addition to day and evening shifts.