Shift work could negatively affect women more than men, suggests a British study comparing performance after 28-hour schedules that delayed sleep-wake cycles.

Scientists at the Surrey Sleep Research Centre found shifted sleep-wake cycles affect men’s and women’s abilities to function differently.

The researchers put 16 men and 18 women on 28-hour days in a controlled sleep lab, diverting them from the typical 24-hour circadian rhythm. They were tested every three hours (while awake) on attention, motor control and memory and asked to self-report their mood and wakefulness.

The researchers measured the volunteers’ electrical brain activity during sleep cycles.

The objective measures showed women performed worse during the early morning, when a shift worker might be completing work. The researchers called out nursing as one of several professions that could be affected.

In more bad news for female nurses, disruption to biological rhythms slightly increases the risk of coronary heart disease.

A different study, from Brigham and Women’s Hospital and Harvard Medical School, tracked nearly 190,000 women over 24 years using the Nurses’ Health Studies.

Those who worked rotating shifts were more likely to have heart disease the longer they kept at it. The risk appeared to decrease after quitting shift work.