A recent study suggests that women who like to wake up early every day may be less likely to develop breast cancer than others.
While previous studies have linked inconsistent sleep schedules and getting too much rest to an increased risk of breast cancer, researchers haven't looked as often at how much women's wake-up time might impact this risk, researchers note in the British Medical Journal.
For the current analysis, researchers analyzed genetic variants associated with three sleep traits: sleep duration, insomnia, and a so-called morning or evening chronotype, referring to early or late risers. They looked at data on over 400,000 women in two national studies: one focused on the biological data and the other on breast cancer.
The biological data study found that among every 100 women who were early risers, there was one fewer case of breast cancer. But there wasn't a clear connection between breast cancer and sleep duration or insomnia.
In the study focusing on breast cancer, the findings also showed that women who woke up early had a lower risk of breast cancer. In addition, it found that sleeping more than the recommended 7 to 8 hours a night was associated an increased risk - 19% for every extra hour.
Rebecca Richmond, lead study author and a researcher at the University of Bristol in the UK said: "The findings in our study are consistent with previous research highlighting a role for night shift work in the development of breast cancer."
"One particular mechanism which might explain the link, known as the 'light-at-night' hypothesis, involves the suppression of melatonin levels in women exposed to artificial night at light, which in turn influences various hormonal pathways which might increase risk of breast cancer," she added.
But women shouldn't rush to reset their alarm clocks to lower their breast cancer risk, she noted.
"Our main findings were based on women's reported morning or evening preference, rather than actually whether they get up earlier or later in the day. Results might differ for women from other racial and ethnic groups too," Richmond concluded.
