We know that sleep is important generally for health
Turns out, women who are naturally early risers were found to have a lower risk of developing breast cancer. According to a study, one in 100 women who considered themselves morning people developed breast cancer, compared with two in every 100 women who called themselves evening people. Cancer risks associated with a person's body clock and sleep patterns have been reported in previous researches as well as any genetic factors underlying this.
Self-reported preferences for mornings or evenings (by their own definition of that preference) were recorded in more than 180,000 women, led by Dr. Rebecca Richmond, a researcher.
The team of researchers also analysed genetic variants linked to whether someone is a morning or night person in more than 220,000 women to find out if these could help provide a causal link to breast cancer.
Women who are naturally early risers were found to have a lower risk of developing breast cancer.
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This type of statistical model, called Mendelian randomisation, showed that people whose genes made them more likely to be early risers were less likely to develop breast cancer by as much as 48 per cent, as shown from the 220,000 participants in the study.
The second analysis, using self-reported data on sleep from 180,000 participants, showed a similar trend of early rising women having a 40 per cent lower risk of breast cancer. The variation is due to technical differences, stated Richmond.
Women who self-reported sleeping more than the average seven to eight hours per night were also found to have a slightly increased risk of breast cancer, of 20 percent per extra hour slept, according to the team's Mendelian randomisation analysis.
But the team pointed out that many factors are involved in a person developing breast cancer and that these numbers are not an absolute risk. Also, the findings cannot be applied across populations as the majority of women included were of European ancestry.
"Sleep is likely to be an important risk factor for breast cancer, but it isn't as large as other well-established risk factors like BMI or alcohol," said Richmond.
"We know that sleep is important generally for health," said Richmond. "These findings have potential policy implications for influencing sleep habits of the general population in order to improve health and reduce the risk of breast cancer among women."