Breast cancer: Women who are early risers have lower risk

Maricruz Casares
Noviembre 8, 2018

If a woman regularly wakes up early in the morning, she has up to a 48 percent lower risk of developing breast cancer, according to a study in England.

The research, which is being presented at the NCRI Cancer Conference in Glasgow, also found that breast cancer risk increased by 20 per cent for every hour a women slept beyond the recommended amount of 7 to 8 hours a night.

Led by Dr Rebecca Richmond at the University of Bristol, UK, along with the University of Manchester, the University of Exeter, and USA and Norwegian researchers, the large-scale study looked at data from taken from 409,166 women to investigate how a person's preference for mornings or evenings as well as their sleep habits may contribute to the development of breast cancer.

"The team used a method called "'Mendelian randomization", which uses genetic variants linked to potential risk factors (in this case, circadian rhythm) to determine whether or not there is a causal relationship between the risk factor and a particular disease (in this case, breast cancer).

However, Dr Richmond pointed out that the possible protective effect of being a morning person on breast cancer risk was in keeping with previous research showing that working night shifts and "light-at-night" exposure increased the risk of breast cancer.

Women have a one in eight chance of developing breast cancer and there are about 11,500 deaths from the disease annually in Britain.

Age and family history are some of the main risk factors for breast cancer.

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"The authors do not show any biological mechanism by which sleep timing preference could influence breast cancer risk".

Because these bits of DNA are set at birth and are not linked to other known causes of cancer, like obesity, it means the researchers are reasonably confident body clocks are involved in cancer.

There is good news if you are a morning person.

The study was funded by Cancer Research UK and the Medical Research Council. Does the body clock affect hormone levels to alter cancer risk, or the immune system, or metabolism? "I wouldn't support that women should get up earlier to reduce risk of breast cancer".

"We know that sleep is important generally for health", said Richmond.

The findings have been published on researchers' website bioRxiv but have not yet gone through scientific peer review.

Dipender Gill, of Imperial College London, said: "Although informative and interesting, this study alone does not warrant any action other than further investigation - people should not be changing their sleep patterns based on the evidence presented here".

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