Women who wake up early have almost half the risk of developing breast cancer compared to night owls who are active during the evening hours and go to bed late, according to a recent UK study.

The study was conducted at the University of Bristol and appears in the British Medical Journal. The authors had earlier presented the findings at the National Cancer Research Institute Conference (NCRI) in Glasgow.

Aim of the Study

Previous research indicates a link between working night shift and increased breast cancer risk, believed to be caused by a disruption in sleep patterns, exposure to the bright environment, and other lifestyle factors. However, not much data is available on the potential impact of sleep habits and breast cancer risk.

The study team set out to determine whether certain sleep traits could influence breast cancer risk.

• The study employed a technique Mendelian randomization, and analyzed genetic variants associated with three specific sleep traits namely morning or evening chronotype (when a person is most active), duration of sleep, and insomnia.
• An association noted during a Mendelian randomization study increases the chances of a causal relationship and reduces the scope for erroneous conclusions caused by confounding factors.

Analyzing Risk of Breast Cancer in Larks Vs Owls

• The trial analyzed data from about 400,000 women who had provided their genetic information either in the UK Biobank or the Breast Cancer Association Consortium (BCAC) study.
• The study team looked at 450 genetic markers related to sleep, including "chronotype" (when a person is most active), sleep duration, and insomnia
• Using Mendelian randomization method, the team were able to study breast cancer risk independent of confounding factors such as smoking and alcohol
• The findings of the analysis found that morning preference was associated with a slightly lesser risk of breast cancer (one less woman per 100) than evening preference, which translates to a 48-50% lower risk in morning larks
• Analysis of BCAC also found that women who slept longer than the advised seven to eight hours per night had a higher risk of developing breast cancer by 20% for every additional hour. However, analysis of UK Biobank data revealed that there was little evidence for a link with both sleep duration and insomnia

Dr. Rebecca Richmond, lead scientist from the University of Bristol, "The findings of a protective effect of morning preference on breast cancer risk in our study are consistent with previous research highlighting a role for night shift work and exposure to "light-at-night" as risk factors for breast cancer."

Potential Merits & Demerits

• According to the authors, possible demerits include that the study relied partly on self-reported sleep measures and comprised only women of European ancestry, and so the findings may not apply to other races
• The merits are that the scientists used several methods to analyze information from two highly respected resources, and accounted for other possible and established risk factors. The results were also the same after additional sensitivity analyses

Scope of the Study

• Further studies will be necessary to unearth potential reasons between disruption in sleep behavior and breast cancer risk since other factors like work and family influence our sleeping and waking time, and the authors feel this mismatch may account for some additional risk
• Although cancer risk may be set in the genes, changing our sleep behavior can help modify the risk
• The findings of the study suggesting that matching our biological clocks to our occupational clocks may help reduce disease risk

In summary, morning persons have a lower risk of breast cancer in comparison to late risers and these findings suggest that changing sleep behavior can improve health and reduce the risk of cancer or other chronic diseases.

‘Evening persons or night owls have a gene mutation resulting in their body clock to lag behind, making them go to bed late and wake up later than usual in the morning. New study suggests that this gene mutation may increase the risk of breast cancer, making women who are night owls more prone to breast cancer.’
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