Owl types have higher breast cancer risk than lark types

Night owls, who stay up late, have higher risk of breast cancer than the larks, who like to get up early, a research published recently in journal The BMJ says.

In a study involving 180,216 women in the UK Biobank study and 228,951 women in the Breast Cancer Association Consortium (BCAC), a team of researchers found that morning preference was associated with a slightly lower risk of breast cancer (one less woman per 100) than evening preference. However, there was little evidence for an association with sleep duration and insomnia symptoms. But the researchers say that the extent of effect is likely to be smaller than that of other known risk factors for breast cancer, such as BMI and alcohol intake.

“In 2007 the World Health Organization’s International Agency for Research on Cancer classified shift work that involves circadian disruption as being probably carcinogenic to humans. Disturbed sleep, exposure to light at night, and exposure to other lifestyle factors have been proposed as possible underlying mechanisms. Although much of the literature on breast cancer risk has focused on the potentially adverse effects of night shift work and exposure to light at night, less investigation has been done into the potential adverse effects of sleep disruption and traits such as chronotype (morning or evening preference), sleep duration, and insomnia,” the study says.

The study concluded that the findings showed consistent evidence for a protective effect of morning preference and suggestive evidence for an adverse effect of increased sleep duration on breast cancer risk. However, the researchers say whether it is the actual behaviour that poses the health risk or the preference for morning versus evening requires further evaluation.

Experts have warned that the study does not suggest a change in sleeping pattern would reduce the risk of breast cancer. “What they suggest is that it appears that the risk of breast cancer is associated with a genetic (thus not modifiable) trait that is in itself associated with a “morning” or “night” preference – what we call ‘larks’ and ‘owls’. This being a correlation, it is likely that these genetic traits are linked to breast cancer risk though a different (and more precise) mechanism,” Dr Luca Magnani, Senior Research Fellow in the Department of Surgery & Cancer at Imperial College London, told Science Media Centre.

Reacting to the study, another expert, Prof Chris Bunce, Professor of Translational Cancer Biology, University of Birmingham, told Science Media Centre, “This study is impressive in its scale. However, the associations observed are very small correlative. It is dangerous to suggest, even unintentionally, to women that changing their sleep patterns will significantly alter their risk of breast cancer.”

According to the Canadian Cancer Society, breast cancer is the most common cancer among Canadian women (excluding non-melanoma skin cancers), being the second-leading cause of death from cancer.

In 2017, an estimated 26,300 women were diagnosed with breast cancer — 25% of all new cancer cases in women, according to the Society. 5,000 women died from breast cancer which represented 13% of all cancer deaths in women in 2017.