In a new study, researchers found that being a morning person (popularly known as larks) is associated with a lower risk of developing breast cancer than being an evening person (popularly known as owls).
They also found that sleeping longer than the recommended 7-8 hours a night may increase breast cancer risk.
The research was conducted by an international research team.
One in seven women will develop breast cancer at some stage in their lives.
Previous studies have shown a link between night shift work and risk of breast cancer.
It has shown that disrupted sleep patterns, light exposure at night, and other lifestyle factors may contribute to cancer development.
However, there has been much less research into the potential effects of sleep habits on breast cancer risk.
In the new study, the team analyzed genetic variants linked to three particular sleep traits, including morning or evening preference, sleep duration, and insomnia, in 180,216 women in the UK Biobank study and 228,951 women in the Breast Cancer Association Consortium (BCAC) study.
The researchers found that being a ‘morning person’ was linked to a slightly lower risk of breast cancer than being an ‘evening person’.
There was little evidence for a link with sleep duration and insomnia symptoms.
The finding provided some supportive evidence for a protective effect of morning preference on breast cancer risk and showed a potentially harmful effect of longer sleep duration (more than the recommended 7-8 hours) on breast cancer.
The researchers suggest that people need to have good sleep habits to reduce their cancer risk.
Further work needs to uncover possible reasons for the associations between sleep disruption and breast cancer
The study is published in The BMJ.
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