The study on several women found some evidence for a causal link between sleeping for longer and breast cancer.
Washington DC: Turns out, early to bed and early to rise can also lower your risk of developing breast cancer.
The research was presented at the 2018 NCRI Cancer Conference.
The study on several women, which was investigating whether the way people sleep can contribute to the development of breast cancer, also found some evidence for a causal link between sleeping for longer and breast cancer.
Researchers at the University of Bristol found that a preference for mornings reduced the risk of breast cancer by 40 to 48 percent compared with being an evening type (an 'owl'). It also found that women who slept longer than the recommended seven to eight hours had a 20 percent increased risk of the disease per additional hour slept.
Dr Rebecca Richmond of the University of Bristol, UK said, "We would like to do further work to investigate the mechanisms underpinning these results, as the estimates obtained are based on questions related to morning or evening preference rather than actually whether people get up earlier or later in the day. In other words, it may not be the case that changing your habits changes your risk of breast cancer; it may be more complex than that."
"However, 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," she said.
"We also found some evidence for a causal effect of increased sleep duration and sleep fragmentation on breast cancer, assessed using objective measurements of sleep obtained from movement monitors worn by participants," she added.
The researchers believe their findings have implications for policy-makers and employers. Dr Richmond said: "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."
Cliona Clare Kirwan, from the University of Manchester, who was not involved in this research, said: "These are interesting findings that provide further evidence of how our body clock and our natural sleep preference is implicated in the onset of breast cancer."
"We know already that night shift work is associated with worse mental and physical health. This study provides further evidence to suggest disrupted sleep patterns may have a role in cancer development," she said.