In an observational study of 180,215 participants of the UK Biobank project, the team of researchers at the University of Bristol, Massachusetts General Hospital, Boston, the University of Exeter and the University of Manchester, looked at whether women preferred to sleep in the morning or evening, and examined whether this preference was associated with the development of breast cancer.

The team found that those with ‘lark’ tendencies, who preferred to be awake in the morning, appeared to have a lower risk of developing breast cancer, compared to ‘night owls’. 

The second part of the study looked at genetic variants called SNPs. The team found that genetic variants that are known to be associated with morning preference, were also associated with a reduced risk of developing breast cancer. These findings were repeated with another group of 228,951 participants of the Breast Cancer Association Consortium.

The team also found some links between sleeping for longer and breast cancer risk – with further studies needed to validate the findings.

Dr Richard Berks, Senior Research Communications Officer at Breast Cancer Now, said:

These intriguing results add to the growing body of evidence that there is some overlap between the genetics of when we’d prefer to sleep and our breast cancer risk, but more research is required to unravel the specifics of this relationship.

Preferring to sleep all morning, and being able to, are two different things – and we now need to understand how women’s actual sleeping habits may affect their breast cancer risk. While these are interesting findings that warrant further investigation, it is currently too early to make any recommendations to women about their sleeping patterns.

What we can be certain of is that all women – larks and owls – can reduce their risk of breast cancer by exercising regularly, maintaining a healthy weight and reducing their alcohol intake.