Benjamin Franklin once said, “Early to bed and early to rise makes a man healthy, wealthy and wise.” For women, one of the benefits of being an early riser may be a reduced risk of developing breast cancer.
This is according to research first presented in November 2018 at the NCRI Cancer Conference in the United Kingdom and recently published in the British Medical Journal, reports CNN. But why are some people early birds while others are night owls? Experts say hundreds of genes influence our circadian rhythms, which regulate when we sleep and wake, among other biological functions.
An investigation of more than 180,000 enrolled with the UK Biobank study—a national and international health resource—and over 220,000 women who were a part of the Breast Cancer Association Consortium (BCAC) study examined whether sleep traits were a risk factor for breast cancer. Participants preference for waking up early or late was also a part of the data collected.
From the BCAC analysis, those with a preference for mornings saw a reduced risk of breast cancer by 40% compared to those who preferred evenings. Women who slept more than seven to eight hours also had a 20% increased risk of breast cancer per additional hour slept.
UK Biobank data revealed that morning preference was associated with a 48% lower risk of breast cancer. Translated into absolute numbers rather than percentages, that means that 10 out of 1,000 women who reported being morning people developed breast cancer, compared to 20 out of 1,000 women who said they were evening people.
“Sleep is likely to be an important risk factor for breast cancer, but it isn’t as large as other well-established risk factors like [body mass index] or alcohol,” said Rebecca Richmond, lead author and a research fellow at the MRC Integrative Epidemiology Unit at the University of Bristol, in 2018.
Luca Magnani, PhD, senior research fellow in the department of Surgery & Cancer at Imperial College London, told the Science Media Centre, “It is important to note that these data do not suggest in any way that modifying sleep habits could eventually lead to a decrease in risk of breast cancer.” Instead, Magnani says, the research suggests there is an association between breast cancer risk and an unmodifiable genetic trait linked to morning or night preference.
Even if you can’t change your genetic predisposition from being a night owl to a morning lark, however, it’s clear that getting the right amount of quality sleep is important to health. For more on how sleep affects cancer risk, check out this blog post from Michael Breus, PhD.