|
 While previous studies have linked inconsistent sleep schedules and
getting too much rest to an increased risk of breast cancer,
researchers haven't looked as often at how much women's wake-up time
might impact this risk, researchers note in the BMJ.
For the current analysis, researchers analyzed genetic variants
associated with three sleep traits: sleep duration, insomnia, and a
so-called morning or evening chronotype, referring to early or late
risers. They looked at data on 180,216 women in the UK Biobank study
and 228,951 women in the Breast Cancer Association Consortium (BCAC)
study.
In the UK Biobank study, among every 100 women who were early
risers, there was one fewer case of breast cancer than among every
100 women who were late risers. But there wasn't a clear connection
between breast cancer and sleep duration or insomnia.
In the BCAC group, women who woke up early also had a lower risk of
breast cancer. In this study, sleeping more than the recommended 7
to 8 hours a night was associated an increased risk - 19% for every
extra hour.
"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 in the development of
breast cancer," said Rebecca Richmond, lead study author and a
researcher at the University of Bristol in the U.K.
"One particular mechanism which might explain the link, known as the
`light-at-night' hypothesis, involves the suppression of melatonin
levels in women exposed to artificial night at light, which in turn
influences various hormonal pathways which might increase risk of
breast cancer," Richmond said by email.
But women shouldn't rush to reset their alarm clocks to lower their
breast cancer risk, Richmond said.
"Our main findings were based on women's reported morning or evening
preference, rather than actually whether they get up earlier or
later in the day," Richmond noted.
[to top of second column] |
Another drawback is that participants were all of European ancestry,
and results might differ for women from other racial and ethnic
groups.
Most women who get breast cancer develop these tumors after age 50,
and they may be more prone to these tumors with a family history,
certain genetic mutations, dense breast tissue, early puberty or
late menopause, according to the U.S. Centers for Disease Control
and Prevention.
While women can't control any of those risk factors, there are other
risk factors related to lifestyle that can be altered, according to
the CDC. These include being physically inactive, overweight,
drinking alcohol, having a first pregnancy after age 30, not
breastfeeding, and taking some forms of hormonal birth control pills
and hormone replacement therapy for menopause symptoms.
Sleep might also increase the risk, along with smoking, exposure to
certain chemicals, and hormone changes caused by night shift work,
according to the CDC.
The current analysis wasn't a controlled experiment designed to
prove that specific sleep habits might directly cause breast cancer.
It's also not clear from the study whether women's preferred early
or late wake-up time (conformed) with their work hours, said Dr. Eva
Schernhammer, author of an accompanying editorial and a researcher
at the Medical University of Vienna and Harvard Medical School in
Boston. Being an early riser might make women's wake up time better
match a typical 9 to 5 workday that is common for many jobs.
"The majority of women are neither morning or evening types, but
somewhere in between on that spectrum, hence, any potential risks
are likely to affect a relatively small proportion of women,"
Schernhammer said by email. "However, sleep and work timing might be
more important than previously thought."
SOURCE: http://bit.ly/2Y4PIEI BMJ, online June 26, 2019.
[© 2019 Thomson Reuters. All rights
reserved.] Copyright 2019 Reuters. All rights reserved. This material may not be published,
broadcast, rewritten or redistributed.
Thompson Reuters is solely responsible for this content. |
