Being a morning person could affect cancer risk
Are you able to bounce out of bed in the morning and greet the sunrise, or is it an uphill struggle to force yourself into the land of the living each day? It turns out that whether you’re a morning-loving “lark”, or a darkness-craving night owl can have far reaching effects. By studying data from 500,000 individuals, researchers at the University of Bristol have found that women who are “morning people” have a much lower risk of breast cancer than those who aren’t. But why? Adam Murphy spoke to Rebecca Richmond who presented the work at National Cancer Research Institute’s Cancer Conference in Glasgow.
Rebecca - So of interest to our particular study was looking at sleep characteristics in relation to breast cancer risk, and we looked at three specific sleep traits of interest. So one of those was an individual's preference to be a morning or an evening person. A second one was we asked individuals about how many hours of sleep they were getting each night. And finally a question also asked about insomnia risk - so that's difficulty getting to sleep or waking up in the night. In these two large studies we looked at these questions and we also looked at genetic variants which were associated with these various sleep traits and looked at the contribution of these towards risk of breast cancer. What we found was individuals reporting to have a preference towards the morning were actually protected against risk of breast cancer.
Adam - How much were they protected by?
Rebecca - In terms of looking at the extremes, so definite morning people versus definite evening people, there we actually showed a 40 percent reduction in risk of breast cancer.
Adam - That's a fairly massive reduction for something as taken for granted as sleep.
Rebecca - Yes so it's quite interesting findings. I suppose we have to also put this in some context in terms of actually looking at absolute risk - so these 40 percent estimates are relative estimates. In terms of a bigger perspective, we know that one in seven women will develop breast cancer at some stage during their lives. So it's very important to recognize that although sleep may be one potential modifiable risk factor actually there are some other very important risk factors which we know about. So it's very important to, for example, maintain a healthy weight, to not smoke, and to drink in moderation. And so at this stage it is quite early findings with regards to the actual impact of sleep on breast cancer. But this is where it goes some way towards putting sleep on the research agenda for breast cancer.
Adam - Do we have any idea why a preference for sleep time is a factor in this?
Rebecca - So it is quite complicated to think about what it actually is about being a morning person that protects these women. In terms of potential mechanisms, one quite well known hypothesis is regarding the effects of light at night which might be a potential indicator as to why those individuals who reported to be evening people were more at risk. So, the idea behind this light at night hypothesis is that individuals who stay awake later into the evening have more exposure to artificial light and that this can cause disruption in hormone levels which might put these women at risk. Some other potential links between morning and evening preference in breast cancer relate to potential differences in metabolism and also differences in other lifestyle behaviours.
Adam - Does that imply then that shifting your behaviour, shifting when you sleep, would help or is it a genetic thing that we can’t really affect?
Rebecca - We did look at this and the genetic component making up morning or evening preferences is relatively small, so around 10 percent. So that indicates that this behaviour is modifiable. But at this stage we think it's too early to really say that we should advocate that women, for example, get up earlier. And we need to try to make this distinction between what it is about morning preference compared with actual behaviour. Because there is some argument to say that individuals who have a tendency towards an evening preference, by disrupting that, by making them get up early, actually that could lead also to increased risk because there’s a sort of misalignment between their biological clock and their kind of social clock as it were.
Adam - What is next for you in your group? What's the next plan?
Rebecca - So there is evidence to suggest our body clock is also potentially important for other conditions and other diseases, and other types of cancer have also been suggested to be potentially impacted by these various sleep related exposures. So we're going to also, hopefully, look at other types of cancer. And also other types of diseases using the same type of methods that we've been applying in this study and look at those particularly at risk of disease.