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TX: 16.03.09 - Breast Cancer and Nightshifts

PRESENTER: JULIAN WORRICKER
Downloaded from www.bbc.co.uk/radio4
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WORRICKER
Now you may have heard a 成人快手 Scotland report this morning that the Danish government is paying compensation to some women with breast cancer. The theory is that they contracted the disease after working years of nightshifts. So what's the evidence and what might be the impact, if any, on long term nightshift workers here? Well Carolyn Atkinson has more, Carolyn.

ATKINSON
Well all of this came about because of a decision by the International Agency for Research on Cancer, they're called IARC, and they're part of the World Health Organisation. Now IARC categorises cancer risks of all sorts of things and following research published in the Lancet in 2007 it decided that nightshifts are a probable cause of breast cancer, so they're included in a category called 2A which is a list of probable causes of cancer along with all sorts of other probable causes like solvents. Now in Denmark they have something called a workers' compensation fund and people can claim for compensation for occupational diseases as well as accidents if they're listed under this category 2A. So over the past year or so 38 women have had payouts of between £6,000 and £125,000. Now in total 70 people applied and some of them of course failed and those that failed did so because, for example, they'd only done limited nightshifts or perhaps, for example, they had a family history of breast cancer.

So the key question is: how do nightshifts increase your risk of breast cancer? Well some of the research that helped persuade IARC was done by Johnni Hansen. He's from the Danish Cancer Society and he says it's all to do with the hormone melatonin.

HANSEN
Our theory is that when you work during the night and come later to bed you're exposed to lights in the eyes and when you're exposed to lights you produce less of the hormone called melatonin. And it seems like that this hormone protects you against specific breast cancer.

ATKINSON
And so the theory goes if you don't get enough sleep in the dark you could increase your risk?

HANSEN
Yeah, but it's not directly related to the sleep, it's related to the exposure to light.

ATKINSON
And interestingly Johnni Hansen says it actually takes a week for the body to readjust itself, so just by sleeping the next day, after a nightshift, for example, that won't actually get you back to square one.

WORRICKER
Well let's have a word with Dr Kat Arney from Cancer Research UK. Good afternoon.

ARNEY
Hello.

WORRICKER
This research talks about a probable cause, as Carolyn was outlining, how sure are we that nightshifts increase one's risk of breast cancer?

ARNEY
Well it's a breast cancer risk, there is some evidence and we can't say absolutely 100% yes because a lot of the studies that have been done, there's a lot of things that we call confounding factors. So, for example, many of the studies that have found an increase in risk haven't corrected the things like lifestyle factors - alcohol consumption, patterns of childbirth - having children later in life - those kinds of things. So a couple of studies have shown a correlation between working nightshifts, particularly over a long time, we're not talking doing a few shifts, we're talking over 10, 20, 30 years of consistent nightshifts. The evidence, as IARC has said, is probable that it increases the risk of cancer in humans but it's not absolutely 100% sure. And we don't know, say, compared to other lifestyle factors what percentage increase in risk this might be.

WORRICKER
No but you would still presumably point to other lifestyle factors that we are very familiar with and say they are massively more significant and there are studies to back that up.

ARNEY
There's certainly more studies for other lifestyle factors like the role of hormones, the role of alcohol and obesity and things like that. What we really need to see is a better study on shift patterns and breast cancer and that's something that I think the Health and Safety Executive is working on at the moment.

WORRICKER
And presumably not just breast cancer, I mean I'm reading an e-mail here from Luke, who got in touch at the start of the programme when he heard what we were going to talk about, and he says: I spent several decades doing nightshifts for six winter months of every year and I just wonder whether that might have contributed to my rather troubled later health, including leukaemia, he says, has there been any research into any male problems in this area?

ARNEY
And there have been studies looking at other types of cancer. I mean in the male case, particularly things like prostate cancer, and they haven't really found any kind of strong link, they certainly haven't been conclusive. And the reason that it's focused on breast cancer is because that's where the evidence is the strongest. Cancer is a common disease, overall it affects one in three people in the UK, so it's very difficult to pin it down and say it must be due to nightshifts, it could be due to many things - could be due to lifestyle factors or it could just be down to bad luck or your genes as well.

WORRICKER
And just picking up on something else that Johnni Hansen said. What's the evidence with regards to the influence that our exposure to light and dark has on our propensity to have cancer?

ARNEY
There's a sort of a chain that we can follow here in that we know that - so there's some evidence that working nightshifts increases your risk of breast cancer, we know from things like lab studies that melatonin is very important and is probably linked to cancer. What we don't have is that definitive link that says if you work nightshifts you mess up your melatonin and it is causing cancer in this way. There's sort of a missing link there that we don't really have and we're only going to be answer that with some more research into it. So it's certainly something that we do need to investigate, it's something that the Health and Safety Executive is taking seriously and it's something that Cancer Research UK is very interested in, in seeing what people have to say about it and looking at future research, definitely.

WORRICKER
Because our modern lifestyles - I mean they determine that we are exposed to far more light than we used to be by definition aren't we.

ARNEY
Absolutely, just recreational light at night - watching the telly, turning the lights on, going out late, street lights - all these kind of things are exposing us to light that in evolutionary terms we're not used to expect at that kind of time of day or night rather. So yeah it's certainly - it may be impacting on our risk of cancer but it's really not clear how and how much.

WORRICKER
Carolyn is still here, what news for British workers worried about possibly problems here Carolyn?

ATKINSON
Well as Dr Arney said the Health and Safety Executive have been looking at this issue. Way back in 2002 they started looking at it and they've commissioned research which is expected to report back by about 2011. But so far they consider fatigue to be the biggest risk of doing shift work and they don't say that any immediate changes are needed. In Holland one of their trade unions there is reported to be asking their members who contracted breast cancer and who've done at least 10 years of nightshifts to contact them because they're trying to bring a legal case there.

WORRICKER
Carolyn thank you and thanks as well to Dr Kat Arney from Cancer Research UK.

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