Working night shifts for more than 30 years could double women's risk of developing breast cancer, research suggests.

Nurses, cleaners, care workers, some shop workers, call centre handlers and others who work night shifts for a long term can have a twice as high risk of developing the disease than those who don't, the new study found.

Canadian researchers examined 1,134 women with breast cancer and 1,179 women without the disease, but of the same age.

Women were questioned about their work and shift patterns and researchers also assessed the hospital records for the women who suffered from the disease.

About a third of the women had a history of night shift work.

The study, published in Occupational and Environmental Medicine, found that those who had worked nights for 30 or more years were twice as likely to have developed the disease, after taking account of potentially influential factors, although the numbers in this group were comparatively small.


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No such relationship was found if women worked for less than 30 years doing shift work.

Previous research has linked the disease with shift work done by nurses but the latest study found that the associations were similar among those who worked in healthcare and those who did not.

"An association between more than 30 years of night shift work in diverse occupations and breast cancer is supported here, consistent with other studies among nurses," the authors said.

"As shift work is necessary for many occupations, understanding of which specific shift patterns increase breast cancer risk, and how night shift work influences the pathway to breast cancer is needed for the development of healthy workplace policy."

But experts cautioned that the increased cancer risk is yet to be confirmed.

Dr Jane Green, clinical epidemiologist at the University of Oxford, said: "This seems to be a well-conducted study with the benefit of more detailed occupational history than in many studies.

"The finding of an increased risk of breast cancer in women with a long history of shift work adds to similar results from some previous studies, but does not change the existing consensus: that while there is some evidence to associate increased risk of breast cancer with very long term shift work, the evidence is not yet sufficient to be sure and certainly not sufficient to give a public health message about working shifts.

"With further work, the increased cancer risk may not be confirmed; and even if it is, could turn out to be explained by differences in known breast cancer risk factors among shift workers vs non-shift workers. In other words, it might not be the shift work itself that is to blame. We therefore cannot interpret this study to say shift work causes cancer."

Dr Hannah Bridges, senior information officer at the charity Breakthrough Breast Cancer, added: "This is one of a few studies that suggest working night shifts for many years may increase breast cancer risk. However, we don't yet know that shift work is a risk factor for breast cancer, so we'd urge women not to panic.

"We need to better understand why night work might increase breast cancer risk. Shift work may lead to unhealthy lifestyle habits that could independently increase the risk of breast cancer, so we'd encourage all women to take part in regular physical activity, maintain a healthy weight and reduce their alcohol intake."

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  • Kathy Bates

    The actress, who beat ovarian cancer close to a decade ago, shared last month that she had been <a href="http://www.huffingtonpost.com/2012/09/12/kathy-bates-breast-cancer-double-mastectomy_n_1878208.html">diagnosed with breast cancer and underwent a double mastectomy</a>, The Huffington Post reported at the time. "Luckily, I don't have to undergo radiation or chemo," <a href="http://www.people.com/people/article/0,,20628972,00.html">she told <em>People</em> magazine</a>. "My family calls me Kat because I always land on my feet and thankfully this is no exception." <a href="http://www.huffingtonpost.com/2012/09/12/kathy-bates-breast-cancer-double-mastectomy_n_1878208.html">She also shared the news on Twitter</a> -- with her signature sense of humor intact. "I don't miss my breasts as much as I miss Harry's Law. ;-) Thanks for all the sweet tweets," she wrote. "Y’all kept me going."

  • Maura Tierney

    Tierney was diagnosed with breast cancer in 2009, but she didn't open up publicly about it until earlier this year. "I remember thinking, 'I'm so young, this can't be happening,'" <a href="http://www.people.com/people/article/0,,20611140,00.html">she told <em>People</em> magazine</a>. "In 2009, I was diagnosed with breast cancer and found out I would need chemotherapy," <a href="http://www.chemomythsorfacts.com/index.html">she said in a video for the Chemotherapy Myths Or Facts campaign</a>. "I asked myself all these questions and was utterly terrified, not just because of the cancer diagnosis, but the fear of chemo itself." And that sense of the unknown is what triggered Tierney, whose cancer was found in its early stages, to sign up as a spokesperson for the campaign. "It's important that you feel educated and confident during this time," <a href="http://www.chemomythsorfacts.com/index.html">she said in her introductory video</a>.

  • Judy Blume

    The beloved author of favorites such as "Are You There God? It's Me, Margaret," and "Tales Of A Fourth Grade Nothing," revealed that she was diagnosed with invasive ductal carcinoma in a <a href="http://www.judyblume.com/blog.php">blog post on her website this past September</a>. "I haven’t eaten red meat in more than 30 years. I’ve never smoked, I exercise every day, forget alcohol -- it’s bad for my reflux -- I’ve been the same weight my whole adult life," <a href="http://www.judyblume.com/blog.php">she wrote</a>. "How is this possible? Well, guess what -- it’s possible." <a href="http://www.huffingtonpost.com/2012/09/05/invasive-ductal-carcinoma-judy-blume-breast-cancer_n_1858418.html">Blume had a mastectomy</a> on July 30. <a href="http://www.judyblume.com/blog.php">She wrote in her blog</a>: <blockquote>As I've told my friends who've also been treated for breast cancer, I've joined The Club -- not one I wanted to join or even thought I would ever be joining -- but here I am. I’m part of this Sisterhood of the Traveling Breast Cells (apologies to Ann Brashares). Medical diagnoses can leave you feeling alone and scared. When it comes to breast cancer you’re not alone, and scary though it is, there’s a network of amazing women to help you through it.</blockquote>

  • Ann Romney

    Wife to Republican presidential hopeful Mitt Romney, Ann was <a href="http://www.huffingtonpost.com/2012/05/03/ann-romney-breast-cancer_n_1475950.html">diagnosed with breast cancer in early 2009</a>. "It's great to have loved ones around you," <a href="http://www.americasradionewsnetwork.com/ann-romney-reflects-on-her-personal-battle-with-breast-cancer">she told America's Radio News Network in an interview</a> earlier this year of where she found post-diagnosis comfort. "And you just fight these battles, listen you don't fight them alone. You fight them with friends and with family. And you put your arms around each other and you move forward." Romney, whose mother and grandmother died from ovarian cancer and whose great-grandmother died from breast cancer, told the program <a href="http://www.americasradionewsnetwork.com/uploads/mp3/showclips/05-03-12ANNROMNEY1.mp3">she's most grateful to have been diagnosed early</a> -- she needed surgery and radiation, but not chemo. "Life is an interesting game, and you just always deal with whatever you're dealt with that day or that week or that month or that year," said Romney, who has <a href="http://www.huffingtonpost.com/2012/06/18/multiple-sclerosis-celebrities_n_1606174.html">also been diagnosed with multiple sclerosis</a>. "No matter what you're living through, we all push forward."

  • Edie Falco

    The TV star was diagnosed with breast cancer in 2003, when she was starring in "The Sopranos." "I take very good care of myself (mostly because I didn’t many years ago), and that served me well during chemo," <a href="http://www.health.com/health/article/0,,20411264,00.html">she later wrote in an article for <em>Health</em> magazine</a>. "Running every day made me feel calm and strong, even as my self-image suffered from my hair falling out." After her cancer went into remission, Falco decided to adopt -- her baby boy, Anderson, was born in January 2005. She later <a href="http://www.redbookmag.com/fun-contests/celebrity/edie-falco-nurse-jackie">adopted a daughter</a>, as well. "Obviously, it wasn’t meant for me to die of cancer at 40," <a href="http://www.health.com/health/article/0,,20411264_2,00.html">she wrote</a> in <em>Health</em>. "Every day my life surprises me, just like my cancer diagnosis surprised me."

  • Angelina Jolie

    Angelina Jolie had to have a preventative double mastectomy. Writing for the New York Times, the star revealed that she decided to have the procedure when she found that she was carrying the BRCA1 gene which "sharply increases" the risk of contracting cancer. Doctors told Angelina that she had an 87% risk of breast cancer and a 50% risk of ovarian cancer, and she made the brave decision to have a double mastectomy.

  • Suzanne Somers

    The "Three's Company" and "Step By Step" actress was first diagnosed with breast cancer in 2000. "We were silent, hardly talking, in disbelief, like this can't be happening, wondering is this a little blip or the end of my life?" <a href="http://www.people.com/people/archive/article/0,,20134247,00.html">she told <em>People</em> magazine in 2001</a>, of hearing the news for the first time with her husband Alan Hamel. Just earlier this year -- more than a decade since her diagnosis -- Somers shared with <em>People</em> that she <a href="http://www.people.com/people/article/0,,20567432,00.html">underwent an experimental breast reconstruction surgery</a>, to repair the damage from a lumpectomy and radiation treatments.

  • Olivia Newton-John

    The "Grease" star and singer was diagnosed with breast cancer in 1992 after feeling a lump in a self exam -- <a href="http://ww5.komen.org/BreastCancer/OliviaNewtonJohn.html">her treatment included</a> surgery, chemotherapy, a radical mastectomy and reconstruction. "When you're first diagnosed, people are pulling you in every direction: Do this! Do that! You really have to gather yourself, because you're the one who has to make the hard choices," <a href="http://ww5.komen.org/BreastCancer/OliviaNewtonJohn.html">she said in a Q&A on Susan G. Komen For The Cure's website</a>. "I researched a lot and felt satisfied with my course of treatment. It was sort of an East-meets-West approach." And that meant taking care of her <em>whole</em> body, not just the cancer. "I did everything I could to take care of myself -- body, mind, and spirit," <a href="http://www.everydayhealth.com/breast-cancer/mylife/olivia-newton-john/questions.aspx">she told EverydayHealth.com</a>. "I look at my cancer journey as a gift: It made me slow down and realize the important things in life and taught me to not sweat the small stuff."

  • Giuliana Rancic

    The 36-year-old "E! News" host announced last October on<a href="http://theclicker.today.msnbc.msn.com/_news/2011/10/17/8363134-es-giuliana-rancic-reveals-she-has-breast-cancer" target="_hplink"> NBC's Today show</a> that she has breast cancer, and that she was alerted to the cancer via a mammogram during her third in vitro fertilization attempt. "Through my attempt to get pregnant for the third time, we sadly found out that I have early stages of breast cancer," she said <a href="http://theclicker.today.msnbc.msn.com/_news/2011/10/17/8363134-es-giuliana-rancic-reveals-she-has-breast-cancer" target="_hplink">on the Today show</a>. "It's been a shock. A lot of people have been asking, we saw that you went and got IVF, are you pregnant? But sadly, we've had to put that off." Rancic underwent a double lumpectomy and removal of several of her lymph nodes, but she later went on the TODAY show last December to say that the cancer was not completely cleared by those treatments and that she will <a href="http://www.huffingtonpost.com/2011/12/05/double-mastectomy-giuliana-rancic-breast-cancer_n_1129433.html" target="_hplink">undergo a double mastectomy</a>. This year, Rancic finally got her happy ending, <a href="http://www.huffingtonpost.com/2012/09/12/edward-duke-rancic-photo-giuliana-bill-rancic-baby-boy_n_1876694.html">with the birth of son Edward Duke</a> via gestational surrogate on August 29.

  • Wanda Sykes

    In a 2011 interview with Ellen DeGeneres, Wanda Sykes revealed that she had been <a href="http://www.huffingtonpost.com/2011/09/23/wanda-sykes-breast-cancer_n_977761.html#s312402&title=Wanda_Sykes" target="_hplink">diagnosed with breast cancer</a> and underwent a double mastectomy. "I had breast cancer. Yeah, I know it's scary," Sykes said in the interview. "This was in February. I went for the reduction. I had real big boobs and I just got tired of knocking over stuff. Every time I eat ... Oh lord. I'd carry a Tide stick everywhere I go. My back was sore so it was time to have a reduction." After the reduction, the pathology report found ductal carcinoma in situ in her left breast, which prompted Skykes, who has a <a href="http://www.people.com/people/article/0,,20531010,00.html" target="_hplink">family history of breast cancer</a>, to opt for a double mastectomy. And while the diagnosis is scary, she hasn't lost her <a href="http://www.huffingtonpost.com/2011/09/23/wanda-sykes-breast-cancer_n_977761.html#s312402&title=Wanda_Sykes" target="_hplink">signature humor</a>. "I was like, 'I don't know, should I talk about it or what?' How many things could I have? I'm black, then lesbian. I can't be the poster child for everything ... At least with the LGBT issues we get a parade, we get a float, it's a party. [But] I was real hesitant about doing this, because I hate walking. I got a lot of [cancer] walks coming up."

  • Christina Applegate

    In 2008, actress Christina Applegate shared in a "Good Morning America" interview that she had been <a href="http://abcnews.go.com/GMA/story?id=5606034&page=1" target="_hplink">diagnosed with breast cancer</a> at the age of 36 -- she opted for a bilateral mastectomy instead of radiation or chemotherapy. "I didn't want to go back to the doctors every four months for testing and squishing and everything. I just wanted to kind of get rid of this whole thing for me. This was the choice that I made and it was a tough one," she said <a href="http://abcnews.go.com/GMA/story?id=5606034&page=1" target="_hplink">in the interview</a>. "Sometimes, you know, I cry. And sometimes I scream. And I get really angry. And I get really upset, you know, into wallowing in self-pity sometimes. And I think that it's all part of the healing." Perhaps the best healing of all came in 2011 when Applegate gave birth to baby Sadie with musician Martyn LeNoble. "She's healed me in so many ways. She's just made my life so much better. I've been kind of sad for a long time, and she's just opened my whole soul," Applegate <a href="http://www.people.com/people/archive/article/0,,20467525,00.html" target="_hplink">told <em>People</em></a> in an exclusive interview in 2011.

  • Melissa Etheridge

    In 2005, rock-and-roll artist Etheridge underwent a lumpectomy and five rounds of chemotherapy and radiation to eradicate her breast cancer. "I had been running along in my life at a fast pace. When I heard it was cancer, I just stood still," Etheridge told <em>Shape</em> magazine in a 2009 interview. "My life passed over me like a big wave, and after, I was left there standing. This turned out to be a very good thing. I stopped. I looked at my life, I looked at my body and spirit." In the midst of her treatment, Etheridge found out she was <a href="http://www.msnbc.msn.com/id/6994469/ns/dateline_nbc/t/melissa-etheridges-brave-comeback/" target="_hplink">nominated for a Grammy</a> for her song "Breathe" -- and while she wasn't sure she'd make an appearance at first, Etheridge ultimately decided not only to attend, but to perform in a Janis Joplin tribute. Taking to the stage bald and with no eyebrows -- a side-effect of the chemo -- she belted out Joplin's classic, "Piece Of My Heart." "It was very special that I had been presented with a day, that I could come back into this entertainment world, and show everyone that you are back and okay, and thought, okay," Etheridge told <a href="http://www.msnbc.msn.com/id/6994469/ns/dateline_nbc/t/melissa-etheridges-brave-comeback/" target="_hplink">MSNBC at the time</a>. "I'm going to do this. And I'm not gonna be afraid of the truth. The truth is, yes I had cancer. Yes, I got it out of me. Yes, I went through chemotherapy. Yes, I'm bald." Check out Etheridge's breast cancer causes on her <a href="http://www.melissaetheridge.com/pinkpage" target="_hplink">Pink Rage website</a>.

  • Robin Roberts

    ABC's "Good Morning America" co-host Robin Roberts was diagnosed with breast cancer in 2007. "I never thought I'd be writing this. ... <a href="http://abcnews.go.com/GMA/CancerPreventionAndTreatment/abcs-robin-roberts-breast-cancer/story?id=3430554" target="_hplink">I have breast cancer</a>," she said in a message released by ABC in August 2007. While working on a tribute to her colleague Joel Siegel, who had died from cancer, Robins reported on how key early detection is -- and, taking her own advice, she did a self breast exam and found a lump. "Much as I was hoping the doctor would say it was nothing, she did a biopsy and confirmed that the lump I'd found was indeed an early form of breast cancer," Robins <a href="http://abcnews.go.com/GMA/CancerPreventionAndTreatment/abcs-robin-roberts-breast-cancer/story?id=3430554" target="_hplink">continued in her statement</a>. Robins underwent a partial mastectomy, chemotherapy and radiation. In 2008, she told <em>People</em> magazine that she <a href="http://www.people.com/people/archive/article/0,,20238177,00.html" target="_hplink">complemented her regular doctor's visits</a> with acupuncture, exercise and advice from a nutritionist. "Yes, I am living with cancer," she <a href="http://www.people.com/people/archive/article/0,,20238177,00.html" target="_hplink">told <em>People</em></a>. "But don't go 'woe is me.' I don't want it. Don't need it. I'm still in the game. I don't want to say 'survivor.' I want to thrive." Earlier this year, Roberts announced that she was diagnosed with a <a href="http://www.huffingtonpost.com/2012/09/20/bone-marrow-transplant-robin-roberts-myelodysplastic-syndrome_n_1900324.html">rare blood disorder called myelodysplastic syndrome</a>.

  • Kylie Minogue

    Australian singer Minogue was first diagnosed with breast cancer in May 2005 and underwent surgery and chemotherapy treatment. "When you are stripped of everything and you have to grow your eyelashes back, grow your hair back, it's just astonishing," Minogue told British <em>Glamour</em> magazine. "It's hard to express what I've learned from that, but a deep psychological and emotional shift has obviously taken place." This open and honest approach to her diagnosis led Minogue to be voted the <a href="http://www.reuters.com/article/2010/09/03/us-cancer-celebrities-idUSTRE6820P120100903" target="_hplink">most inspirational breast cancer celebrity</a> in an online British-based poll, Reuters reports.

  • Sheryl Crow

    Singer Sheryl Crow was <a href="http://articles.cnn.com/2006-10-06/health/crow.cancer_1_breast-cancer-early-detection-cancer-patients?_s=PM:HEALTH" target="_hplink">diagnosed with breast cancer</a> in 2006 and, thanks to early detection, underwent a minimally invasive surgery and seven weeks of radiation therapy. Crow told <em>Health</em> magazine that <a href="http://www.health.com/health/article/0,,20411904_2,00.html" target="_hplink">she saw a nutritionist</a> when she was first diagnosed and began a diet full of fish, walnuts, colorful vegetables, fiber and healthy spices. "I kept my breast cancer tattoos -- where the radiation was lined up on my chest," Crow told <em>Health</em>. "Once in a while I look at it to remind myself that I have to put on my oxygen mask first before I put it on anybody else." Today, Crow is focused on spreading the message of early detection. In 2010, she <a href="http://content.usatoday.com/communities/entertainment/post/2010/08/sheryl-crow-opsns-breast-cancer-imaging-center-/1" target="_hplink">founded the Sheryl Crow Center</a> as part of the Pink Lotus Breast Center, which was founded by her own surgeon, ABC News reports. This past June, Crow also revealed that she was diagnosed late last year with a <a href="http://www.huffingtonpost.com/2012/06/05/benign-brain-tumor-sheryl-crow_n_1572008.html">benign brain tumor</a>.

  • Cynthia Nixon

    In 2008, the "Sex and the City" star went public with her <a href="http://www.huffingtonpost.com/2008/04/15/cynthia-nixon-on-her-love_n_96749.html" target="_hplink">cancer diagnosis</a>, revealing that she found a lump in its early stages and had it removed through radiation, The Huffington Post reported at the time. Nixon wrote in a 2008 <em>Newsweek</em> article that her mother was <a href="http://www.thedailybeast.com/newsweek/2008/10/03/a-family-of-strong-women.html" target="_hplink">diagnosed with breast cancer twice</a> -- the first time, Nixon was just 13. "I feel like I have a very <a href="http://www.huffingtonpost.com/2011/10/03/slideshow_n_991609.html#s384104&title=Cynthia_Nixon" target="_hplink">concrete story to tell</a>. My story isn't just my story, it's mine and my mother's story," the <a href="http://ww5.komen.org/" target="_hplink">Susan G. Komen for the Cure</a> spokesperson has said.