March 23, 2009 — Denmark has become the first country to pay government compensation to women who developed breast cancer after long spells of working at night.
The ruling, reported last week by many media outlets as news, was actually made last year.
The Danish National Board of Industrial Injuries explains on its Web site that in 2008, breast cancer after night-shift work was recognized as an industrial injury in 38 of 75 cases that were submitted to the Occupational Disease Committee. Compensation was granted in all but 1 of the 38 cases, and was paid by the employer's industrial-injuries insurance.
The cases that won compensation involved women who typically worked at least 1 night a week for at least 20 to 30 years, and where there were "no other significant factors that might explain the development of breast cancer," the Board said.
Some of the cases were dismissed because of a strong family history of breast cancer, according to news reports. The cases included women who had worked as air hostesses and as nurses, they noted.
One of the women who received compensation was Ulla Mahnkopf, who had worked for 30 years as a flight attendant on the Scandinavian airline SAS. In an interview with BBC Scotland, she said that after years of sleep disruption and jet lag, when she stopped work she felt as if she was "coming out of a shell." She was diagnosed with bilateral breast cancer.
Based on Epidemiologic Evidence
The Danish Board says these claims were recognized after the Occupational Diseases Committee discussed — in November 2007 — a review of the epidemiologic evidence between night-shift work and the risk for breast and other cancers.
"After these discussions, the Committee decided that breast cancer, after many years of night-shift work, qualified for recognition as an industrial injury," it explains on its Web site.
The next step is for the Board to review the work of the International Agency for Research on Cancer (IARC) in this field and to decide if breast cancer after night-shift work should be included on the list of occupational diseases.
The IARC, an agency of the World Health Organization, has recently classified shift work as a possible carcinogen.
In a statement released in December 2007, the IARC said that its expert working group had concluded that shift work that involves circadian disruption is "probably carcinogenic to humans," and it was ranked in group 2A, along with ultraviolet light radiation. This is below the group 1 category, which is "carcinogenic to humans," and includes asbestos, but above group 2A, which is "possibly carcinogenic to humans," and includes lead, the pesticide DDT (dichloro-diphenyl-trichloroethane), and engine exhaust.
"The level of evidence is really no different than it might be for an industrial chemical," Vincent Cogliano, PhD, of the IARC commented in a BBC news report.
The agency reached their conclusions after looking at a wide number of studies of both humans and animals, he explained. One of the studies (J Natl Cancer Inst. 2001;93:1563-1568) showed a 36% greater risk for breast cancer in women who had worked night shifts for more than 30 years than in women who had never worked nights.
Dr. Cogliano said there was evidence to support the hypothesis that alterations in sleep patterns could suppress the production of melatonin in the body. "Melatonin has some beneficial effects in preventing some of the steps leading to cancer," he explained.
However, 1 breast cancer expert has questioned the link to night-shift work. John Boyages, MD, director of the New South Wales Breast Cancer Institute, in Sydney, Australia, said he was not convinced. "I am a little bit puzzled, to be honest, about the compensation case, and I really think [the Danes] have gone out on a limb," he said in radio program from the Australian Broadcasting Corporation (ABC).
"My personal view is that it is a complex Rubik's Cube and we might be looking at this as a night-shift issue, but when you turn the cube the other way, it is probably obesity, it might be [hormone replacement therapy], it might be a lack of vitamin D, which would be my strong guess," he told ABC.
Dr. Boyages noted that there is a lot of research at present on vitamin D, and there have been reports suggesting a link between vitamin D deficiency and breast cancer, but the reason is still unclear. "All we do know at the moment is that the vitamin D receptor is intricately related to the estrogen receptor, and very close on the same gene, and we think the whole thing is all connected together."
However, another expert, Prof. Andrew Watterson, an occupational health specialist at Stirling University, in Scotland, said: "The Danish response to the breast cancer issue is very progressive."
"The British government should absolutely follow suit," he said in an interview with the Guardian newspaper.
There are no such plans at present in the United Kingdom, although an ongoing study by the Health and Safety Executive, due to be completed in 2011, is investigating the link between night-shift work and breast cancer.
"I think we can say there is a big public-health problem here," Prof. Watterson said. He noted that there is also convincing evidence linking night-shift work with prostate and uterine cancers, as well as other medical problems, such as gastric problems and colorectal cancer.
However, Kat Arney, PhD, senior science information officer at Cancer Research UK, argued that the link between breast cancer and night-shift work has not been conclusively shown. Although a number of studies have suggested a link, there are many other factors involved. For example, breast cancer occurs more commonly in women who are inactive, and women who work night shifts may get less exercise than the general population, she told the Guardian.
"At the moment, we don't know how other lifestyle factors — such as taking [hormone replacement therapy], obesity, having fewer children, and alcohol consumption — interact with shift work to increase a woman's risk of breast cancer," Dr. Arney told Sky News Online.
"Nor do we know how many years of shift work might have a significant impact on risk," she added. "Another problem is that most studies have only looked at specific occupations rather than shift workers in general."
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