(CNN) -- Employers in Denmark have started paying compensation to women who have developed breast cancer after working night shifts.
Studies have shown that nurses working night shifts have an increased risk of developing breast cancer.
Thirty-eight eight women have so far received payments via their employers' insurance companies, the Danish National Board of Industrial Injuries told CNN.
To qualify for compensation, women must have developed breast cancer after having worked at least one night shift a week for 20 to 30 years.
The amount of compensation depends on the severity of claimants' illness and their ability to work.
The move came after the International Agency for Research on Cancer (IARC), part of the World Health Organization, concluded that night work is "probably carcinogenic to humans," in October 2007.
Ulla Mahnkopf developed breast cancer after 30 years working as a flight attendant for SAS, a job where night shifts were the norm.
She told the BBC that had she known the effects of night working she wouldn't have flown for so many years.
The IARC classifies the cancer risk of night work as "Group 2A" -- the same as using sun beds -- and just one group below confirmed carcinogens like asbestos and mustard gas.
The IARC reviewed published scientific literature and found that long-term night workers have an increased risk of breast cancer.
Dr Vincent Cogliano, Head of the IARC Monographs Program, told CNN that the evidence in humans is limited to breast cancer because researchers have historically studied nurses and flight attendants.
Cogliano said he would like to see studies carried out on different types of workers in other industrial settings.
He added that the human studies are consistent with laboratory research that exposes animals to changing patterns of light and dark to mimic the conditions of humans working at night.
It is thought that night work can disrupt the circadian system, which can alter sleep patterns, suppress melatonin production, and affect genes involved in tumor development.
"This is a very important topic and it needs more research," said Cogliano.
"Working at night or disrupting your sleep cycle is a widespread phenomenon and it is important to understand the health implications. There could be other cancers or other health implications involved."
Those most likely to do night shifts are those working in the health-care industry, hospitality, industrial manufacturing, news media and security workers.
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