( 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 would n'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 .
Danish women who got breast cancer after night shift get treated . They should have worked at least one night a week for 20 to 30 years . WHO have concluded that working night shifts ` ` probably causes cancer ''