A Danish decision last week which linked night working and breast cancer has received a very cool reception from interest groups here. RONAN MCGREEVYreports
EARLIER THIS month, the National Board of Industrial Injuries in Denmark made a decision which could have profound implications for women who work night shifts and for their employers.
The board decided that 37 women in Denmark, who worked night shifts, mostly flight attendants and nurses, won the right to compensation of up to €135,000 because they had all developed breast cancer.
The board based their awards on scientific studies which suggest that sleep disruption causes the body to produce less melatonin. The studies found that melatonin, which is produced when we sleep, reacts with a nutrient called linoleic acid which is a fatty acid found in food such as fish oils and which promotes healthy hair and the quick healing of wounds.
Linoleic acid is also thought to promote the growth of cancer cells. Researchers believe that melatonin inhibits linoleic acid from entering tumour cells and therefore slows their growth.
Studies carried out in the United States on rats showed that when they were exposed to constant light, tumours grew much quicker.
Denmark decided in November 2007 to consider financial compensation for women who had done night work over a period of 20-30 years and had breast cancer based on international studies.
It is now considering whether breast cancer should be on the list of work-related illnesses, a decision which, if implemented, could have worldwide implications for women who work night shifts.
The Danish authorities are now waiting for a report from the International Agency for Research on Cancer (IARC) on recent studies on the subject before making a final decision.
The news has caused a degree of concern and consternation around the world.
Oncologist Prof John Crown said designating night-shift working as an occupational hazard would be a “disaster” especially for hospitals which depend mainly on female nurses for staffing at night.
However, he said the designation had not been confirmed and was not based on any rigorous scientific appraisal.
“Rushing to judgment to say that working nights is a definite cause of breast cancer is probably premature,” Prof Crown said.
“There are a number of potential explanations as to why people who work nights might be more prone to this disease. The statement in the judgment that the ladies must have had their cancer caused by working night because they had no other risk factor is not correct.
“Most patients with breast cancer have no recognisable risk factor.”
The Marie Keating Foundation pointed out that the Health and Safety Executive in the UK commissioned a full analysis of the evidence involved which is due to be completed in 2011.
Foundation chief executive Lillian McGovern said there was “no conclusive evidence” to link night-shift working to breast cancer.
She said there were other lifestyle factors such as taking HRT, having fewer children and alcohol consumption which could be factors involved with getting breast cancer.
“Nor do we know how many years of shift work might have a significant impact on risk. Apparently, studies undertaken have only looked at specific occupations which limits the conclusions,” she said.
Instead, she has advised women to wait until the conclusion of the UK HSE study before making judgment and to remain breast aware in the meantime.
Similar sentiments were expressed by Irish Cancer Society spokeswoman Jane Curtin who said the IARC preliminary results needed more work.
“We would need to better identify what it is about the occupations of shift workers that may increase their risk of breast cancer so that we can recommend how they can guard against such risk,” she said.
She said there were a number of complicating factors in the study of lifestyle and breast cancer risk including ageing, having children late in life, not breastfeeding, being overweight and taking either the pill or large doses of HRT which need to be factored in before any definitive conclusions are reached.
“We would also need to investigate how these secondary risk factors interact with shift work and increase the risk of developing breast cancer,” she said.
MEP Kathy Sinnott said the conclusions of the Danish authority were backed up by research carried out by the World Health Organisation which declared night work a probable carcinogen and by the American Cancer Association which has put working at night into the company of UV radiation and anabolic steroids as risk factors for cancer.
Mrs Sinnott said: “It is important that employers and employees should be conscious that there are risks associated with night work.
“This should be taken into consideration when developing rotas and particularly when employees have other additional risk factors for cancer. The lesson here is that no person should be kept on night work for extended periods of time.”