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Working with large amounts of manure could be beneficial to dairy farmers, scientists say.
New Scientist magazine reports dairy farmers are five times less likely than the general population to develop lung cancer.
It says farmers typically breathe in a lot of dust consisting largely of dried manure, with all the bacteria that grow in it. "As strange as it sounds, epidemiologists are starting to uncover unexpected links between our exposure to dirt and germs, and our risk of cancer later in life."
The article argued that just as children who are exposed to germs from a young age are less likely to develop leukaemia, adults who have a greater exposure to germs than usual might build up a greater resistance to bugs, and even cancer.
"Some researchers are starting to wonder whether the higher incidence of certain cancers in affluent populations - including breast cancer, lymphoma and melanoma - might also have something to do with sanitised, infection-free living," it said.
"If they're right, the implications are huge. If we can understand exactly what it is about some germs that has a protective effect, we should be able to reduce people's risk of developing certain tumours later in life by exposing them to harmless microbes."
New Scientist said studies in Italy, Germany and France had shown a link between inhaling cow manure and the reduced risk of lung cancer, but breathing in dung was not the only way to cut the risk of cancer.
It said certain childhood vaccines could also do the trick, at least for melanoma, and it was possible that a variety of vaccinations or diseases could reduce cancer risk.
Dr Mike Berridge of the Malaghan Institute of Medical Research in Wellington said the report might not be entirely relevant to farmers here.
"I've been aware of some studies on asthma and farm workers but this one is a bit out of the blue. I'd be very surprised if it is the case," he said.
"It's very different overseas because they keep animals in barns and out of the weather and they don't have outdoor farming. I suspect something like that would be more relevant to European farm workers than New Zealand farm workers."
