Fighting cancer with filth

[Guest guest]

Fighting cancer with filth

a.. 12 January 2008

b.. From New Scientist Print Edition. .

c.. Marshall

IT WOULD be wrong to call dairy farming a shit job. But workers on dairy farms

do have to deal with vast quantities of manure. In fact, they inevitably end up

breathing in a lot of dust consisting largely of dried manure, along with all

the bacteria that grew in it. That sounds unhealthy, and in some ways it is, but

it does have one benefit: dairy farmers are as much as five times less likely to

develop lung cancer.

As strange as it sounds, epidemiologists are starting to uncover some unexpected

links between our exposure to dirt and germs, and our risk of cancer later in

life. Children who attend daycare in their first few months are much less likely

to develop leukaemia than those who stay at home, for instance, while some

tuberculosis vaccines reduce the risk of skin cancer. Such findings point

towards a curious possibility: one way to avoid dying of cancer may be a hefty

dose of germs.

The notion that living dirty has benefits may ring a bell. Researchers have been

debating the " hygiene hypothesis " for years, but it is typically discussed as an

explanation for the rising incidence of allergies and asthma in developed

countries, not cancer. The idea is that our immune systems evolved to conduct a

ceaseless war on pathogens, parasites and other microbes, but modern lifestyles

mean we face fewer threats. This throws our immune systems out of kilter, making

them prone to overreact to certain stimuli like pollen or peanuts.

Now 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. 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.

This might seem surprising, given that some viruses can undoubtedly cause

cancers. Yet with a few childhood cancers it has long been suspected that the

risk of developing them is reduced by exposure to infections early in life.

Recent studies have confirmed that children who have social contact outside the

home early on, such as attending daycare, have a reduced risk of both childhood

leukaemia and Hodgkin's lymphoma as young adults. Others have found that kids

with more older siblings have less chance of developing Hodgkin's lymphoma, says

Ellen Chang of the Northern California Cancer Center in Fremont, who carried out

some of the studies.

It is not just childhood exposure that matters, though. As long ago as the 1970s

it was noticed that workers in cotton factories have surprisingly low rates of

lung and some other cancers. One explanation is that they owe the favour to

cotton dust. This contains lots of endotoxin, a lipopolysaccharide found in the

cell walls of many bacteria, which might keep the immune system on high alert.

A series of recent studies by Harvey Checkoway at the University of Washington,

Seattle, supports this idea. His team looked at cancer rates among female cotton

textile workers in Shanghai, China, where detailed records reveal past exposures

to endotoxin. Those with higher and longer endotoxin exposure on the job had a

lower incidence of many cancer types, including lung, breast, liver, stomach and

pancreatic cancer.

Endotoxin could also explain the reduced risk of lung cancer among dairy farmers

found by several studies in various countries. For instance, Giuseppe

Mastrangelo of the University of Padua in Italy and colleagues found that dairy

workers in the province were far less likely to get lung cancer compared with

their peers who worked in fields or orchards (Indoor and Built Environment, vol

13, p 35). The greater the number of cows, the greater the protection. Even

smokers gained some protection: smoking dairy farmers were less likely to get

lung cancer than smoking non-dairy farmers.

Full story

http://www.newscientist.com/article.ns?id=mg19726381.700 & print=true