We’ve grown up with the idea that dirt is bad. If you drop food on the floor, don’t dare to pick it up and eat it. Sanitize your kitchen and bathroom with “germ killers.” Filter your water. Purify your air. Sterilize your babies’ bottles. Well, maybe all that attention to fastidious cleanliness isn’t serving us so well. Maybe our immune system needs the exercise of dealing with microbes.
Enter the “hygiene hypothesis.” Proponents maintain that if our immune system is deprived of the targets it has evolved to deal with, namely microbes, then it turns its weapons on whatever target is available, even if this target is not dangerous. That target may be a protein in peanuts or an ingredient in a perfume. Immune reactions often involve inflammation as the body rushes white blood cells to the site of a perceived attack by an intruder. Sometimes inflammation can become chronic and may even be implicated in diabetes, heart disease and strokes. Indeed a study in the Philippines, where sanitation is not what we are used to here, showed that the more disease-causing microbes children were exposed to when they were young, the lower their blood levels of a marker of inflammation known as C-reactive protein by the time they reached the age of twenty. A rise in C-reactive protein is not a good thing; it has been linked with heart disease and diabetes. Every episode of diarrhea before the age of two cut the chance of a higher CRP later by 11% and every two months spent in a place with animal feces cut it by 13%. Being born in the dusty, dirty, dry season cuts the chance of later elevation of CRP by thirty percent. Somehow it seems that early exposure to germs reduces the risk of chronic inflammation later in life.
And now it seems, such exposure may even reduce the risk of cancer. As strange as it may seem, dairy farmers who have to shovel manure all the time, and breathe aerosolized manure dust, have a five times lower rate of lung cancer than the general population. And it is specifically dairy farmers. Colleagues who work in the fields and orchards don’t get this benefit. And it seems the greater the number of cows they work with, the greater the protection. Manure contains complex molecules composed of fats and carbohydrates called endotoxins. These are produced by bacteria but they are actually not dangerous. However endotoxins are recognized by the immune system as bacterial products and are used by the immune system to zero in on the bacterial target. Exposure to endotoxins apparently revs up the immune system and gets it ready to attack cancer cells which are targeted because they produce endotoxin-like compounds.
This argument is supported by an examination of cancer rates among female cotton textile workers in China. Cotton dust contains lots of endotoxin, and it turns out that women with higher and longer endotoxin exposure had a lower incidence of lung, breast, liver, stomach and pancreatic cancer. And then we have the interesting story of children in daycare. Statistics show that children who are in daycare during their first few months of life are less likely to develop leukemia or Hodgkin’s lymphoma as young adults. Studies have also shown that people who received a tuberculosis or smallpox vaccine as children have a lower risk of developing melanoma. Vaccines of course work by boosting the immune system. So the theory that seems to be developing is that cancer occurs when the immune system doesn’t recognize cancer cells as dangerous because it has not been programmed properly in early life by exposure to a variety of microbes. An interesting theory, of course in need of further proof. Who would have ever thought that the answer to cancer may lie in shoveling some poop?