Chronic inflammation is the modern day silent killer. It promotes the development of many deadly diseases, including cancer (http://www.scientificamerican.com/article.cfm?id=chronic-inflammation-cancer), heart disease, stroke, Alzheimer’s disease and diabetes (http://www.lef.org/protocols/health_concerns/chronic_inflammation_01.htm).
So, what is inflammation? Acute, or short term, inflammation is our normal response to an infection. The infected area becomes red, swollen and inflamed. We bring our innate immune system arms to bear, knocking holes in the bacterial cells, spewing out chemical poisons, and actually eating the enemy. A war against the infection is waged, and when it is won everything returns to normal.
Chronic, or long term, low level inflammation is, however, quite a different beast. The body is acting like it is constantly battling a low grade infection, even though generally none is present. And the effects can be lethal, as mentioned, promoting a host of diseases.
What causes chronic inflammation? There are several likely causes, including stress, obesity, diet, and in some cases actual chronic infection. But recent studies suggest a surprising correlation between an affluent lifestyle and chronic inflammation.
It has been known for some time that “being too clean can sometimes lead to disease.” (http://www.pbs.org/wgbh/rxforsurvival/series/diseases/polio.html). Polio, for example, existed for many centuries as a common virus, but rarely causing disease. Polio virus normally infects out intestinal tracts. It is transmitted by the “fecal-oral route”, when our poop contaminates our food. Before good sanitation procedures became common almost everyone carried the polio virus and infants would be infected at an early age. But the virus is quite benign when infecting infants, probably because of partial protection from the mother’s antibodies. So the severe form of the disease, where the nervous system is attacked resulting in paralysis, was uncommon. But in the 1900s, as the water supplies and sewage disposal systems became more sanitary, fewer people became infected with the virus, so sometimes the mother did not transmit protective antibodies, and infections at a much later age became more frequent. FDR was not infected until he was 39 years old. And at this age the paralytic form of polio is much more likely. So we paid a price for our improved hygiene.
A similar story might hold true for chronic inflammation. McDade et al (http://www.ncbi.nlm.nih.gov/pubmed/22639072) recently published a study in the American Journal of Human Biology where they examined chronic inflammation levels in the hinterlands of Ecuador, where very primitive living conditions prevailed. It is possible to quantitate chronic inflammation by measuring the blood levels of a protein, CRP, produced by the liver. They followed the CRP levels of the Ecuadorians for many weeks, finding that they have remarkably low levels of chronic inflammation. Of course their CRP levels went up when they had an infection, but their background CRP levels were about four times lower than what is seen in America. None of the Ecuadorians had CRP concentrations that would classify them as having chronic inflammation. This is in sharp contrast to America, where one third of adults have chronic inflammation, with CRP levels above 3 mg/l.
MacDade et al state that “infectious microbes have been part of the human ecology for millennia, and it is only recently that more hygienic environments in affluent industrialized settings have substantially reduced the level and diversity of exposure.” They suggest that natural exposure to microbes at an early age helps to fine tune our immune systems, “and in the absence of such inputs, poorly regulated or self-directed inflammatory activity may be more likely to emerge.”
So, when our immune systems aren’t presented with enough other things to attack, they might decide to attack us! It is probably not appropriate to start feeding our kids dirt, but it might be time to develop a safe soup of microbes, a kind of probiotic for infants, that could help them to mold their immune systems, and to reduce the levels of chronic inflammation in coming generations.