Thursday, February 07, 2008

Has Technology Made Us So Clean That We’re Sick?

In Technology Challenged I wrote about the impact of water supply, sanitation, and hygiene technology. The chapter on how technology has changed us described how this technology has improved human health and lifespan dramatically. The World Health Organization estimates its absence was responsible for 88% of the 1,800,000 deaths from diarrhoeal disease in 2004.

Sure, water supply, sanitation, and hygiene technology have benefits, but anyone who’s read Technology Challenged will note that technology almost invariably has both, too. So, what are the costs of these technologies?

A study comparing incidence of asthma and allergies in the former East and West Germanys, found children much less affected in East, where health care was poorer and pollution greater. Other studies have also suggested this correlation, now called the hygiene hypothesis, which suggests that a cleaner environment—treated water, hand-washing, vacuum cleaners, indoor floors not made of dirt—could lead to asthma, allergies, and autoimmune diseases. How might that work?

In Riddled with Life, Marlene Zuk describes our relationship with parasites, including those that rely on water to move from host to host. She offers a mechanism for causality behind the hygiene hypothesis:

Exactly what is it about early stimulation by bacteria, viruses, or other parasites that keeps the immune system calm in the face of harmless entities like pollen or ones own intestinal cells? Obviously the analogy of immune system cells being like bored unemployed workers that make mischief on the rest of the body is just that, an analogy, and even the most anthropomorphic among us stops short of assigning personality traits to bone-marrow products. The more accurate answer seems to lie in a characteristic of the immune system. Part of our response to foreign invaders of the body is mediated by a kind of white blood cell called a T cell. The T cells come in a variety of types, including killer T Cells and helper T cells. The helper T cells in turn are also divided into two types, called Th-1 and Th-2. The Th-1 and Th-2 responses are responsible for protection against different things, with the former concerned with bacterial and viral diseases and the latter with infections by worms and other large parasites. Each type of helper T cell produces a different set of chemical messengers used to regulate inflammatory response like tissue swelling and the production of mucus. These chemicals interact with each other and keep the entire system in balance.

In countries with scrupulous hygiene, where children are vaccinated and antibiotics are widely administered, the low level of Th-1 stimulation results in an increase in the Th-2 response. These Th-2 responses trigger an exaggerated mucus production and contraction of muscles in the airways, which can in turn cause allergic diseases and asthma. In countries where bacteria, worms, and other pathogens are abundant but vaccination and antibiotic levels are low, the Th-2 responses are activated, but they are regulated by repeated cycles of infection and inflammation, with the inflammation countered by natural antiallergic reactions. Thus they rarely escalate out of control as much as Th-2 responses in people from the industrialized areas. The immune systems of people from less developed countries still respond physiologically to allergens like pollen or house dust mites, but the people do not go on to develop a disease. It is as if the Th-2 arm learns to recognize an innocuous but foreign substance for what it is, and has a blasé “been there done that” reaction to it, rather than spiraling into a panicky cycle of swollen tissue and dripping glands. [pp. 46-47]

Where technology introduces a problem, there’s often a new technology invented to correct it (and then a newer technology to correct its problems). In this case, we have a story that will be hard to forget. A treatment for Crohn’s Disease, which may be an autoimmune reaction more common among those free of parasitic worms, is parasitic worms.

So that the cure not be worse than the disease, patients were given tiny “pig whipworm” eggs, thousands of them mixed with Gatorade. Evolved to thrive in pigs’ colons, not the foreign and hostile human colon favored by a different species of whipworm, these reluctant pioneer worms could do little more than hatch, provoke a Th-2 response that regulated the patient’s Th-1 activity, and then die and pass out of the patient’s colon. In early tests (not double-blind with control groups), patients showed remission or improvement. More important, worms caused none of the hair loss / swelling / nausea side effects of the drugs used to treat Crohn’s Disease. Presumably the worms suffered no hair loss either.

Much more common than Crohn's Disease are stomach ulcers. The Nobel Prize in medicine went to the doctors that identified the bacterium Helicobacter pylori as responsible. Stress might exacerbate stomach ulcers, but the bacterium were the cause, allowing us to take antibiotics, kill the H pylori, and return to our stressful lifestyles. Not so fast! A 2007 study showed that H pylori helps to protect us against asthma and may play an important role in the development of the human immune system, preventing immune hyperreactivity. H pylori may be joining the legion of life that technology enables us to render extinct:

The key point, says Dr Blaser, is that H pylori colonization is the default human state of affairs, but it's a default position we're fast drifting away from. "About 10% of the US population now has detectable H pylori colonization. I was just in Sweden and Germany, where I'm told the figure is less than 5%. The proportion in the developing world is over 50%, and just a few generations ago the levels in our own societies were 70, 80, even 90%. So H pylori is disappearing really fast, and this disappearance is almost certainly mirrored in other microorganisms we can't detect as easily."

I am appreciating how multifaceted the costs and benefits of technology can be. Our bodies are complex systems that can react long after an exposure…or only to combinations of exposures. The same is true for the ecosystems in which we live, making it challenging to link cause and effect. Helping us evaluate our technologies is an important challenge to our investigative and modeling technologies.

I will blog more on this later, as I have been reading books on chemicals and disease. Perhaps not surprisingly, I am still seeking those who, like me, find this subject perfect for cocktail party conversation and pleasure reading.

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