Tuesday, May 09, 2006

Hygiene Hypothesis - Part 1 - What is it?

I'd guess about 80% of what I blog about is stuff in which I have no idea what I'm talking about. So. I've decided to write a multi-part series discussing one of my current interests - The Hygiene Hypothesis.

The Hygiene Hypothesis was formally proposed, in the British Medical Journal, by Dr. David P. Strachan in 1989 (Strachan, DP. Hay fever, hygiene and household size. BMJ 299:1259-60). Dr. Strachan observed, as have many others, that hay fever and other allergies occur more often in smaller, more affluent families.

He suggested: "These observations could be explained if allergic diseases were prevented by infection in early childhood, transmitted by unhygienic contact with older siblings, or acquired prenatally...Over the past century declining family size, improved household amenities and higher standards of personal cleanliness have reduced opportunities for cross infection in young families. This may have resulted in more widespread clinical expression of atopic disease."

Put more simply The Hygiene Hypothesis states that growing up in a relatively clean environment may make you more more likely to suffer from allergies and other autoimmune diseases. This is opposed to growing up on a farm, having many siblings, pets or attending day care during your first year of life. Some of us would like to argue that it has to do with whether you are harboring intestinal nematodes or not.

The increased incidence of allergies and autoimmune diseases is relatively recent, within the last 50-60 years. This means that something that protected us from allergies and autoimmune diseases has been lost from the childhood environment over recent decades. What is the something? Well, it should be something that has been present throughout the evolution of the mammalian immune system and it should be something that has been progressively depleted from the environment of developed countries over the last 5-6 decades.

One thing that has definitely been lost, at least in the United States and Canada, is intestinal nematode infection. Worms!

1 comment:

Sara said...

Too funny that you blogged this today b/c we were just discussing this theory in lectures today . . . the Med Para students were not understanding that maybe worms can be good for you. Quentin said, "be sure to get your children their annual does of worms" Now how often do you hear that sorta statement??