IMPORTANT NOTICE ABOUT COMMENTS

Because of spam, I personally moderate all comments left on my blog. That means you will not see your comment when you post it. It will instead show up within 48 hours, along with my response if one is appropriate.

All comments are welcome and will be posted, even if they are negative. You just can't promote other sites or products in them.

If you have a personal question about LI or any related topic you can send me an email at stevecarper@cs.com.

Otherwise, this blog and my Lactose Intolerance Clearinghouse are now legacy sites, meaning that I am not updating them any longer. The basic information about LI is still sound. However, product information and weblinks may be out of date.

My old website can be found at www.stevecarper.com/li

For quick offline reference, you can purchase Planet Lactose: The Best of the Blog as an ebook on Smashwords.com or Amazon.com or BarnesandNoble.com or a whole lot of other places that Smashwords is suppose to distribute the book to. Almost 100,000 words on LI, allergies, milk products, milk-free products, and the genetics of intolerance, along with large helpings of the weirdness that is the Net.

Friday, December 23, 2005

Lactose Intolerant? Blame Your Ancestors

I've said this before, mainly in my book - Milk Is Not for Every Body - but whether you are or aren't lactose intolerant depends mostly on whether your ancestors were.
And your ancestors' decision whether or not to domesticate milkable animals for dairy products led to the spread of the mutation that allows for lactose tolerance all through adulthood.

More confirmation of this comes from the work of evolutionary biologist Paul Sherman, a professor of neurobiology and behavior at Cornell University. His work appeared in a recent issue of Evolution and Human Behavior, but I'm going to spare you and just quote from an article about it, written by Michael Kanellos at CNET News.


Researchers at Cornell University have shown in a recent study that lactose intolerance is largely a factor of cultural evolution. That is, members of ethnic groups that emerged in regions where raising cattle was common often are more genetically predisposed to digest milk products. Meanwhile, people whose ancestors came from regions where extreme temperatures, short growing seasons and dangerous animal-borne diseases made animal husbandry expensive and difficult often feel cramped and nauseous after eating dairy products.

In cheese-happy Denmark, for instance, only 2 percent of the population studied was lactose intolerant. In Zambia, near the equator, 100 percent of the individuals studied were lactose intolerant.

"The implication is that harsh climates and dangerous diseases negatively impact dairy herding and geographically restrict the availability of milk, and that humans have physiologically adapted to that," Sherman said.

The key to lactose intolerance is the enzyme lactase, which is required to digest milk. Although infants around the world produce the enzyme, more than half the people in the world, particularly those of Asian and African descent, stop producing it as they mature. People of northern European descent tend to continue to produce the enzyme because of a genetic mutation, according to Sherman. Thus, they can drink milk throughout life.


The full journal article can be found at Bloom, G. and P.W. Sherman. 2005. Dairying barriers and the distribution of lactose malabsorption. Evolution and Human Behavior 26:301-312.

Bookmark and Share

No comments: