« PC follies: Part 2 | Gene Expression Front Page | Shoes »
January 19, 2004

Lactose tolerance/intolerance

The truisms about lactose intolerance are so well known that people tend to not get into specifics. It can be hard to find specific information about the geographical extent of lactose tolerance. Here is some sites I found with info.

UC Davis Nutrigenomics:

The A haplotype conferring lactose tolerance has an 86% frequency in the northern European population, but only 36% in southern European populations.

Lactose intolerance rates as given on the above site:

Southeast Asians/98%
Asian Americans/90%
Alaskan Eskimo/80%
African Americans Adults/79%
Mexicans from rural communities/73.8%
North American Jews/68.8%
Creek Cypriots/66%
Mexican American Males/55%
Indian Adults/50%
African American Children/45%
Indian Children/20%
Caucasians of N. European and Scandinavian decent/5%

Another site highlights the importance of intra-regional differences:

The prevalence varies by race and ethnicity. It is more common among African-Americans, Hispanics and oriental population. In India, for example, it is seen in 25% of north Indian and 70% of south Indian population.

Here are some conclusions that might surprise:

A study of regional differences in prevalence of primary adult lactose malabsorption in Italy was conducted on 205 subjects. Their origin was determined by their grandparents' birthplace, 89 from northern, 65 from central, and 51 from southern areas of Italy...Prevalence of lactose malabsorption is significantly lower in the central sample (19%) than in the northern (52%) and southern (41%) samples (p less than 0.01). This finding contrasts with the hypothesis of a continuous increase in frequency of lactose malabsorption from northern to southern Europe and is probably due to the complex genetic history of the Italian population.

Finally, a more full treatment (follow the link for full text access):

The prevalence of primary lactose maldigestion is 35% in Scandinavia, 17% in Finland, 515% in Great Britain, 15% in Germany, 1520% in Austria, 17% in northern France, 65% in southern France, 2070% in Italy, 55% in the Balkans, 7090% in Africa (exeptions: Bedouins, 25%; Tuareg, 13%; Fulani, 22%), 80% in Central Asia, 90100% in Eastern Asia, 30% in northern India, 70% in southern India, 15% in North American whites, 80% in North American blacks, 53% in North American Hispanics, and 6575% in South America

I stopped drinking milk at the age of 5. People always assume I have lactose intolerance, and those in the "know" often ask in a way that it is obvious that it makes sense in light of the fact that I am non-European. Of course, the above data indicates that the situation is more complex than that. The old story about sending powdered milk to Africa and the problems that caused are held up to show the importance of biological considerations, but people often tend to gloss over the deeper details. If there was a famine among the Fulani of the Sahel, powdered milk would cause no problem, and these are the very people that are often the most affected by the desertification of the Sahara....

Posted by razib at 02:55 PM