A major challenge in interpreting the data, Sherman noted, was to resolve the puzzle that about 13 lactose-tolerant populations live side-by-side with lactose-intolerant populations in some parts of Africa and the Middle East.
"The most likely explanation is nomadism," Sherman concluded. All 13 of the populations that can digest dairy yet live in areas that are primarily lactose intolerant were historically migratory groups that moved seasonally, Sherman said. Their nomadism enabled them to find suitable forage for their cattle and to avoid extreme temperatures. "Also, the fact that these groups maintained small herds and kept them moving probably reduced the pathogen transmission rate."
According to the National Digestive Diseases Information Clearinghouse, some 30 million to 50 million Americans are lactose intolerant, including up to 75 percent of African Americans and American Indians and 90 percent of Asian Americans. Common symptoms include nausea, cramps, bloating, gas and diarrhea that begin about 30 minutes to two hours after eating or drinking foods containing the milk sugar lactose. The use of lactase enzyme tablets or drops or lactose-reduced milk and similar products can help the lactose intolerant digest dairy products.
Sherman's study concludes that adults from Europe can drink milk because their ancestors lived where dairying flourished and passed on gene mutations that maintain lactase into adulthood. The research, he said, is an example of Darwinian medicine, a new interdisciplinary field of science that takes an evolutionary look at health, and considers why, rather than how, certain conditions or symptoms develop. Sherman, for example, recently investigated why spices are used and why mor
Source:Cornell University News Service