Lactose Intolerance Linked To Ancestral Environment (2005)

[Felix the Cat]

http://www.sciencedaily.com/releases/2005/06/050602012109.htm

ITHACA, N.Y. -- Got milk? Many people couldn't care less because they can't digest it. A new Cornell University study finds that it is primarily people whose ancestors came from places where dairy herds could be raised safely and economically, such as in Europe, who have developed the ability to digest milk.

On the other hand, most adults whose ancestors lived in very hot or very cold climates that couldn't support dairy herding or in places where deadly diseases of cattle were present before 1900, such as in Africa and many parts of Asia, do not have the ability to digest milk after infancy.

"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," said evolutionary biologist Paul Sherman, a professor of neurobiology and behavior at Cornell. "This is a spectacular case of how cultural evolution -- in this case, the domestication of cattle -- has guided our biological evolution."

Although all mammalian infants drink their mothers' milk, humans are the only mammals that drink milk as adults. But most people -- about 60 percent and primarily those of Asian and African descent -- stop producing lactase, the enzyme required to digest milk, as they mature. People of northern European descent, however, tend to retain the ability to produce the enzyme and drink milk throughout life.

Sherman and former Cornell undergraduate student Gabrielle Bloom '03, now a graduate student at the University of Chicago, compiled data on lactose intolerance (the inability to digest dairy products) from 270 indigenous African and Eurasian populations in 39 countries, from southern Africa to northern Greenland. Their findings will be published in a forthcoming issue of Evolution and Human Behavior.

On average, Sherman and Bloom found that 61 percent of people studied were lactose intolerant, with a range of 2 percent in Denmark and 100 percent in Zambia. They also found that lactose intolerance decreases with increasing latitude and increases with rising temperature, and especially with the difficulty in maintaining dairy herds safely and economically.

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 morning sickness occurs.

"Both appear to serve an important function to protect the individual," Sherman said. "Spices contain antimicrobial compounds, and they may be used to destroy food-borne pathogens, especially in hot climates. Nausea and vomiting early in pregnancy also may protect women and their embryos from food-borne pathogens and other toxins."

A Darwinian medicinal view complements traditional medicine, Sherman said, because if researchers can better understand why a symptom occurs, such as a fever, runny nose or allergy, they can better evaluate whether it is best to eliminate or tolerate it.

[Felix the Cat]

http://www.foodnavigator.com/news/ng.asp?id=42796-scientists-identify-lactose

A single genetic mutation allows people to tolerate milk after they leave babyhood, and is virtually the same in people of Asian, European and African descent, researchers reported Sunday.

Finding the tiny change in the genetic code should allow scientists an easy test for lactose intolerance, a painful digestive condition, and also offers insights into how some groups of people evolved a milk-drinking culture, the team of U.S. and Finnish researchers said.

People who have lactose intolerance — most of the people in the world — cannot digest large amounts of lactose, the main sugar found in dairy products.

If they eat milk, cheese or other dairy products they develop nausea, cramps, bloating, gas and diarrhea. Between 30 million and 50 million North Americans are lactose intolerant — 75 per cent of African-Americans and 90 per cent of Asian-Americans.

It affects about 5 per cent of Northern Europeans and close to 100 per cent of Southeast Asians, said the researchers, who reported their findings in the journal Nature Genetics.

Lactose intolerance was known to be genetic, caused by a recessive gene, meaning that a person has to inherit a “faulty” copy from each parent to be lactose intolerant.

“This is the first time this mutation, the DNA change, is actually identified,” said Dr. Leena Peltonen, a geneticist at the University of California Los Angeles, who led the study. “This paves the way to DNA testing.”

Peltonen and colleagues first looked at nine Finnish families, 196 people, who had lactose intolerance. They narrowed it down to a gene that regulates the gene responsible for making the enzyme that breaks down lactose.

They found two changes, one in every person with lactose intolerance and another in all the Finns.

Then they looked at blood samples from nine Italians, nine Germans and 22 Koreans, all of whom had been diagnosed with lactose intolerance, as well as genetic information from 109 people from Utah in the United States and France.

They found the gene variation in 41 per cent of the French, 7.6 per cent of white North Americans and 79 per cent of African-Americans.

Peltonen said babies are born with the ability to digest lactose — it is found in breast milk - but they lose this ability after weaning.

“That we found the same DNA variant in all lactose-intolerant people across distant ethnic groups indicates to us that it is very old,” she said.

“We believe that the variant we identified in patients is the original form of the gene, which mutated to tolerate milk products when early humans adopted dairy farming,” she added.

“This 'lactose intolerance' today is actually the ancient form of the gene.”

In cold climates where winter crops cannot be reaped, a gene mutation allowing adults to digest milk would help people survive better. People who survived would pass on those genes to their offspring.

“Ten to twelve thousand years ago, when human populations started to use dairy culture — cattle, goats — around that time the mutation happened and made some individuals lactose tolerant,” Peltonen said.

“I think it's fascinating. People think lactose intolerance is a disease, but this is how everyone was initially.”

[Felix the Cat]

http://www.scienceinafrica.co.za/2002/june/lactose.htm

Last month's article on cow's milk and the problems which can be associated with it was packed full (to use the advertising jargon for milk) of interesting information. But we were rather startled to see lactose intolerance - which affects a majority of the world's population - described as a "disease". In fact, it is adult lactose tolerance for cows' milk that is unusual. We thought that curious readers might be interested in why this is so.

In his article Milk Allergy and Lactose Intolerance (May 2002), Dr Steinman gives the following figures for lactose intolerance for children over 5 years old: "90-95% of black individuals and 20-25% of white individuals throughout the world". In fact, the picture is much more complicated. Many Asian populations, especially people from Far East, have rates of lactase deficiency approaching 100%. Additionally, there are a few groups in Africa, such as the Fulani, who have relatively low rates of lactose intolerance (around 20-25 percent). Conversely, some European populations like the Swedes are almost completely lactose tolerant (apx. 4% deficiency). Given that most of the world does not fall neatly into 'black' or 'white' categories, such variation is important. In fact, the world average for lactose intolerance is probably much closer to the 90-95% range given for 'blacks.' Therefore, we were very surprised to see this condition described as a "disease". Elsewhere we have seen it described as a "disorder". Why should this be when most adults in the world are lactose intolerant, clearly making this the normal adult condition? The perception of lactose intolerance as a health problem is a rather narrow Western view. We imply no offence to Dr Steinman, as this perspective is widely held, and in general misconceptions about the healthy associations of whole dairy milk are widespread and probably have a lot to do with marketing and advertising campaigns.

As the figures show, whole cow's milk is definitely not for everyone, at least not unless the milk is soured or fermented, as explained by Dr Steinman. Human infants, like other mammals, receive nourishment from mother's milk. Infants have an enzyme that allows milk sugar - lactose - to be digested. In most human populations, the manufacture of the lactase enzyme is "turned off" by around four years of age. The same is true of other mammals, which become lactose intolerant following weaning. The really interesting question, then, is why are some humans not lactose intolerant? And why are relatively few 'white' people - aka. of Western European origin - lactose intolerant?

The answer lies somewhere in the past. Human beings only began to cultivate domestic grains and keep domestic animals relatively recently. Sheep and then cattle were first domesticated just over 10 000 years ago, in the Near East where the wild progenitors of these animals lived. Grains like wheat and barley were also domesticated at around this time. All of this took place through selective breeding - and consequent genetic manipulation - with humans in control. It brought about a quantum change in the way that people lived - they settled down, cultivated most of their food and populations began to grow. Not all of the change was for the better, as amongst other new problems humans also began to inherit diseases from their animals and from close proximity to large numbers of people (like TB and other infectious diseases - but that is another story!). The new way of life spread, along with the cattle, sheep and grains, reaching Western Europe a few millennia later.

It was here in Western Europe that some populations began an evolutionary transition to lactose tolerance. This meant that in certain individuals, as a result of genetic change the enzyme allowing the digestion of milk sugar continued to be produced throughout adult life. So these individuals no longer lost their childhood lactose tolerance but carried it into adulthood. This mutation also occurred in the Fulani people in the Sahel, although somewhat later since domesticated cattle reached this area just a couple of millennia ago.

Lactase deficiency is a classic anthropological example of a genetic trait that has been influenced by cultural factors. There is a relationship between the frequency of lactase deficiency in a population and whether or not the population was involved in intensive dairy farming. Low levels of lactase deficiency are found in European populations with a long history of dairy farming, and highest levels in populations of Asian ancestry who were not dairy farmers. Low levels also occur in other populations that rely extensively on milk in their diet (like the Fulani of Western Africa, and it is believed, Khoi pastoralists of Southern Africa). These numbers suggest that the ability to digest whole milk later in life is selected for in environments where milk is a major source of nutrition and forms an important part of the diet. Genetic change resulting in lactose tolerance presumably carried strong advantages in such circumstances - i.e. in helping people to survive longer and to reproduce themselves.

This transition to lactose tolerance seems to have been most 'successful' (in evolutionary terms), in Western Europe. When Western Europeans began to colonise other areas of the world from the 16th century onwards, the lactose tolerance 'gene' travelled along with them, no doubt increasing the frequency of lactose tolerance in contact populations across the colonised world.