Milk and Asian people

Lactose intolerance is the inability to metabolize lactose, a sugar found in milk and other dairy products, because the required enzyme lactase is absent in the intestinal system or its availability is lowered.

It is estimated that 75% of adults show some decrease in lactase activity during adulthood worldwide. The frequency of decreased lactase activity ranges from nearly 5% in northern Europe to more than 90% in some Asian and African countries [1]

Primary lactose intolerance. Environmentally induced when weaning a child in non-dairy consuming societies.[3] This is found in many Asian and African cultures, where industrialized and commercial dairy products are uncommon.

The normal mammalian condition is for the young of a species to experience reduced lactase production at the end of the weaning period (a species-specific length of time). In non dairy consuming societies, lactase production usually drops about 90% during the first four years of life, although the exact drop over time varies widely.[8]. The majority of the world’s human population follows this trend, with the lactase producing genes largely inactivated in adulthood.[9][1]

Some cultures, such as that of Japan, where dairy consumption has been on the increase, demonstrate a lower prevalence of lactose intolerance in spite of a genetic predisposition[10].

Lactose Intolerance Survey:

Northeastern Han Chinese: 92.3%
Chinese: 93%
Southeast Asians: 98%
Thais: 98%

Lactose intolerance levels also increase with age.

It is not surprising then, that consuming milk products became an important part of the agricultural way of life in the Neolithic. It is believed that most of the milk was used to make mature cheeses which are mostly lactose free.[citation needed]

Roman authors recorded that the people of northern Europe, particularly Britain and Germany drank unprocessed milk (as opposed to the Romans who made cheese).[citation needed] This corresponds very closely with modern European distributions of lactose intolerance, where the people of Britain, Germany and Scandinavia have a good tolerance, and those of southern Europe, especially Italy, have a poorer tolerance.[34]

In east Asia, historical sources also attest that the Chinese did not consume milk, whereas the nomads that lived on the borders did. Again, this reflects modern distributions of intolerance. China is particularly notable as a place of poor tolerance, whereas in Mongolia and the Asian steppes horse milk is drunk regularly. This tolerance is thought to be advantageous as the nomads do not settle down long enough to process mature cheese. Given that their prime source of income is generated through horses, to ignore their milk as a source of calories would be greatly detrimental.

Source: http://en.wikipedia.org/wiki/Lactose_intolerance