Lactose intolerance is seen mainly in people of cultures that don't consume milk regularly after weaning. Like the Chinese in China, they stop drinking milk after weaning from mother's milk. Americans have a dairy culture, they never stopped consuming dairy until they die.
When a person stops consuming dairy for a long time, the digestive system stops or slows down producing lactase, an enzyme that digests lactose, a milk sugar. Undigested lactose is what causes lactose intolerance.
Milk and milk products were not common food items in the past there, but recently dairy consumption has increased greatly because of better economy. Dairy production was rare in China, even today's is very small, much of the dairy products available in China are imported.
Lactose intolerance is not a natural sign of human digestion, it's caused by violation of nature. Nature designed humans to continue to consume milk and milk products, the probiotics in them are very important to health in the human body. It has been known for a long time that dairy-based probiotics have benefits on health. Science discovers dairy-based probiotics are very critically important to immune system. People who consume no dairy or little dairy that contains good probiotics have higher rate of health problems.
Read this article: Probiotics and Milk:
livestrong.com/article/292202-probiotics-and-milk/
