"Milk can wake up the tired," says an advertising slogan from the dairy industry. Doctors and nutritionists believe that milk and dairy products can prevent potential bone shrinkage in old age. People have been advocating for the "School Milk Nutrition Program" (which has been shelved due to a lack of funding) in order to supplement the next generation with the various rich nutrients found in milk. Tons of milk powder produced by the European Union are shipped to Africa to save starving children there. But hunger has not been eliminated; instead, many children who enjoyed high-quality milk died from diarrhea. Most Africans cannot tolerate milk.
This inability to enjoy milk is scientifically known as "lactose intolerance." This phenomenon can be observed to varying degrees in many countries and ethnic groups. In Germany, Austria, and Switzerland, 12 to 18% of adults experience reactions such as abdominal pain, bloating, loose stools, or diarrhea from milk. This figure is 1% in Sweden, 50% in Italy, and nearly 100% in Thailand and China. No wonder, in many parts of Asia, milk is regarded as an unpalatable and unhealthy drink. How can such a surprising difference be explained?
When humans migrated from the equatorial regions to other areas, they had to adapt to less sunlight and colder climates. The synthesis of vitamin D in the skin requires the participation of light. Vitamin D, in turn, is a carrier of calcium. Without sufficient vitamin D, the body cannot get an adequate supply of calcium. The result is diseases such as childhood rickets, osteomalacia, and osteoporosis. If the skin does not get enough sunlight—whether because it is covered due to the cold or because of insufficient sunlight—there is a risk of developing the above diseases.
There are two solutions to this dilemma. For humans, the lower the pigment content in the skin, the more beneficial it is for absorbing more light in the process of synthesizing vitamin D. Therefore, people in the north have lighter skin. In addition, even after many people are weaned, their bodies maintain the ability to produce lactase. Because lactose also serves to transport calcium in the body, this can help offset the damage that insufficient sunlight might bring. For this, a milk supply is needed: this is the beginning of the dairy industry.
Those with "lactose intolerance" must not only be cautious with milk but also pay attention to dairy products. However, dairy products made with lactic acid bacteria, such as yogurt, contain very little lactose. This is because first, the lactose is already removed along with the whey, and second, those microbial enzymes also break down the lactose. Therefore, yogurt is more easily tolerated than milk. However, many current dairy products contain whey and milk powder that contain lactose. What is particularly troublesome for those with "lactose intolerance" is that lactose is now found in many current foods (such as instant soups, candies, and pastries) and in pharmaceutical preparations.