Lactose (milk sugar) requires lactase (an enzyme produced in the gut) in order to be digested. If there is little or no lactase activity in the intestines, the lactose ferments -- causing gas, bloating, abdominal pain, loose frothy stools, or diarrhea. Sometimes the gastrointestinal symptoms of a lactose intolerance are minimal and the person simply suffers from undue fatigue. And the nondigestibility of lactose by these people means that they lose some of the nutritional value of the milk.
Lactose intolerance accompanies diseases that damage the intestine, such as celiac disease, Crohn’s disease, and malabsorption syndrome -- and may also be a factor in many cases of colitis, irritable bowel, spastic colon and gastroenteritis.
On a worldwide basis, most adults are unable to digest lactose (milk sugar).
A small percentage of people are born with a lactose intolerance; however, its incidence increases significantly with age. That is because, genetically speaking, the human body was not designed to drink milk after the weaning period. In most cultures the world over, adults do not drink milk; they do not need the lactase enzyme; and their bodies stop producing it.
Blacks living in North America have been found to be from 72 to 77 per cent lactose intolerant. Chinese and Malays may be up to 100 per cent lactose intolerant. A high incidence of lactose intolerance has also been found among Colombians and Canadian native peoples, Jamaican children, Mexicans and Mexican Americans. A study of nonwhite children living in Boston revealed a lactose intolerance rate of 72 per cent among those eight to nine years of age. Other studies suggest the following approximate percentages of lactose intolerance: Bantu’s 90, This 90, Filipinos 90, Greek Cypriots 85, Japanese 85, Taiwanese 85, Greenland Intuit 80, Arabs 78, Ashkenazic Jews 78, Peruvians 70, Israeli Jews 58, Indians 50.
Some cultures who consume milk as a dietary staple have, over thousands of years, genetically adapted so that they can produce lactase throughout adult life. For example, the Fulani tribe of northern Nigeria (nomadic dairy herders) and the dairying tribes of Uganda have a substantially lower lactose intolerance rate of about 20 per cent. In Northern Europe, where dairying has been practiced for many centuries, the incidence of lactose intolerance is approximately 15 per cent. On the other hand, the Yorubo and Ibo tribes of Nigeria (who raise no cattle and drink no milk after weaning) become 99 per cent lactose intolerant between eighteen months and three years of age.
To simplify: Caucasian adults are about 15 per cent lactose intolerant, non-Caucasians from about 70 per cent to 90 per cent. people typically come from a variety of ethnic backgrounds. The 1991 census suggests that about 60 per cent are of European origin; the other 40 per cent are from Asian, African, Latin/Central/South American, Caribbean, aboriginal, other or multiple origin. When all of the genetic predisposition's are considered, it is very likely that over one third of all adult people may be lactose intolerant. That’s at least five million people.