Humans are the only mammals that continue to drink milk after they finish breastfeeding as babies. However, around 60 percent of all people are estimated to develop lactose intolerance, which is the inability to digest dairy products, according to a Cornell University News Service. Since a lack of dairy can lead to nutritional deficiencies, check with your doctor to make sure you are lactose intolerant before avoiding dairy.
If you have gas, bloating, cramps or diarrhea after eating dairy products, lactose intolerance could be the cause. People with lactose intolerance do not make enough lactase, an intestinal enzyme that breaks down the lactose sugar in milk. There are different ranges of intensity of lactose intolerance, so some people cannot tolerate any dairy while others can have up to 12 oz. with no symptoms.
It is normal for people to make less lactase as they age, but certain races generate more lactase than others. According to a May 2002 article in the "American Family Physician," some ethnic groups have high levels of lactose intolerance including up to 100 percent of Asians and Native Americans, 60 to 80 percent of blacks and 50 to 80 percent of Latinos. Conversely, only up to 15 percent of those with northern European ancestry have symptoms of lactose intolerance.
It is unclear whether the populations who can better tolerate dairy can do so because their bodies adapted to the consumption of dairy or because their bodies kept making lactase regardless of diet. Researchers from Cornell University surmise that lactose intolerance is related to groups' adaptation to their environments. A Cornell study concluded that ethnic groups with ancestors from climates supporting the production of dairy cattle, like Europe, can digest milk better than those with ancestors from places that did not have the right conditions for dairy cattle. These places include Asia and Africa.
It is difficult to determine the number of people with lactose intolerance, so the February 2010 NIH Consensus Development Conference on Lactose Intolerance and Health noted that some lactose intolerance statistics might be skewed. The conference explained that many studies on the subject have used self-reporting. This is a problem because the symptoms of lactose intolerance can also be caused by other conditions like irritable bowel syndrome, ulcerative colitis or celiac disease. Further, not everyone in certain ethnicities or races expected to have lactose intolerance experience the symptoms.
- Cornell University News Service; Lactose Intolerance Seems Linked to Ancestral Struggles with Harsh Climate and Cattle Diseases, Cornell Study Finds; Susan S. Lang; Jun. 1, 2005
- “American Family Physician”; Lactose Intolerance; Daniel L. Swagerty, Jr.; May 2002
- NIH Consensus Development Conference: Lactose Intolerance and Health; National Institutes of Health; Final Panel Statement; Feb. 22 to 24, 2010