Lactose is a sugar naturally present in milk and dairy products, such as cheese and butter. Lactase, on the other hand, is an enzyme instrumental in the digestion of milk. The human body produces both lactose and lactase; however, only women can produce lactose and it does not enter their bloodstream. Lactose is not necessary for nutrition. Alternately, it is present in milk as a source of immediate energy alongside fat, a long-term energy source.
Lactose
Lactose is a disaccharide comprised of glucose and galactose that naturally occurs in milk produced by mammals. It is the only sugar naturally present in animals, while all other sugars derive from plants. Lactose is a reducing sugar, which means that it donates rather than extracts electrons during chemical synthesis, reducing oxidization and the release of free radicals. However, this does not reduce other detriments associated with inordinate sugar consumption. It also means that warming produces a browning effect that alters taste. Mammals produce lactose in mammary glands via the Leloir pathway by first converting glucose molecules to galactose, then joining them each with one other glucose molecule. Lactose appears in mammalian milk as a source of energy in addition to other nutrients and fat.
Lactase
As part of digestion, the body absorbs a great deal of the nutrients that enter the body through the intestine. However, these nutrients often require processing before the intestines can absorb them. In the case of sugar, the intestine can only absorb monosaccharides, requiring that the digestive tract break down more complex sugars before they can be absorbed. To fulfill this requirement with lactose, lactase, an enzyme, is secreted through the small intestine. Lactaste then divides lactose into two absorbable glucose molecules.
Lactose Intolerance
The small intestine readily produces lactase in sufficient proportions in children. However, as humans age, they produce progressively less lactase until the amount released during lactose digestion becomes inadequate. At this point, lactose collects in the large intestine, absorbing water and intermingling with wastes. The result is cramps, gas and diarrhea, collectively known as lactose intolerance. This is correctable through lactase supplements and avoiding dairy products. As lactose is almost indistinguishably associated with milk, an intolerance to the sugar may be confused with a milk allergy. However, they are completely different.
Milk Allergy
A milk allergy, like all allergies, results from a malfunction in the immune system. Regarding milk specifically, the body recognizes some of the proteins present in the milk as a threat, resulting in an immunological response, which includes the release of antibodies, histamine and other chemicals. Risk factors of a milk allergy include the presence of other food allergies, a family history of food allergies--especially to milk--and atopic dermatitis. Moreover, the risk for developing an allergy to milk significantly increases with age. Symptoms of a milk allergy include hives, wheezing, diarrhea, vomiting, bloody stools, coughing, watery eyes, rash, runny nose and abdominal cramps. The best known treatment for a milk allergy is avoidance of milk altogether, according to MayoClinic.com.
References
- National Digestive Diseases Information Clearinghouse: Lactose Intolerance
- MedlinePlus.com: Lactose Intolerance
- MayoClinic.com: Milk allergy
- "Human Genetic Diversity: Functional Consequences for Health and Disease"; Julian C. Knight; 2009
- "Advanced Dairy Chemistry: Volume 3: Lactose, Water, Salts and Minor Constituents"; P. L. H. McSweeney and P. F. Fox; 2009
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