Lactase is a digestive enzyme produced by cells that line the small intestine. It is embedded within the cell membranes of these cells, with its active parts extending into the intestine where digestion occurs. Its primary role is to break down lactose, the sugar found in milk and dairy products.
The Function of Lactase
Lactose is a large sugar, known as a disaccharide, which is too large to be absorbed directly through the intestinal wall. Lactase acts as a catalyst that splits lactose into two smaller sugars: glucose and galactose. These are then absorbed by the intestinal cells and transported into the bloodstream, where they are used for energy.
Lactase is most active during infancy when milk is the primary source of nutrition. For many people, its production naturally declines after the weaning phase.
Lactase Deficiency and Its Consequences
When the small intestine does not produce enough lactase, a person has lactase deficiency, which leads to lactose intolerance. This condition causes digestive symptoms after consuming dairy because undigested lactose passes into the large intestine, or colon. In the colon, gut bacteria ferment the lactose, producing gases like hydrogen, carbon dioxide, and methane, which leads to bloating and flatulence. The unabsorbed sugar also draws water into the bowel, resulting in diarrhea and abdominal cramps. Symptoms typically begin 30 minutes to two hours after consuming lactose-containing foods.
The most common cause is primary lactase non-persistence, a genetically determined decline in lactase production with age. Production is highest at birth and typically begins to decrease around age three, though symptoms may not appear until adulthood. Less common is secondary lactase deficiency, which can result from an injury to the small intestine from illness or certain medical conditions.
Managing Lactase Deficiency
One common approach to managing symptoms is using over-the-counter lactase supplements. Available as tablets or drops, these supplements provide the enzyme needed to break down lactose and are taken just before consuming dairy. Another method is consuming lactose-free or lactose-reduced dairy products. During manufacturing, lactase is added to these products to pre-digest the lactose.
Many people find they can tolerate small amounts of lactose, especially when consumed with other foods. Gradually reintroducing dairy into the diet can help determine a personal tolerance level. Experimenting with different dairy products is also useful, as some, like hard cheeses and yogurt with live cultures, contain less lactose and may be better tolerated.