Lactase is a digestive enzyme that breaks down lactose, the primary sugar found in milk and dairy products. This enzyme acts as a catalyst, preparing lactose for absorption into the bloodstream so the body can utilize the sugar for energy. Without sufficient lactase activity, the body cannot properly process dairy sugars, which often results in digestive distress.
The Role of Lactase in Digestion
Lactase is produced by cells lining the small intestine, specifically on the brush border membrane. This location is where the final stages of carbohydrate digestion occur before nutrient absorption begins. The enzyme hydrolyzes lactose, which is classified as a disaccharide, by splitting the molecule into its two constituent monosaccharides: glucose and galactose.
These smaller, individual sugar molecules are then easily absorbed through the intestinal wall into the bloodstream. Successful digestion prevents the lactose from traveling further down the digestive tract where it would otherwise cause problems. Lactase activity is naturally highest during infancy when milk is the sole source of nutrition, and it typically begins to decline after the weaning period.
Understanding Lactase Deficiency
A deficiency in lactase production means the small intestine does not create enough of the enzyme to process the lactose consumed. The most common form is primary lactase deficiency, also known as lactase non-persistence, which is genetically predetermined. This is an age-related decline in enzyme activity that occurs gradually after early childhood.
Secondary lactase deficiency results from damage to the small intestine’s lining. Conditions such as celiac disease, Crohn’s disease, or acute intestinal infections can injure the enterocytes, the cells responsible for lactase production. Unlike the primary form, this deficiency is often temporary and can improve or resolve once the underlying disease or injury is successfully treated. In rare cases, an infant may be born with congenital lactase deficiency, an inherited condition where the enzyme is absent from birth.
Symptoms and Management of Lactose Intolerance
When lactase is deficient, undigested lactose moves out of the small intestine and into the colon. There, the sugar encounters the native gut bacteria, which begin to ferment the lactose. This process of fermentation releases gases, including hydrogen, carbon dioxide, and methane, which are the direct cause of many uncomfortable symptoms.
Common physical manifestations of this bacterial activity include abdominal bloating, cramping, and excessive flatulence. The presence of undigested sugar in the colon also draws water into the intestine, which often results in diarrhea. These symptoms typically begin to appear between 30 minutes and two hours after consuming a food or drink that contains lactose. The severity of the reaction depends on the degree of lactase deficiency and the total amount of lactose ingested.
Management of lactose intolerance focuses on reducing the amount of undigested lactose entering the colon. Complete elimination of dairy is rarely necessary, as most individuals can tolerate a certain threshold of lactose, often up to 12 grams per sitting. Dietary adjustments involve choosing products that naturally contain less lactose, such as hard cheeses and yogurt, which have had much of the sugar processed out by their own bacterial cultures.
Another highly effective strategy is the use of exogenous lactase enzyme supplements. These are available in tablet or drop form and are consumed immediately before eating dairy products. The supplement provides the missing enzyme in the digestive tract, allowing the lactose to be broken down before it reaches the large intestine. Many people also find relief by selecting commercially available lactose-free milks and products, which have already been treated with the lactase enzyme.