Lactase is an enzyme produced in the small intestine. This protein helps the body process lactose, a sugar found in milk and various dairy products. Its presence allows individuals to break down milk sugars into simpler forms that the body can readily absorb for energy. Understanding lactase is foundational to comprehending how many people experience digestive responses to dairy consumption.
The Biological Role of Lactase
Lactase, also known as lactase-phlorizin hydrolase (LPH), is situated on the brush border of the small intestine, on the surface of cells called enterocytes. These cells line the intestinal walls, forming a barrier through which digested food nutrients must pass to be absorbed into the bloodstream. Lactase acts as a catalyst, speeding up a chemical reaction without being consumed.
The function of lactase involves breaking down lactose, a disaccharide. Lactase performs hydrolysis, a reaction where water is used to split lactose into its two constituent monosaccharides: glucose and galactose. Once broken down, these simpler sugars are absorbed by the small intestine and transported into the bloodstream for energy.
Lactase Nonpersistence and Deficiency
Humans are born with high levels of lactase activity, allowing infants to digest breast milk or formula. After weaning, lactase production naturally declines for most of the global population. This decrease in enzyme activity is known as lactase nonpersistence and is considered the normal state for approximately two-thirds of adults worldwide. Its prevalence varies significantly across different ethnic groups and regions; for instance, it affects 70% to 100% of people of East Asian descent, but only about 5% of those of Northern European descent.
Lactase deficiency can manifest in different forms. Primary lactase deficiency is the most common type, where enzyme activity gradually reduces after infancy due to genetic factors. Secondary lactase deficiency results from injury or illness affecting the small intestine, such as gastroenteritis, celiac disease, Crohn’s disease, or certain medications. This type is often temporary and can improve once the underlying condition resolves. A much rarer genetic disorder is congenital lactase deficiency, where infants are born with little to no lactase activity. This severe condition can lead to intractable diarrhea and faltering growth from the first exposure to lactose-containing milk.
When lactase levels are insufficient, undigested lactose passes from the small intestine into the large intestine. There, bacteria ferment the unabsorbed lactose, producing gases such as hydrogen, carbon dioxide, and methane. This fermentation also draws excess fluid into the bowel. The combined effect of gas production and fluid influx leads to digestive symptoms, including abdominal bloating, gas, stomach cramps, and diarrhea, typically appearing 30 minutes to two hours after consuming lactose-containing foods.
Managing Low Lactase Levels
Managing the effects of low lactase levels involves two strategies: dietary adjustments and enzyme supplements. Dietary management focuses on controlling the amount of lactose consumed to match an individual’s tolerance. Many people with reduced lactase can still tolerate small quantities of lactose, such as about a half cup of milk, or dairy products with naturally lower lactose content. Hard cheeses, like cheddar and Parmesan, and yogurts with live active cultures often contain less lactose, making them better tolerated.
Individuals can also choose lactose-free alternatives, which are widely available and contain the same nutrients as their regular counterparts, including calcium and vitamin D. These products have already had the lactase enzyme added during processing, breaking down the lactose before consumption. When reading food labels, look for ingredients like milk solids, skim milk powder, or whey, as these indicate lactose presence. Spreading lactose-containing foods throughout the day and consuming them with other foods can also slow digestion, allowing more time for any remaining lactase to act.
For those who wish to consume dairy products without strict dietary avoidance, over-the-counter lactase enzyme supplements offer a practical solution. These supplements contain the lactase enzyme, usually derived from yeasts or molds, and are designed to be taken with the first bite or sip of lactose-containing food. The added enzyme helps break down lactose in the digestive tract, preventing uncomfortable symptoms. Different brands offer various strengths, allowing individuals to choose a product that matches their level of intolerance and typical dairy intake.