Lactase is an enzyme produced in the small intestine. It functions by breaking down lactose, a complex sugar found in milk, into simpler sugars: glucose and galactose. These simpler sugars are then absorbed by the body. The body regulates lactase production, ensuring its availability when needed.
The Role of Lactase and Lactose Intolerance
Lactase is found in the brush border of enterocytes lining the small intestine. Its job is to hydrolyze lactose into glucose and galactose, making them absorbable. Lactose is present in milk and dairy products.
When insufficient lactase is produced in the small intestine, lactose cannot be broken down and absorbed. This undigested lactose travels to the large intestine, where bacteria ferment it. This fermentation generates gases like hydrogen, carbon dioxide, and methane, which lead to symptoms of lactose intolerance. These symptoms include abdominal pain, bloating, excessive gas, nausea, and diarrhea, appearing 30 minutes to 2 hours after consuming lactose-containing foods.
The Genetic Switch for Lactase Production
The production of lactase is controlled by the LCT gene, located on chromosome 2. This gene provides the instructions for making the lactase enzyme. For the LCT gene to produce lactase, its promoter region requires a regulatory element called the MCM6 enhancer.
The MCM6 enhancer is not part of the LCT gene but is located upstream of it, within the MCM6 gene. This enhancer acts like a “switch,” influencing whether the LCT gene is turned on or off. In most mammals, and many humans, this genetic switch reduces lactase production after the weaning period, around 2 to 4 years of age. This decline in lactase activity is a normal biological process, leading to lactase non-persistence.
Lactase Persistence: A Human Adaptation
Lactase persistence is a human trait where individuals continue to produce lactase into adulthood. This ability is linked to genetic variations, known as single nucleotide polymorphisms (SNPs), located within the MCM6 enhancer region. These SNPs are changes in single DNA building blocks within this regulatory element.
For instance, the C/T-13910 SNP and G/A-22018 SNP are variants associated with lactase persistence, particularly in European populations. The presence of certain alleles, such as the T allele at position -13910, allows for lactase production. This adaptation is believed to have evolved recently, approximately 5,000 to 10,000 years ago, coinciding with the rise of dairy farming in certain populations. This phenomenon represents a variation in the regulation of the LCT gene, rather than a difference in the gene itself.
Understanding Your Body’s Lactase Activity
Diagnosing lactose intolerance often begins with a review of symptoms and a temporary reduction of dairy in the diet. Medical tests can confirm the diagnosis, with the hydrogen breath test being a common method. In this test, individuals consume a lactose-containing liquid, and the amount of hydrogen in their breath is measured at intervals; elevated hydrogen levels suggest improper lactose digestion. Another diagnostic tool is the lactose tolerance test, which measures blood glucose levels after lactose consumption. If glucose levels do not rise, it indicates poor lactose absorption.
Managing lactose intolerance primarily involves dietary adjustments. Individuals can limit or avoid foods high in lactose, opt for lactose-free dairy products, or consume smaller servings of dairy with meals. Over-the-counter lactase enzyme supplements can also be taken before consuming dairy to aid in lactose digestion. Understanding your body’s lactase activity empowers individuals to make informed dietary choices and manage their digestion.