Lactose

Understanding lactose intolerance

Lactose intolerance is a digestive condition affecting approximately 65% to 75% of the global population ^[1]. It occurs when the small intestine produces insufficient lactase, the enzyme needed to break down lactose—the sugar found in milk and dairy products—into glucose and galactose. Unlike a milk allergy, which triggers an immune response, lactose intolerance is a non-immunological digestive issue. The condition stems primarily from a natural decline in lactase production after weaning, a genetic trait that varies significantly across populations ^[2].

How lactose digestion works

When lactase is present in adequate amounts, it splits lactose molecules in the small intestine, allowing the resulting sugars to be absorbed into the bloodstream. Without sufficient lactase, undigested lactose travels to the colon where bacteria ferment it. This fermentation produces gas, causing bloating, flatulence, and abdominal cramps ^[2]. The osmotic effect of unabsorbed lactose also draws water into the intestinal lumen, potentially leading to diarrhea. Symptoms typically appear 30 minutes to 2 hours after consuming dairy and vary in severity from mild discomfort to significant digestive distress.

Genetic and ethnic patterns

Lactase persistence—the continued production of lactase into adulthood—is actually a relatively recent genetic adaptation linked to dairy farming in Northern European populations ^[1]. This explains why lactose intolerance rates vary dramatically by ancestry: approximately 90% of Northern Europeans maintain lactase production, while 70-100% of East Asian, African, and Indigenous populations experience some degree of intolerance. The MCM6 gene regulates lactase expression, and specific polymorphisms determine whether enzyme production continues into adulthood ^[1].

Secondary causes and triggers

Beyond genetic lactase decline, secondary lactose intolerance can develop following gastrointestinal infections, celiac disease, Crohn's disease, or other conditions that damage the intestinal lining ^[2]. This form may be temporary if the underlying cause resolves. Certain medications, particularly antibiotics and NSAIDs, can also reduce lactase activity by affecting the brush border where the enzyme is produced.

Dietary management and alternatives

Many lactose-intolerant individuals can tolerate small amounts of dairy, particularly fermented products like yogurt and aged cheeses, where bacteria have already broken down much of the lactose ^[2]. Hard cheeses such as cheddar and parmesan contain minimal lactose. Lactose-free milk and dairy products are widely available and provide the same nutritional benefits without the problematic sugar. For those avoiding dairy entirely, calcium can be obtained from fortified plant milks, leafy greens, sardines with bones, and tofu processed with calcium sulfate.

Lactase supplements

Over-the-counter lactase enzymes, taken with dairy-containing meals, can help many people digest lactose more comfortably ^[2]. These supplements provide the missing enzyme and are available in tablet or drop form. Effectiveness varies by individual and dose, so experimentation may be needed to find the right approach.