Lactose, calcium and the LCT gene

Most mammals, and most adult humans worldwide, stop digesting milk sugar after childhood. The ability to keep digesting it is a relatively recent genetic adaptation, and whether you have it changes more than your comfort after a latte.

Lactase usually switches off after childhood

Lactose, the sugar in milk, is broken down by the enzyme lactase. In the default human program, lactase production declines after weaning, which is why so many adults are lactose-intolerant. That decline is the norm, not a disorder.

LCT decides if yours stays on

The LCT gene region, through the variant rs4988235, determines “lactase persistence” — whether your lactase stays active into adulthood. Persistence carriers digest dairy comfortably; non-carriers experience the familiar symptoms when they do not.

The calcium catch

Here is the part that is easy to miss: lactose-intolerant people who simply cut out dairy often end up short of calcium, because dairy is a major dietary source. Avoiding the discomfort can quietly create a bone-health gap.

What actually helps

Non-persistence carriers can use lactase enzyme supplements, lactose-free dairy, or build calcium from non-dairy sources (leafy greens, fortified plant milks, certain fish) or supplements. The gene result turns “dairy upsets me” into a concrete nutrition plan.

The science, in depth

rs4988235 (-13910C>T), upstream of the LCT gene, is the principal European lactase-persistence allele, maintaining lactase-phlorizin hydrolase expression into adulthood. Non-persistence genotypes underlie adult lactose malabsorption and the associated risk of reduced calcium intake when dairy is avoided.