In a nutshell
In some people, the enzyme lactase remains highly active in adulthood. This lactase persistence makes it easier to digest milk sugar and often results from genetic variants that affect gene activity.
Why does it happen?
Lactase sits on the surface of small-intestinal cells and breaks down milk sugar. In many people, its production declines after childhood. Regulatory variants can maintain activity of the LCT gene for longer; the frequency of these variants differs among populations.
Frequency
Lifelong high lactase activity differs greatly among populations and family ancestries. A single worldwide rate would obscure these differences.
Frequency is a qualitative description, not your individual probability.
Is it normal?
Lactase persistence and declining lactase activity are both normal human variations.
When to seek advice
Symptoms after milk do not prove a particular genotype; persistent pain, diarrhea, or weight loss should be assessed.
Does this happen to you?
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Sources (1)
- Evolution der Laktasepersistenz als Beispiel menschlicher Nischenkonstruktion (opens a new tab)
The review describes genetically influenced maintenance of lactase activity and its relationship to dairying.
Editorial update: . AI-assisted research and editing; not individually reviewed by a physician. How we research
