Lactose and your genes
How the LCT -13910 C>T variant (rs4988235) predicts whether you keep making lactase as an adult, what it can and cannot tell you, and how to eat dairy with low lactase.
The short answer
Most adults in the world make much less lactase than they did as children. In people of European ancestry, one DNA variant near the LCT gene, rs4988235 (also written -13910 C>T), tracks closely with whether lactase production continues. Two copies of the C version means lactase has very likely declined. The result predicts enzyme levels, not symptoms: plenty of people with low lactase handle modest amounts of dairy.
How common is low lactase?
A 2017 meta-analysis covering 89 countries estimated that 68% of adults worldwide have lactose malabsorption (95% CI 64–72). The figure swings widely by region, from about 28% in western, southern and northern Europe to about 70% in the Middle East.1 Keeping lactase into adulthood is the evolutionary exception, and it spread in populations with a long history of dairying.
The variant GenomEats reads
The variant sits about 14 kilobases upstream of the LCT gene, inside a neighbouring gene called MCM6, where it acts as a switch for lactase expression. Its discovery in Finnish families showed it was completely associated with biochemically verified lactase non-persistence in the people studied.2
| Your result at rs4988235 | What it usually means |
|---|---|
| CC | Lactase production has most likely dropped since childhood. |
| CT | Lactase usually persists. One copy of T is generally enough. |
| TT | Lactase usually persists. |
Where the result is weaker
Lactase persistence evolved more than once. In parts of East Africa and the Middle East, other variants close to -13910 do the same job, and a study of Ethiopian populations found several of them circulating together.3 If your ancestry is from those regions, a CC result at rs4988235 says less, because a consumer chip may not test the alternative variants. GenomEats flags this instead of reporting a confident answer.
What GenomEats suggests with a CC result
- Test your own tolerance rather than cutting dairy entirely. Small servings taken with a meal are often fine.
- Lean on lower-lactose dairy: lactose-free milk, aged hard cheeses, and yogurt or kefir with live cultures.
- If you cut back on milk, keep an eye on calcium and vitamin D from other foods.
- If dairy causes real trouble, or you have symptoms with no dairy involved, talk to a clinician. Other conditions can look like lactose intolerance.
Sources
- Storhaug CL, Fosse SK, Fadnes LT. Country, regional, and global estimates for lactose malabsorption in adults: a systematic review and meta-analysis. Lancet Gastroenterol Hepatol. 2017;2(10):738–746. pubmed.ncbi.nlm.nih.gov
- Enattah NS, Sahi T, Savilahti E, et al. Identification of a variant associated with adult-type hypolactasia. Nat Genet. 2002;30(2):233–237. pubmed.ncbi.nlm.nih.gov
- Jones BL, et al. Diversity of lactase persistence alleles in Ethiopia: signature of a soft selective sweep. Am J Hum Genet. 2013. pubmed.ncbi.nlm.nih.gov
This page is educational and does not diagnose or treat any condition. Talk to a qualified clinician before making medical decisions based on a genetic result.