GC: your vitamin-D transport, decoded
You can get plenty of vitamin D and still test low, if the protein that ferries it around isn't pulling its weight.
Vitamin D doesn't float through your blood on its own. It rides on a carrier, the GC vitamin-D binding protein. A common variant at rs7041 makes that carrier a little less efficient. You transport and hold onto less vitamin D as a result, which is how you can run low even when your intake looks fine.
What GC does
The simple move: check your level with a 25(OH)D blood test. If it's low, top up with vitamin D3 and pair it with K2, which helps steer calcium where it belongs.
This variant nudges up your baseline risk of running low. Vitamin D does the same job in everyone, so nothing here is unique to your genotype. Your starting point just sits lower.
Your variants, decoded
The A allele is linked to weaker vitamin-D transport.
| AA | Two copies. The lowest transport of the three, and the genotype where checking your level pays off most. |
| AC | One copy. Transport runs a bit lower, so deficiency is more likely. |
| CC | Typical transport. |
We show genotypes on the forward strand and ignore letter order. Your own export may print the complementary letters. Same result either way.
What the research suggests
Your GC variant makes the vitamin-D binding protein a weaker carrier, so you tend to transport less and run lower. D3 supports healthy levels. The K2 alongside it helps direct calcium to the right places.
PubMed 29196501 · GC rs7041 (vitamin-D binding protein) & serum 25(OH)D
Educational only, not medical advice. “General evidence” means the finding is real, but the benefit isn’t specific to your genotype.
See this matched to your own DNA, free.
Upload your 23andMe or AncestryDNA file and you'll get your actual GC result, plus every other variant worth acting on. Every line cited. Your file is never stored.
Questions
Does the GC gene cause vitamin D deficiency?
Not on its own. It makes vitamin D harder to ferry around your blood, which tilts you toward running low. Your actual level still comes down to how much you take in and how much sun you get. A blood test settles it.