GC: your vitamin-D transport, decoded
You can get plenty of vitamin D and still test low, if the protein that carries it around isn't pulling its weight.
Vitamin D doesn't float through your blood on its own. It hitches a ride on a carrier called the GC vitamin-D binding protein. A common variant at rs7041 makes that carrier a little less efficient, so you transport and hold onto less vitamin D, and you can run low even when your intake looks fine.
What GC does
The simple move is to get your level checked with a 25(OH)D blood test, and if it's low, top up with vitamin D3. Pair it with K2, which helps steer calcium where it belongs.
This variant nudges your baseline risk of running low. The vitamin D itself does the same job for 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. 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. |
Genotypes are shown order-insensitively and on the forward strand; your own export may print the complementary letters — the meaning is the same.
What the research suggests
Your GC variant makes the vitamin-D binding protein a less efficient carrier, so you tend to transport less and run lower. D3 supports healthy levels, and the K2 alongside it helps direct calcium to the right places.
Educational only — not medical advice. “General evidence” means the finding is real but the supplement’s benefit isn’t unique to your genotype.
See this matched to your own DNA — free.
Upload your 23andMe or AncestryDNA file and get your actual GC result, plus every other actionable variant — each line cited, your file never stored.
Questions
Does the GC gene cause vitamin D deficiency?
Not on its own. It makes vitamin D harder to transport in your blood, which tilts you toward running low, but your actual level still depends on how much you take in and how much sun you get. A blood test settles it.