GC
Vitamin D-binding protein, originally known as GC is a protein that is encoded by the GC gene. Expressed in the liver and secreted into the blood GC is responsible for binding with the bioactive form of vitamin D, calcitriol and shuttling it through the circulatory system, into tissue and then presenting it to the vitamin D receptor (VDR) to allow its binding. This binding induces the uptake of calcium from the guy required for a wide range of activities including bone formation and muscle activity 1.
There is one SNP within GC which has been associated with reduced levels of vitamin D, A26-796C.
| rsID Number | Major Allele | Minor Allele | Minor Allele Frequency (%) |
|---|---|---|---|
| rs2282679 | t | c | 20 |
Risk Description
The ‘C’ allele of SNP A26-796C is associated with a 10% reduction in the amount of vitamin D detected in the blood, in those with two ‘C’ alleles this is reduced by 20%. In those with two ‘C’ alleles the reduction in vitamin D pushed them into the “Vitamin D insufficiency” category, where dietary supplementation or longer sun exposure may be recommended. In those with the ‘C’ allele reduced amounts of GC were detected in the blood, which is thought to limit the amount of vitamin D present 2.
A lack of vitamin D is typically associated with boor bone health. In children, this can manifest as the disease rickets whereby bones are softened and weakened leading to poor development. This disease has been all but eradicated in the west due to fortification of key food groups, although some may still be at risk. Adults deficient in vitamin D are at risk of developing osteomalacia, where bones are thinned, and osteoporosis where bones become more fragile 3.
Although the ‘C’ allele of A26-796C is associated with a significant reduction in circulating vitamin D levels, no impact on bone health or fracture risk has been described 4.
However, outside of bone health a lack of vitamin D, associated with the ‘C’ allele of A26-796C has been associated with several cancers including liver, pancreatic and ovarian 5.
Direct Nutrients:*
| Ingredient | Active Ingredient | Effect |
|---|---|---|
| Vitamin D | Calcitriol |
GC is responsible for transporting the bioactive form of vitamin D throughout the circulatory system and into tissues where it is required. In those with the ‘C’ allele of SNP A26-796C, where levels of circulating vitamin D are reduced supplementation with the bioactive form of vitamin D, calcitriol, may help ensure that appropriate vitamin D levels are maintained ensuring proper calcium uptake maintain bone health and ensuring normal cellular function. Additionally, given that the majority of us are vitamin D deficient anyway supplementation is to be recommended to ensure both healthy calcium uptake, and that the other cellular activates dependent on vitamin D can proceed normally 6. |
Indirect Nutrients:*
| Ingredient | Active Ingredient | Effect |
|---|---|---|
| Calcium |
The major function of vitamin D binding to VDR is to promote proper uptake of calcium from the gut. Whilst, calcium is not typically limited in a normal diet those pursuing a vegan, or dairy free diet may consider supplementation, especially if they carry the risk ‘C’ allele of A26-796C in the GC gene 7. |
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Discuss this information with your doctor before taking any course of action.
Citations:
- https://www.ncbi.nlm.nih.gov/pubmed/3190085
- http://dx.doi.org/10.1016/S0140-6736(10)60588-0
- https://www.ncbi.nlm.nih.gov/pubmed/22613962
- https://www.ncbi.nlm.nih.gov/pubmed/23734184
- https://www.ncbi.nlm.nih.gov/pubmed/25799011
- https://www.ncbi.nlm.nih.gov/pubmed/27594614
- http://dx.doi.org/10.1016/S0140-6736(10)60588-0
- http://www.nhs.uk/Livewell/Vegetarianhealth/Pages/Vegandiets.aspx