The Group Specific Component globulin (GC) gene is associated with the synthesis of Group Specific Component globulin (GC), also called the Vitamin D Binding Protein (VDBP), which binds to vitamin D and its plasma metabolites, transporting them to the target tissue. This protein is synthesized by the hepatic parenchymal cells and then secreted into the blood stream. People with the C variant of the gene are shown to be associated with lower vitamin D levels.

Vitamin D is necessary for strong bones and for the absorption of calcium, low level of vitamin D is associated with brittle bones and poor muscle function. Vitamin D deficiency is identified by measuring the level of 25, hydroxy vitamin D in the blood. Increased plasma concentration of plasma 25, hydroxy vitamin D is associated with reduced risk of hypertension.

Does your 23andme, Ancestry DNA, FTDNA raw data have GC gene variant information?

CHIP VersionGC SNPs
23andMe (Use your 23andme raw data to know your GC Variant)
v1 23andmePresent
v2 23andmePresent
v3 23andmePresent
v4 23andmePresent
V5 23andme (current chip)Present
AncestryDNA  (Use your ancestry DNA raw data to know your GC Variant)
v1 ancestry DNAPresent
V2 ancestry DNA (current chip)Present
Family Tree DNA  (Use your FTDNA raw data to know your GC Variant)
OmniExpress microarray chipPresent

Association of Vitamin D concentration and ethnicity:

The GC gene is found to be the strongest genetic determinant of the bioavailability of 25, hydroxy vitamin D. There are three isoforms of GC- GC1F, GC2 and GC1S, they are based on a combination of alleles of the SNPs rs7041 and rs 4588 (rs 2282679 is a close proxy). The isoform GC1F is more common among people with dark skin when compared with people with pale skin. GC2 and GC1S are more common among people with pale skin than among people with dark skin.

The vitamin D binding protein (VDBP) in people with the GC1 isoform has a higher affinity for vitamin D metabolites. This is shown to be associated with variations in the bioavailability of circulating 25, hydroxy vitamin D levels among ethnicities.

Genotype Phenotype
CC[Limitation] More likely to have lower plasma 25, hydroxy vitamin D
CAModerate plasma 25, hydroxy vitamin D
AA[Advantage] More likely to have higher plasma 25, hydroxy vitamin D

How can this information be used?

It is important to choose an appropriate diet based on the genetic profile

For people with C variant (Decrease in plasma 25, hydroxy vitamin D) Likely decrease in plasma 25, hydroxy vitamin D Include 1000 I.U of vitamin D per day Ensure sufficient exposure to sunlight; include enjoyable activities like taking the dog for a walk or a day at the beach with family.
For people with A variant (Normal plasma 25, hydroxy vitamin D) Increased likelihood for normal level of plasma 25, hydroxy vitamin D if the dietary intake is sufficient Spend time outdoors for adequate exposure to sunlight

References:

  1. http://www.sciencedirect.com/science/article/pii/S2213858714701135
  2. https://hyper.ahajournals.org/content/49/5/1063.short
  3. https://www.ncbi.nlm.nih.gov/pubmed/26383826
  4. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3613945/
  5. https://www.ncbi.nlm.nih.gov/pubmed/26275945
  6. https://www.ncbi.nlm.nih.gov/pubmed/21972121?dopt=Abstract
  7. http://thelancet.com/journals/landia/article/PIIS2213-8587(14)70113-5/abstract
  8. http://hyper.ahajournals.org/content/49/5/1063.short

Nutrigenetics, fitness genetics, health genetics are all nascent but rapidly growing areas within human genetics. The information provided herein is based on preliminary scientific studies and it is to be read and understood in that context.”

Vitamin D and health

Vitamin D is a hot topic these days. We get it from the sun, fortified milk, butter, ghee, soybeans, soy milk, cheese, eggs and certain types of fish and mushrooms. It’s usually credited with promoting bone strength and overall health. And vitamin D deficiency has been linked to many chronic diseases, including, but not limited to, infectious diseases, autoimmune diseases, cardiovascular diseases, diabetes and cancer.

A recent study revealed that a whopping 70% of the Indians suffer from vitamin D deficiency. This study further adds that sunlight exposure is not a tenable solution to obtain vitamin D sufficiency among Indians, as darker skin has high melanin content and produces a significantly lesser amount of vitamin D when compared with individuals with fairer skin. Indian skin tone requires daily sunlight exposure of at least 45 minutes to produce sufficient amounts of vitamin D.

Vitamin D and genes

You may also need more vitamin D depending on the genes that you carry. Variations in two genes, GC and VDR, are responsible for lower vitamin D levels. The GC gene produces the main transporter of vitamin D in circulation while VDR  gene produces vitamin D receptor which allows the body to respond appropriately to vitamin D. Compared to others, people carrying one type of GC and one type of  VDR  need to ensure they have adequate sun exposure or dietary intake of vitamin D to avoid deficiency.

Diet and vitamin D

Various nutritional factors attributing to high prevalence of vitamin D deficiency in India are:

Most Indians are vegetarians and most of the foods rich in vitamin D are of animal origin. Indian diets are low in calcium and high in phytate. High prevalence of lactose intolerance is a major factor for reduced intake of calcium and vitamin D. Intake of caffeine from coffee and tea is high in India.

Factors such as age (old age), body weight (people with a body mass index of 30 or greater), problems of the digestive tract like Crohn’s disease and cystic fibrosis, kidney problems results in low blood levels of vitamin D.

The National Institute of Nutrition recommends 200 units, 5 mcg of vitamin D everyday. The following are the recommendations from the vitamin D council:

It is essential to maintain healthy levels by including fatty fish such as salmon, mackerel, herring, tuna, fish oils, egg yolks, fortified milk and other fortified foods such as cereals etc. Vitamin D supplements could be a good alternative. Many forms of vitamin D exist, with vitamin D3 the most effectively used in the body. Get adequate sunlight exposure: The amount of vitamin D you get from exposing your bare skin to the sun depends on the time of the day, where you live, the color of your skin and the amount of skin you expose.

Want to know what type of VDR and GC gene you have, Xcode’s nutrigenetics test can tell you what versions of the VDR & GC gene you have in your DNA. You can also learn about how your genes may influence other traits, including your risk for certain diseases.  You can write to us at hello@xcode.life.

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