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Vitamin D: An Introduction 

Vitamin D plays a major role in maintaining bone health. It helps the body effectively utilize calcium from the diet. 

Some food sources of vitamin D include egg yolk, dairy, fatty fish, and grains. Exposure to sunlight is a major source of vitamin D. The UV rays in sunlight induce vitamin D production in the skin. About 15 minutes of exposure to sunlight is recommended to maintain optimal vitamin D levels. 

In today's world, people may not have enough exposure to sunlight.

Sunscreens are commonly used to prevent sunburns and tans, thereby blocking UV rays and the production of vitamin D. A sunscreen of SPF 30 can reduce the amount of vitamin D produced on sunlight exposure by more than 90%. 

Vitamin D Deficiency

The worldwide prevalence of vitamin D deficiency is very high, as high as 50%. Vitamin D deficiency leads to bone loss, pain, risk of fractures, and several disease conditions, like rickets and lupus. 

Certain groups of people are at an increased risk of vitamin D deficiency. These include: 

Vitamin D Supplements: Are They For You?

Very few foods have enough vitamin D to reach recommended daily intakes, and sunshine can be unreliable in certain climates. 

In these cases, vitamin D supplements can be taken in addition to food sources.

Make sure to talk to your doctor before taking vitamin D supplements.

Overdose can lead to vitamin D toxicity, which is dangerous. 

Melanin and Vitamin D 

Vitamin D production depends on several factors, including the color of your skin, duration of exposure, amount of skin exposed, and genetics. 

People with darker skin have more melanin, the pigment responsible for skin color. This protects skin cells from harmful radiation damage. 

Melanin also blocks the amount of UVB radiation that enters the skin, thereby reducing the amount of vitamin D produced. So people with darker skin tones are at a higher risk for vitamin D deficiency.

Genetics of Vitamin D Deficiency

Studies have found some genetic changes associated with vitamin D deficiency.

Two such genes are GC and VDR.

Let's see how they regulate vitamin D levels.

  1. The GC gene contains instructions for producing vitamin D binding protein that binds to the active form of vitamin D.
  2. Active vitamin D is then transported to target cells by this protein.
how much vitamin D should I take
  1. Active vitamin D is released at the target cell and can bind to the Vitamin D Receptor produced by the VDR gene.
  2. This complex then binds to several other proteins to influence gene expression and calcium homeostasis.
how much vitamin D should I take

This is especially seen in organs like the kidneys, bones, intestines, parathyroid glands, and the cardiovascular system. 

Mutations or changes in the VDR gene affect vitamin D levels and can increase or decrease the sensitivity of the body to the effects of vitamin D. 

Vitamin D Genetic Test

You can easily find out if you have any genetic variations that affect your vitamin D levels through a genetic test.

Most genetic tests provide your DNA information in the form of a text file, called the raw DNA data.

This data may seem like Greek and Latin to you. Xcode Life, can help you interpret it.

All you have to do is upload your raw data and order a nutrition report. Xcode Life then analyzes your raw data in detail to provide you with comprehensive nutrition analysis, including information on your vitamin D levels.


The sun has always been the most important source of energy for all living beings in the world. The sun makes life possible.

Your body needs sunlight to stay healthy. Sunlight is the major source of vitamin D for human beings. 

Vitamin D is a kind of fat-soluble vitamin needed by all living beings. This vitamin is also known as calciferol. Though it is present in a few food sources like fatty fish (salmon, tuna, sardines), mushrooms, and egg yolks, a majority of vitamin D is obtained from sunlight naturally. 

What are the significant functions of vitamin D?

Depending on their chemical composition, there are 5 different types of vitamin D available.

Out of these, Vitamin D2 and D3 are the major ones usually discussed. 

The Story Behind Vitamin D

Rickets is a condition that causes soft bones in children. The telltale signs of rickets are bowed legs, an abnormally large forehead, a curved spine, and stunted growth. 

There are mentions of children born with deformed bones as early as in the first and second centuries AD. Though rickets was not identified as a specific medical condition until 1645, instances of children born with bone deformities were quite common. 

Until the early 20th century, the reason and cure for rickets remained a mystery. Parents with newborns had no idea whether their child would grow up healthy or end up with bone deformities and stunted growth.

In 1914, Elmer McCollum, an American biochemist, identified that a certain additive in cod liver oil helped prevent rickets. He assumed it was vitamin A.

In 1922, he realized that cod liver oil without vitamin A, also prevented rickets. This led to the identification of a new 4th vitamin in history and this was named vitamin D. At that time, people did not realize sunlight could produce vitamin D.

That knowledge was brought forth by another American physician Alfred Hess who concluded “Light equals vitamin D”

Molecular Role Of Vitamin D- Getting Technical

The skin consists of two layers - the outermost layer, epidermis and the inner layer, dermis. The epidermis is made up of 5 layers. Vitamin D is produced using sunlight by the two innermost layers of the epidermis.

7-Dehydrocholesterol, also known as 7-DHC, is a chemical compound that is made in the skin in large quantities. 7-DHC reacts with the ultraviolet (UV) rays from the sun and is converted into vitamin D.

This process happens in the arms, legs, and face. The produced vitamin D is then carried in the blood to the liver. Here it is converted into a pre-hormone (a chemical substance produced by glands that is later converted into hormones) known as calcifediol. 

Calcifediol is then converted into calcitriol in the kidneys, which is the vitamin D form actually used by the body. From here, calcitriol is sent out for circulation. 

Did You Know?

More and more doctors and scientists globally are encouraging people to increase their vitamin D intake to prevent the severity of the COVID-19 infection.

With the vaccine for coronavirus still not approved or available, people are looking towards alternate solutions to boost their immunity. Vitamin D has emerged as a powerful nutrient to keep away infections.

There are a few notable studies conducted around the world that link vitamin D deficiency to an increased risk of developing COVID-19. Some studies say people living in areas that receive lesser amounts of sunlight see higher coronavirus deaths. 

Few other studies point to the fact that people with vitamin D deficiency seem to have worse symptoms when they test positive for the infection.

While there could be links between vitamin D consumption and the effects of the coronavirus, as of now, there is no solid proof that the vitamin can completely prevent or cure the infection.

The National Institutes of Health has also given out a statement stating that there is no evidence vitamin D can treat COVID-19.

However, making sure you get your recommended dose of vitamin D will definitely keep your immune system healthy during this pandemic.

Recommended Values

According to the Food and Nutrition Board, here are the daily recommended intake values of vitamin D.

What Happens When You Take Excess Of Vitamin D?

Excess quantities of vitamin D are unsafe. When you consume excess vitamin D, the calcium levels in the body increase too. This condition is called hypercalcemia. Hypercalcemia can result in the below conditions:

Vitamin D toxicity can also cause hypercalciuria (excess calcium in the urine). Extreme cases of vitamin D toxicity can lead to renal failure, irregular heartbeat, and even death.

Overexposure to the sun does not usually cause vitamin D toxicity because the skin learns to regulate the amount of vitamin D it produces. However, excessive use of tanning beds and excess consumption of vitamin D supplements can both cause vitamin D toxicity. 

What Happens When You Have Vitamin D Deficiency

When your vitamin D levels are low because of unhealthy eating habits and less/no exposure to sunlight, you can get vitamin D deficient with time. 

In children, vitamin D deficiency is reflected as rickets disease. Children can also suffer from developmental delays and dental problems early on. In adults, this can cause a condition called osteomalacia. Osteomalacia causes soft and weak bones. Adults also develop dental issues because of vitamin D deficiency. 

Non-genetic factors affecting Vitamin D levels

Genetic Association

There are two genes that seem to affect vitamin D concentrations in the body. Variations in these genes can cause increased/decreased needs for vitamin D.

GC gene - The GC gene is responsible for making the Vitamin D binding protein (VDBP) that helps in transporting vitamin D. One particular variant (type) of the GC gene is known to cause vitamin D deficiency.

CYP27B1 gene - The CYP27B1 gene is responsible for making vitamin D active and available for use by the cells in the body. One particular type of this gene can cause lowered vitamin D levels in the body.

Recommendations For Healthy Vitamin D Levels


  1. Vitamin D is a fat-soluble essential vitamin that is majorly got from sunlight. Vitamin D is also called calciferol. 
  2. There are five types of vitamin D found and D2 and D3 are the major ones. 
  3. Excess consumption of vitamin D is harmful and leads to hypercalcemia and hypercalciuria. Vitamin D deficiency leads to rickets in children and causes soft bones (osteomalacia) in adults
  4. Lesser exposure to sunlight and imbalanced food choices can all result in vitamin D deficiencies. 
  5. As people age, their vitamin D needs are not met sufficiently. People with health conditions like renal diseases or ulcerative colitis also are at risk of developing vitamin D deficiency.
  6. Genetically, you may be designed to require more vitamin D than regular recommended doses. In that case, you should compensate with fortified foods and supplements.


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?

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



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

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