What you carry at this position in your DNA and what research says about it.
Vitamin D Levels: 10/10 evidence, 52 publications.
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Sample genotype (not yours): G/G
Optimal Vitamin D Levels and Lower Deficiency Risk
Optimal vitamin D transport and higher circulating levels characterize this genetic profile. It provides natural protection against deficiency under typical sun exposure and dietary conditions.
What this genotype means: Higher circulating vitamin D levels; Lower risk of vitamin D deficiency; Efficient vitamin D transport.
Sample genotype (not yours): G/T
Typical Vitamin D Levels with Moderate Deficiency Risk
Intermediate levels of vitamin D and its binding protein are typical for this genetic profile. It represents a standard baseline, though seasonal sun exposure and diet remain key to maintaining sufficiency.
What this genotype means: Intermediate vitamin D levels; Moderate susceptibility to seasonal vitamin D drops.
Sample genotype (not yours): T/T
Lower Vitamin D Levels and Higher Deficiency Risk
Lower circulating levels of vitamin D and its transport protein are common with this genetic profile. It significantly increases the likelihood of experiencing vitamin D deficiency, especially without supplementation.
What this genotype means: Significantly lower circulating vitamin D; Increased risk of vitamin D deficiency; Altered response to specific cancer therapies.
Gene function and biological role
Gene Function: The GC gene encodes the vitamin D-binding protein, a specialized globulin responsible for transporting vitamin D and its metabolites through the bloodstream to target tissues [1]. Beyond its primary role as a carrier, this protein acts as an actin scavenger, clearing cellular debris from circulation after tissue injury [2]. It also plays a crucial role in immune system regulation by facilitating macrophage activation and chemotaxis [2]. Variations in this gene directly influence how efficiently vitamin D is transported, stored, and utilized by the body [1].
Variant Impact: A missense mutation in exon 11 of the GC gene changes the amino acid at position 436 from threonine to lysine. This structural alteration directly impacts the vitamin D-binding protein's affinity for vitamin D metabolites and its overall concentration in circulation [2]. The threonine-encoding G allele is associated with higher protein levels and more efficient transport of vitamin D [1]. Conversely, the lysine-encoding T allele reduces both the concentration of the binding protein and the levels of circulating vitamin D [2]. This single-nucleotide change is one of the most significant genetic determinants of baseline vitamin D status in human populations [1].
Key Insight: This variant alters the actual structure of your vitamin D transport protein, not just how much of it is made.
Location: GC. Chromosome 4 · 4q13.3 · 71.8 Mb
Estimated prevalence by population
Global 61.0%; European 50.7%; African 80.4%; East Asian 55.3%; South Asian 50.7%; Americas 60.5%; Ashkenazi 50.7%; Finnish 64.4%; Middle Eastern 67.2%; Amish 34.7%.
Estimated GG genotype frequency.
Global 33.4%; European 41.0%; African 18.5%; East Asian 38.1%; South Asian 41.0%; Americas 34.6%; Ashkenazi 41.0%; Finnish 31.7%; Middle Eastern 29.6%; Amish 48.4%.
Estimated GT genotype frequency.
Global 5.6%; European 8.3%; African 1.1%; East Asian 6.6%; South Asian 8.3%; Americas 4.9%; Ashkenazi 8.3%; Finnish 3.9%; Middle Eastern 3.3%; Amish 16.9%.
Estimated TT genotype frequency.
Showing effects for G/G genotype
Nutrition & Metabolism
Vitamin & Mineral Metabolism
Vitamin D Levels. Evidence: 10/10. Source: PMID 29545823. Higher Levels.
Vitamin D Deficiency. Evidence: 10/10. Source: PMID 39024449. Lower Risk.
Vitamin D-Binding Protein. Evidence: 10/10. Source: PMID 34014961. Higher Levels.
Cardiovascular & Metabolic
Blood Cell & Iron Traits
Platelet Count. Evidence: 7/10. Source: PMID 32888494. Slightly Higher.
Pharmacogenomics
Chemotherapy Response
Cancer Drug Response. Evidence: 5/10. Source: PMID 29208668. Typical Response.
Showing effects for G/T genotype
Vitamin D Levels. Evidence: 10/10. Source: PMID 29545823. Typical Levels.
Vitamin D Deficiency. Evidence: 10/10. Source: PMID 39024449. Typical Risk.
Vitamin D-Binding Protein. Evidence: 10/10. Source: PMID 34014961. Typical Levels.
Platelet Count. Evidence: 7/10. Source: PMID 32888494. Typical.
Showing effects for T/T genotype
Vitamin D Levels. Evidence: 10/10. Source: PMID 29545823. Lower Levels.
Vitamin D Deficiency. Evidence: 10/10. Source: PMID 39024449. Increased Risk.
Vitamin D-Binding Protein. Evidence: 10/10. Source: PMID 34014961. Lower Levels.
Platelet Count. Evidence: 7/10. Source: PMID 32888494. Slightly Lower.
Cancer Drug Response. Evidence: 5/10. Source: PMID 29208668. Altered Response.
What this genotype means for the people who carry it
Sample genotype: GG (Homozygous)
Inheriting the G allele from both parents ensures the production of the threonine-encoding form of the vitamin D-binding protein, which has a higher affinity for vitamin D metabolites [1]. Large-scale genomic studies show that this genetic profile correlates with the highest baseline levels of circulating 25-hydroxyvitamin D [2]. Consequently, there is a significantly lower risk of developing vitamin D deficiency [3]. The efficient transport system also supports bone mineral density and overall calcium homeostasis [4]. While maintaining healthy levels is easier, adequate dietary intake and sun exposure remain important for overall health.
Higher circulating vitamin D levels; Lower risk of vitamin D deficiency; Efficient vitamin D transport.
Sample genotype: GT (Heterozygous)
A combination of one G allele and one T allele leads to the production of both the threonine and lysine variants of the vitamin D-binding protein. This hybrid profile typically results in intermediate circulating levels of 25-hydroxyvitamin D [1]. While not as highly protected as the homozygous major genotype, maintaining adequate vitamin D status is generally straightforward under normal conditions [2]. However, susceptibility to seasonal drops in vitamin D during winter months or with low dietary intake may be slightly higher [3]. Monitoring dietary intake of vitamin D and ensuring sensible sun exposure can help maintain optimal levels.
Intermediate vitamin D levels; Moderate susceptibility to seasonal vitamin D drops.
Sample genotype: TT (Homozygous)
Producing only the lysine-encoding variant of the vitamin D-binding protein leads to a lower overall concentration of the transport protein in the blood [1]. Multiple genome-wide association studies have confirmed that this genotype is associated with the lowest baseline levels of circulating 25-hydroxyvitamin D [2]. This reduction significantly elevates the risk of clinical vitamin D deficiency [3]. Additionally, this genetic profile may influence how the body responds to certain cancer therapies, such as showing altered survival outcomes with bevacizumab or cetuximab treatments [4]. Ensuring adequate vitamin D intake through diet or supplementation is often particularly important for individuals with this genetic background.
Significantly lower circulating vitamin D; Increased risk of vitamin D deficiency; Altered response to specific cancer therapies.
Variants with shared genetic architecture
rs2282679 · GC Gene · Chr 4 · Vitamin D Levels
rs7041 · GC Gene · Chr 4 · Vitamin D Levels
rs705117 · GC Gene · Chr 4 · Vitamin D Levels
Genome-Wide Association Study of Serum 25-Hydroxyvitamin D in US Women.
Diversity and scale: Genetic architecture of 2068 traits in the VA Million Veteran Program.
Content updated August 2026.
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