What you carry at this position in your DNA and what research says about it.
Vitamin D Levels: 10/10 evidence, 40 publications.
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Sample genotype (not yours): T/T
Typical Vitamin D Levels
This genotype is associated with optimal transport of vitamin D and a lower risk of deficiency. It supports healthy bone density and typical immune cell counts.
What this genotype means: Efficient vitamin D transport; Lower risk of deficiency; Typical immune cell counts.
Sample genotype (not yours): G/G
Lower Vitamin D and Higher Deficiency Risk
Carrying two copies of the G allele is strongly linked to lower circulating vitamin D levels. This genotype significantly increases the risk of vitamin D deficiency.
What this genotype means: Reduced vitamin D transport efficiency; Elevated risk of vitamin D deficiency; Lower baseline white blood cell counts.
Sample genotype (not yours): T/G
Somewhat Lower Vitamin D
Carrying one copy of the G allele is linked to slightly reduced vitamin D transport efficiency. This can result in moderately lower circulating vitamin D levels.
What this genotype means: Moderately reduced vitamin D transport; Slightly higher risk of deficiency; Slightly lower immune cell counts.
Gene function and biological role
Gene Function: The GC gene encodes the vitamin D-binding protein, which is the primary carrier of vitamin D in the bloodstream [1]. This protein binds to vitamin D metabolites and transports them to various tissues throughout the body [2]. By regulating the availability and distribution of circulating vitamin D, the gene plays a fundamental role in bone mineralization and calcium absorption [1]. It also influences immune system function, as many immune cells rely on vitamin D to coordinate inflammatory responses [3].
Variant Impact: This variant is an intronic change located within the GC gene that significantly influences how much vitamin D-binding protein is produced [1]. Because it alters the expression of this transport protein, the genetic change directly impacts the concentration of active vitamin D circulating in the blood [2]. The G allele is strongly associated with reduced transport efficiency and lower overall vitamin D levels [4]. Conversely, the T allele supports typical protein production and helps maintain stable, higher circulating levels of the vitamin [1].
Key Insight: This genetic variant is one of the strongest known genetic predictors of circulating vitamin D levels in the human genome.
Location: GC. Chromosome 4 · 4q13.3 · 71.7 Mb
Estimated prevalence by population
Global 62.0%; European 50.9%; African 83.2%; East Asian 55.3%; South Asian 51.0%; Americas 60.5%; Ashkenazi 50.7%; Finnish 66.3%; Middle Eastern 67.7%; Amish 34.9%.
Estimated TT genotype frequency.
Global 32.6%; European 40.9%; African 16.0%; East Asian 38.1%; South Asian 40.9%; Americas 34.5%; Ashkenazi 41.0%; Finnish 30.3%; Middle Eastern 29.1%; Amish 48.4%.
Estimated TG genotype frequency.
Global 5.5%; European 8.2%; African 0.8%; East Asian 6.6%; South Asian 8.2%; Americas 4.9%; Ashkenazi 8.3%; Finnish 3.5%; Middle Eastern 3.1%; Amish 16.8%.
Estimated GG genotype frequency.
Showing effects for T/T genotype
Nutrition & Metabolism
Vitamin & Mineral Metabolism
Vitamin D Levels. Evidence: 10/10. Source: PMID 20418485. Typical Levels.
Vitamin D Deficiency. Evidence: 10/10. Source: PMID 20541252. Typical Risk.
Cardiovascular & Metabolic
Blood Cell & Iron Traits
White Blood Cell Count. Evidence: 6/10. Source: PMID 32888494. Typical Count.
Neutrophil Count. Evidence: 8/10. Source: PMID 32888494. Typical Count.
Showing effects for G/G genotype
Vitamin D Levels. Evidence: 10/10. Source: PMID 20418485. Lower Levels.
Vitamin D Deficiency. Evidence: 10/10. Source: PMID 20541252. Higher Risk.
White Blood Cell Count. Evidence: 6/10. Source: PMID 32888494. Lower Count.
Neutrophil Count. Evidence: 8/10. Source: PMID 32888494. Lower Count.
Showing effects for T/G genotype
Vitamin D Levels. Evidence: 10/10. Source: PMID 20418485. Somewhat Lower.
Vitamin D Deficiency. Evidence: 10/10. Source: PMID 20541252. Increased Risk.
White Blood Cell Count. Evidence: 6/10. Source: PMID 32888494. Slightly Lower.
Neutrophil Count. Evidence: 8/10. Source: PMID 32888494. Slightly Lower.
What this genotype means for the people who carry it
Sample genotype: TT (Homozygous)
Having two copies of the T allele means the body produces highly efficient vitamin D-binding proteins [1]. Large-scale genetic studies show that individuals with this genotype maintain the highest average circulating levels of 25-hydroxyvitamin D [2]. This efficient transport system ensures that bones receive adequate calcium for mineralization, reducing the long-term risk of weakness [1]. Additionally, this genotype is associated with typical white blood cell and neutrophil counts, which are essential components of the innate immune system [3]. Maintaining these baseline levels supports overall metabolic and immune health [2].
Efficient vitamin D transport; Lower risk of deficiency; Typical immune cell counts.
Sample genotype: GG (Homozygous)
Having two copies of the G allele results in less efficient vitamin D-binding protein production and transport [1]. Multiple genome-wide association studies have confirmed that this genotype is one of the strongest genetic risk factors for clinical vitamin D deficiency [2]. Because the transport of vitamin D is compromised, individuals with this genotype often require more dietary intake or sunlight to maintain healthy blood levels [3]. This lower availability can also impact bone health over time if left unmanaged [1]. Furthermore, studies have noted an association between this genotype and lower baseline counts of white blood cells and neutrophils, which are key players in immune defense [4].
Reduced vitamin D transport efficiency; Elevated risk of vitamin D deficiency; Lower baseline white blood cell counts.
Sample genotype: TG (Heterozygous)
Inheriting one G allele alters the binding and transport efficiency of the vitamin D-binding protein [1]. Research indicates that individuals with this genotype tend to have moderately lower circulating levels of 25-hydroxyvitamin D compared to those with the TT genotype [2]. While this does not guarantee a clinical deficiency, it does mean the body may be slightly more sensitive to seasonal drops in sunlight exposure [3]. There is also a minor association with slightly lower baseline white blood cell and neutrophil counts, though usually within normal clinical ranges [4]. Monitoring dietary intake of vitamin D and getting sensible sun exposure can help maintain optimal levels [2].
Moderately reduced vitamin D transport; Slightly higher risk of deficiency; Slightly lower immune cell counts.
Variants with shared genetic architecture
rs4588 · 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 circulating vitamin D levels.
Common genetic determinants of vitamin D insufficiency: a genome-wide association study.
The Polygenic and Monogenic Basis of Blood Traits and Diseases.
Content updated August 2026.
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