A blood test reports vitamin D or B12 as a single number, and treats a low one as diet or sun exposure. Genetics moves that number too — mostly through how the body transports and converts a nutrient, not through how much of it someone eats.
Why this topic Vitamin D testing has become routine and over-the-counter genetic tests now advertise "nutrient absorption" reports, which mostly rest on a handful of the same common variants covered here.
Solid lines are connections this site curates. Dashed lines mean the two ends share a research paper — worth knowing, and not a claim that one explains the other.
Counted in Europe PMC, where the title or abstract names both this topic and that rsID. The number is papers, not evidence of a cause.
GC
Vitamin D levels
87 papers →MTHFR
Folate metabolism (MTHFR C677T)
27 papers →MTHFR
Folate metabolism (MTHFR A1298C)
12 papers →NADSYN1
Vitamin D levels
11 papers →GC
Vitamin D levels
4 papers →DHCR7
Systemic lupus erythematosus
4 papers →IL29
Chronic hepatitis C infection
4 papers →FTO
Menarche (age at onset)
4 papers →FUT2
Pediatric autoimmune diseases
3 papers →ALDH2
Alcohol flush reaction
3 papers →PDE3B
Vitamin D levels
2 papers →SCARB1
Vitamin E levels
2 papers →TGFB1
Colorectal cancer
2 papers →ESR1
Bone mineral density (spine)
2 papers →FUT2
Secretor status
2 papers →ZNF259
Triglyceride levels
2 papers →CF1
Age-related macular degeneration (choroidal neovascularisation)
1 paper →CYP2R1
Vitamin D levels
1 paper →ESR1
Bone mineral density (hip)
1 paper →HMGA2
Head circumference (infant)
1 paper →IRF4
Freckling & sun sensitivity
1 paper →APOA5
Carotenoid and tocopherol levels
1 paper →HERC2 / OCA2
Eye color
1 paper →ESR1
Breast cancer
1 paper →AGER
Pulmonary function
1 paper →CCR5
HIV-1 resistance (CCR5-delta32)
1 paper →LRP5
Bone mineral density
1 paper →NRTN
N-glycan levels
1 paper →SLCO1B1
Statin muscle-side-effect risk
1 paper →ARID5B
Acute lymphoblastic leukemia (childhood)
1 paper →RAP1A
Osteoporosis-related phenotypes
1 paper →SLC4A7
Breast cancer
1 paper →MCM6 / LCT
Lactose tolerance
1 paper →BDNF
Smoking behavior
1 paper →APOE
Cholesterol, total
1 paper →CYP1A2
Caffeine metabolism
1 paper →UGT1A1
Bilirubin levels
1 paper →FTO
Obesity-related traits
1 paper →Europe PMC, title and abstract only, searched for “vitamin d levels”, “vitamin d insufficiency”, “25-hydroxyvitamin d”, “vitamin b12 levels”, “folate levels”, “vitamin e levels” alongside each published rsID. Full text was not counted: it returns every paper with an rsID buried in a supplementary table. Recounted monthly.