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Last reviewed: May 12, 2026 Last updated: May 12, 2026

Written by: Jay Hastings , CEO of PlexusDx

Jay Hastings is the CEO of PlexusDx, a precision health company focused on genetic testing, blood biomarker insights, and personalized wellness recommendations. He has more than 20 years of experience across healthcare innovation, genomics, laboratory operations, healthcare investing, and strategic finance. His work has included scaling healthcare startups, leading CLIA lab integrations, and helping expand consumer access to precision health tools.

Medically reviewed by: Jayden Lee, PharmD, EMBA

Jayden Lee, PharmD, EMBA, is the PlexusDx Medical Science Liaison with a PharmD and MBA specializing in pharmacogenomics and clinical product development, with a proven ability to bridge the gap between genomic research and practical patient outcomes. Dr. Lee has more than 10 years of professional experience in clinical pharmacy, academia, and research.

How Your GC Gene Affects Vitamin D: What the rs1155563 Genotype Means for You

Vitamin D plays an important role in bone health, immune function, muscle strength, and nerve activity. Your body gets vitamin D from sunlight, certain foods, and supplements. A protein called Vitamin D Binding Protein, made by the GC gene, carries vitamin D through your bloodstream to the tissues that need it. Variations in the GC gene can change how well that protein works and influence blood vitamin D levels.

This article explains the rs1155563 variant in the GC gene and what different genotypes may mean for your vitamin D status. You will find practical, easy to follow diet, supplement, and lifestyle suggestions and guidance on when to consider testing. PlexusDx does not provide medical advice. Always consult your healthcare provider before making changes to supplements, medications, or your treatment plan.

Why the GC Gene Matters

Vitamin D circulates in the blood bound to Vitamin D Binding Protein, or DBP. DBP transports vitamin D from the skin and food to organs like the liver and kidneys, where it is converted into the active form your body uses. The rs1155563 variant in the GC gene affects DBP structure or levels and can change how much vitamin D stays available in circulation. That can influence the amount detected on a standard blood test and how much ends up inside cells.

What You Can Do to Support Healthy Vitamin D Levels

  • Test first when possible: Ask your healthcare provider about a 25-hydroxyvitamin D blood test. This is the standard measure of vitamin D status and helps guide whether you need extra vitamin D.
  • Eat vitamin D rich foods: Include fatty fish like salmon, mackerel, and sardines; egg yolks; and vitamin D fortified foods such as milk, plant milks, and some cereals.
  • Safe sun exposure: Brief, regular sun exposure to uncovered skin can boost vitamin D production. Time depends on skin tone, location, season, and sunscreen use. Balance sun exposure with skin cancer risk and follow guidance from your healthcare provider.
  • Consider supplementation when appropriate: If testing shows low levels or if sun exposure and diet are limited, vitamin D supplements are a reliable option. Work with your healthcare provider to pick a dose and form that fits your needs.
  • Monitor and adjust: If you start supplements, recheck vitamin D status after a few months to confirm dosing is adequate and safe.
  • Supportive nutrients: Maintain adequate calcium, magnesium, and vitamin K intake to support bone and muscle health while you optimize vitamin D.

When to Talk to Your Healthcare Provider

  • If you have symptoms that might relate to low vitamin D such as unexplained muscle weakness, frequent infections, bone pain, or fatigue
  • If you have limited sun exposure due to geographic location, dress practices, or mobility limitations
  • If you have conditions that affect fat absorption like celiac disease or inflammatory bowel disease
  • If you are pregnant, breastfeeding, elderly, or taking medications that interfere with vitamin D metabolism
  • If you are considering high dose vitamin D supplementation or vitamin D injections
2 effect alleles (CC) — Higher risk of lower vitamin D

If your genotype is CC for rs1155563, you carry two copies of the effect allele. This version of the GC gene is associated with lower circulating vitamin D levels. The Vitamin D Binding Protein produced may bind or circulate differently, which can reduce the amount of vitamin D measured in blood tests and possibly the vitamin D available to tissues.

Recommended actions

  • Ask your healthcare provider for a 25-hydroxyvitamin D blood test to confirm your vitamin D status.
  • Increase dietary sources of vitamin D: aim for fatty fish 2 to 3 times per week, include egg yolks and fortified foods.
  • Discuss vitamin D supplementation with your provider. People with two effect alleles may need higher supplemental doses to reach optimal blood levels, but dosing should be personalized and monitored with testing.
  • Get safe sun exposure when possible. Even with sun exposure, supplementation and testing are valuable because GC variation can affect circulating levels.
  • Recheck vitamin D levels after 8 to 12 weeks of supplementation or lifestyle changes to ensure improvement and safety.
1 effect allele (CT) — Likely lower vitamin D

If your genotype is CT for rs1155563, you carry one copy of the effect allele. This genotype is associated with a likely reduction in circulating vitamin D compared to people without the effect allele. The Vitamin D Binding Protein may function slightly differently, which can influence how much vitamin D is available in the bloodstream.

Recommended actions

  • Consider a 25-hydroxyvitamin D test to determine your baseline.
  • Enhance dietary intake of vitamin D through fatty fish, fortified milk or plant milks, and eggs.
  • Talk with your healthcare provider about moderate supplementation if your test shows low or borderline levels. A personalized dose based on testing is the safest approach.
  • Use sun exposure safely to support vitamin D production while balancing skin protection.
  • Follow up with testing after a few months if you make changes so your provider can adjust dosing as needed.
0 effect alleles (TT) — Typical vitamin D transport

If your genotype is TT for rs1155563, you carry two copies of the non-effect allele. This genotype is associated with typical Vitamin D Binding Protein function and usual circulating vitamin D levels when diet and sun exposure are adequate.

Recommended actions

  • Maintain a balanced approach: eat vitamin D rich foods, get safe sun exposure, and consider periodic testing especially during winter months or if you have risk factors for deficiency.
  • Supplement if testing shows low levels or if you have limited sun and dietary sources. Work with your healthcare provider to pick an appropriate dose.
  • Continue routine health maintenance including bone health and screening as recommended by your provider.

Practical Supplement Guidance

  • Forms: Vitamin D3 is commonly recommended for raising blood levels. Your provider will advise whether D2 or D3 is best for you.
  • Dosing: Typical maintenance doses range from 600 to 2000 IU daily for many adults, but higher doses may be used short term under medical supervision to correct deficiency.
  • Monitoring: A follow up 25-hydroxyvitamin D test after 8 to 12 weeks of supplementation helps confirm that levels are improving and not exceeding safe ranges.

Final Notes

Your rs1155563 genotype offers helpful information about how your body may transport and maintain vitamin D, but genetics is one piece of the picture. Lifestyle, diet, sun exposure, body composition, medications, and medical conditions also shape vitamin D status. Testing and working with your healthcare provider are the best ways to create a safe, effective plan tailored to your needs.

PlexusDx does not provide medical advice. This information is educational and not a substitute for professional medical evaluation. Always consult your healthcare provider before starting or changing supplements, medications, or treatment plans.

If this genetic variant is present in your PlexusDx results, the following tests and reports are commonly used to explore it further:

🧬 Genetic Tests:

🧪 Blood Tests:

📄 Genetic Report:

Frequently Asked Questions About Vitamin D and GC rs1155563

What does the GC rs1155563 genotype mean for my vitamin D levels?

The GC gene helps produce Vitamin D Binding Protein (DBP), which carries vitamin D through your bloodstream to tissues that need it. The rs1155563 variant can influence DBP structure or levels, which may change how much vitamin D is detected on a standard blood test and how much becomes available to cells. In the guidance provided, CC (2 effect alleles) is associated with a higher risk of lower vitamin D, CT (1 effect allele) is likely lower, and TT (0 effect alleles) is associated with typical vitamin D transport when diet and sun exposure are adequate.

How do I check whether I should supplement vitamin D with the rs1155563 variant?

Ask your healthcare provider about a 25-hydroxyvitamin D blood test, which is the standard measure of vitamin D status and helps guide next steps. If your genotype is CC or CT, testing is especially useful because the GC variation may shift circulating vitamin D levels. If you start vitamin D, recheck vitamin D after about 8 to 12 weeks to confirm dosing is effective and staying within safe ranges.

What lifestyle and diet strategies can help support vitamin D regardless of rs1155563 genotype?

You can support vitamin D through multiple “stackable” habits: eat vitamin D-rich foods (fatty fish like salmon/sardines/mackerel, egg yolks, and fortified foods), use safe sun exposure when possible, and consider supplementation if testing shows low or borderline levels or if sun and diet are limited. Additional nutrients like calcium, magnesium, and vitamin K can support bone and muscle health while you optimize vitamin D. For supplementation decisions—especially higher doses—work with your healthcare provider to choose a personalized dose based on test results.

What tests can help me learn more about Vitamin D and GC rs1155563?

The Optimal Diet and Weight Loss Genetic Test delivers over 295 genetic insights related to nutrition response, body composition, metabolism, and fitness. The Diet and Nutrition Genetic Report translates your results into personalized, actionable guidance. Your healthcare provider can also recommend targeted blood tests based on your specific pathway results and health history to complement your genetic insights with current biomarker data.

Medical and Editorial Standards

Medical review process: This article was reviewed for medical accuracy, scientific clarity, evidence alignment, and appropriate discussion of genetics, medications, supplements, biomarkers, and health-related claims.

Sources and evidence: PlexusDx educational content is developed using peer-reviewed research, clinical literature, reputable medical references, and, where applicable, public health or regulatory guidance. References are included at the end of the article when scientific, medical, or health-related claims are discussed.

Commercial transparency: PlexusDx offers genetic testing, blood biomarker testing, personalized supplement recommendations, and related precision wellness services. Product mentions are intended to help readers understand available options and should not be interpreted as medical advice.

Important disclaimer: PlexusDx educational content is for informational purposes only and should not be used as a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making decisions about medications, supplements, genetic testing, lab testing, or health-related care.