Why Standard Vitamin D Dosing Isn’t Right For Everyone
Up to 40–50% of people worldwide have low vitamin D levels. That includes people living in sunny climates and people who take supplements consistently.
If your vitamin D levels stay low despite doing everything “right,” it’s easy to assume you’re missing something obvious. More often, the issue isn’t effort, consistency, or knowledge. It’s biology.
Research now shows that genetic differences influence how your body makes, converts, transports, and responds to vitamin D. For some people, standard recommendations simply aren’t enough to produce the same blood levels, or the same benefits, as they do for others.
That’s why one person can maintain healthy vitamin D levels with minimal effort, while someone else struggles despite sun exposure and supplements. It’s not a failure. It’s information.
Vitamin D: A Vitamin, Or A Hormone?
Vitamin D is often treated like a simple nutrient: get some sun, take a supplement, move on.
Actually, vitamin D behaves more like a hormone. It influences hundreds of genes throughout the body and plays a role in far more than bone health. Immune function, mood regulation, muscle strength, and cardiovascular health are all influenced by vitamin D status.
When vitamin D is low, symptoms don’t always show up as something obvious or dramatic. Fatigue, frequent infections, low mood, muscle aches, or slow recovery can all be part of the picture. This is one reason vitamin D issues are easy to overlook or oversimplify.
How Your Body Produces and Uses Vitamin D
Vitamin D comes from three main sources:
- Sun exposure
- Food (a relatively small contributor)
- Supplements (often necessary in northern climates like Canada
But vitamin D isn’t active the moment it enters your body. It has to move through several steps before it can be used.
At a high level, vitamin D must:
- Be produced in the skin or absorbed from food or supplements
- Be converted in the liver into a storage form (the one measured on blood tests)
- Be activated and delivered to tissues so cells can respond
If there’s a slowdown at any point along that pathway, vitamin D levels or its effectiveness can be lower than expected.
Where Gene Mutations Can Interfere With Vitamin D Production
This is where genetics come in. Certain genes influence how efficiently vitamin D moves through that process.
Three commonly studied gene mutations include:
GC (transport) – This gene affects vitamin D binding protein, which carries vitamin D through the bloodstream. If transport is less efficient, higher intake may be needed to deliver the same amount to tissues.
CYP2R1 (conversion) – This gene helps convert vitamin D into its storage form. Variants here can result in lower blood levels even with regular supplementation.
VDR (cellular response) – This gene affects how well your cells respond to vitamin D. Some people need higher blood levels to experience benefits like improved energy, immunity, or mood.
Other genes can also play a role, but the takeaway here is that genetics can create bottlenecks at multiple stages and that helps explain why generic dosing doesn’t work for everyone.
Signs Your Genes May Be Contributing To Your Vitamin D Deficiency
Genetics may be worth considering if you notice patterns like:
- Continued low vitamin D despite supplements
- Minimal improvement in symptoms even when blood levels rise
- Frequent infections or slow recovery
- Fatigue that doesn’t improve with rest
- Seasonal low mood year after year
- Muscle aches, bone pain, or low bone density
Family history can offer clues too. If close relatives have struggled with vitamin D deficiency, osteoporosis, autoimmune conditions, or seasonal mood issues, shared genetic factors may be involved.
This isn’t about self-diagnosing. It’s about recognizing when standard advice isn’t enough.
Testing Your Vitamin D Levels: Blood and Gene Testing
Blood testing comes first
The 25-hydroxyvitamin D blood test is the foundation and it shows how much vitamin D your body is storing.
Most labs consider levels above 50 nmol/L sufficient. However, many clinicians aim higher, often in the 100–150 nmol/L range, especially when symptoms continue. The right target depends on the individual and the context, not just the lab range.
Genetic testing adds context
Genetic testing doesn’t replace bloodwork. It helps explain why vitamin D levels may be difficult to raise or why benefits aren’t showing up as expected.
At Sage, genetic testing through DNALabs looks at variations related to vitamin D metabolism and presents results in clear, non-technical categories. It’s like a roadmap, not a prescription.
Critical Nutrients for Vitamin D Synthesis
Vitamin D doesn’t act alone. Several nutrients influence how well it works:
- Magnesium, which supports vitamin D activation
- Vitamin K2, which helps guide calcium to bone rather than soft tissue
- Dietary fat, which improves absorption of this fat-soluble vitamin
So, in addition to genetics, if these nutrients are deficient, even high vitamin D doses may not help with symptoms.
How Much Vitamin D Is Safe To Take?
Vitamin D is generally safe when used appropriately, but more isn’t always better. For most adults, upper intake limits are commonly set around 4,000 IU per day, though individual needs vary.
Professional guidance is especially important if:
- You have multiple genetic risk factors
- You have kidney or cardiovascular conditions
- Supplements haven’t helped after several months
- You experience symptoms like nausea, fatigue, or kidney stones
Monitoring may include vitamin D, calcium, parathyroid hormone, and kidney markers to ensure safety and effectiveness.
If I Have Genetic Mutations, Am I Always Going to Have A Vitamin D Deficiency?
Your genes aren’t your destiny. They simply help explain why generic advice may not have worked for you in the past.
Once you understand how your body handles vitamin D, you can stop guessing and focus on a strategy that fits your body and your life. Many people with genetic challenges improve their vitamin D status once their plan is properly tailored.
Optimize Your VItamin D Levels With A Personalized Nutrition Plan
Contact our clinic to explore genetic testing and create a plan tailored to your unique blueprint. Together, we can finally address the genetic factors that may be holding you back and help you feel your best again.
Work with nutritionist Renee O’Shea to get genetic testing and optimize your vitamin D levels with nutrition and supplementation.
Book a discovery call with Renee today!
References
- Roman Martínez, M., et al. (2025). “Nutri-Epigenetic Regulation of Vitamin D, Impact on Metabolism and Epigenetics.” Nutrients, 17(13), 4876. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12299634/
- Rajendran, A., et al. (2025). “SDR42E1 Modulates Vitamin D Absorption and Cancer Pathogenesis.” Frontiers in Endocrinology, 16, 1585859. https://www.frontiersin.org/journals/endocrinology/articles/10.3389/fendo.2025.1585859/
- Urszula, M., et al. (2024). “The Power of Vitamin D: Is the Future in Precision Nutrition through Nutrigenomics and Nutri-Epigenetics?” Nutrients. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11054101/
- Pike, J. W., et al. (2024). “Consensus Statement on Vitamin D Status Assessment and Interpretation.” Endocrine Reviews, 45(5), 625-671.
https://academic.oup.com/edrv/article/45/5/625/7659127 - Deepika, et al. (2025). “Vitamin D: Recent Advances, Associated Factors, and Its Role.” Nature Food Science, 6, 678-684. https://www.nature.com/articles/s41538-025-00460-5
- Gralak, M. A., et al. (2025). “Genetic Variants in Vitamin D Metabolism-Related Genes Are Associated with Serum 25(OH)D Levels.” Journal of Steroid Biochemistry and Molecular Biology. https://www.sciencedirect.com/science/article/abs/pii/S02715317250003147.
- Nascimento, M. B., et al. (2024). “Vitamin D Supplementation and Type 1 Diabetes: Systematic Review of Randomized Controlled Trials.” Nutrients.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11054101/ - Voltan, G., et al. (2023). “Vitamin D: An Overview of Gene Regulation, Ranging from Physiology to Disease.” International Journal of Molecular Sciences, 24(17), 8990. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10531002
- Nissen, J., et al. (2014). “Common Variants in CYP2R1 and GC Genes Predict Vitamin D Levels in Healthy Adults.” PLOS ONE. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.008990710.
- National Institutes of Health Office of Dietary Supplements. (2025). “Vitamin D – Health Professional Fact Sheet.” https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
Renee O’Shea, Registered Nutritionist
Sage Naturopathic Clinic