Researchers studied 60 people to understand why some individuals struggle with vitamin D deficiency even when taking supplements. They discovered that certain genetic variations—differences in your DNA—can affect how your body processes and uses vitamin D. The study found that people with specific genetic patterns were more likely to have allergies, thyroid problems, or autism. This research suggests that a one-size-fits-all approach to vitamin D supplementation may not work for everyone, and doctors might need to consider your unique genetic makeup when recommending vitamin D treatment.

The Quick Take

  • What they studied: How differences in your genes affect your body’s ability to use vitamin D, and whether these genetic differences connect to allergies, thyroid disease, and autism
  • Who participated: 60 people (44 women and 16 men) living in Turkey who had genetic testing done and either had allergies, autism, or thyroid problems
  • Key finding: People with certain genetic variations were more likely to have low vitamin D levels and to have allergies, thyroid disease, or autism. Different genetic patterns appeared in each condition—for example, one type of genetic variation was more common in people with autism, while different variations were more common in people with allergies.
  • What it means for you: If you have low vitamin D levels that don’t improve with regular supplements, your genes might be playing a role. This suggests doctors may eventually be able to test your genes to create a personalized vitamin D plan just for you. However, this research is still early, and more studies are needed before this becomes standard medical practice.

The Research Details

This was a retrospective study, which means researchers looked back at information that had already been collected. They examined genetic test results from 60 people who visited a clinic in Istanbul, Turkey between 2022 and 2024. All participants had already been tested for three specific genes that affect how the body handles vitamin D: CYP2R1, GC, and VDR. The researchers compared the genetic results of people with allergies, autism, or thyroid disease to see if certain genetic patterns appeared more often in each group.

The study focused on finding genetic variations—small differences in DNA that are common in the population. Think of it like different versions of an instruction manual: everyone has the same basic manual, but some people have slightly different versions that might change how their body works. The researchers looked at whether people with certain genetic variations were more likely to have vitamin D problems and related health conditions.

Understanding the genetic side of vitamin D deficiency is important because millions of people take vitamin D supplements without getting better. If we can identify which genetic variations make it harder for your body to use vitamin D, doctors could eventually test for these variations and create personalized treatment plans. This approach, called nutrigenomics or personalized nutrition, could help people get better results from their vitamin D treatment.

This study has some important limitations to understand. It’s relatively small (60 people) and only looked at people who already had health problems and had chosen to get genetic testing. The study didn’t include a control group of healthy people for comparison, which makes it harder to know if these genetic variations are truly the cause of the health problems or just happen to appear together. The research was descriptive rather than experimental, meaning it observed patterns but didn’t test whether changing vitamin D levels would actually improve the health conditions. More research with larger groups and different study designs is needed to confirm these findings.

What the Results Show

The researchers found that three specific genes involved in vitamin D processing showed variations more frequently in people with allergies, autism, or thyroid disease compared to what would be expected in the general population. The VDR gene had the most variations, with different types of variations appearing in different conditions.

For people with thyroid disease (Hashimoto’s thyroiditis), three specific VDR variations were more common: FokI, ApaI, and BsmI. For people with autism, the TaqI variation was more frequently observed. For people with allergies, all four VDR variations (BsmI, FokI, ApaI, and TaqI) appeared at higher rates.

The researchers also noted that these genetic variations might affect not just how your body processes vitamin D, but also the balance of bacteria in your gut. Your gut bacteria play an important role in your immune system and overall health, so changes to these bacteria could contribute to allergies, thyroid problems, and autism.

Beyond the main genetic findings, the study highlighted the connection between vitamin D metabolism and gut health. The researchers suggested that genetic variations affecting vitamin D processing might also change how diverse and healthy your gut bacteria population is. This is significant because your gut bacteria influence your immune system, which in turn affects allergies and autoimmune conditions like thyroid disease. The study also emphasized that vitamin D deficiency is surprisingly common worldwide, even in countries with plenty of sunshine and despite widespread supplementation efforts, suggesting that genetic factors may explain why some people remain deficient.

This research builds on earlier studies showing that vitamin D deficiency is linked to allergies, thyroid disease, and autism. However, most previous research focused on vitamin D levels themselves rather than the genetic reasons why some people can’t maintain healthy vitamin D levels. This study adds a new piece to the puzzle by suggesting that your genes may be a major reason why you might struggle with vitamin D deficiency. The findings align with the growing field of nutrigenomics, which studies how your genes affect your nutrition and health.

This study has several important limitations. First, it’s small—only 60 people—so the findings might not apply to larger populations. Second, all participants already had health problems and had chosen genetic testing, which means the results might not represent people without these conditions. Third, the study didn’t include a comparison group of healthy people, making it impossible to know if these genetic variations are actually causing the health problems or just appearing together by chance. Fourth, the study was observational, meaning researchers only looked at patterns without testing whether changing vitamin D levels would actually improve the conditions. Finally, the study didn’t measure actual vitamin D levels in the blood, so we don’t know exactly how deficient each person was.

The Bottom Line

Based on this research, here are evidence-based recommendations with appropriate caution: If you have persistent low vitamin D levels despite supplementation, ask your doctor about genetic testing for vitamin D metabolism genes. This is a moderate confidence recommendation because the research is promising but still early. Continue taking vitamin D as recommended by your doctor—don’t stop based on this study alone. If you have allergies, thyroid disease, or autism and also have low vitamin D, mention both to your doctor so they can consider the genetic connection. This is a low-to-moderate confidence recommendation because more research is needed. Don’t assume you have a genetic variation without testing—many people with these conditions don’t have the variations found in this study.

This research is most relevant for people who have low vitamin D levels that don’t improve with standard supplementation, especially if they also have allergies, thyroid disease, or autism. It’s also important for people with a family history of these conditions. Healthcare providers, particularly those interested in personalized medicine and nutrigenomics, should pay attention to these findings. People without these conditions or without vitamin D deficiency don’t need to change anything based on this research. This study is not yet ready to change standard medical practice, but it points toward future personalized approaches.

If you were to get genetic testing and adjust your vitamin D treatment based on the results, you might expect to see improvements in vitamin D blood levels within 2-3 months, similar to standard vitamin D supplementation. However, improvements in allergies, thyroid function, or autism symptoms would likely take longer—typically 3-6 months or more—because these conditions are complex and involve many factors beyond vitamin D. Be patient and work closely with your healthcare provider to monitor progress.

Want to Apply This Research?

  • Track your vitamin D blood levels every 3 months (or as recommended by your doctor) and log them in the app along with your supplement dose and type. Also track any changes in allergy symptoms, energy levels, or other health markers to see if optimized vitamin D treatment helps.
  • If you have low vitamin D and suspect a genetic component, use the app to set a reminder to discuss genetic testing with your doctor at your next appointment. Set daily reminders for taking your vitamin D supplement at the same time each day, and log which type and dose you’re taking so you can discuss personalized options with your healthcare provider.
  • Create a long-term tracking system in the app that records: (1) vitamin D supplement type, dose, and timing; (2) vitamin D blood test results with dates; (3) symptoms related to allergies, energy, mood, or other health concerns; (4) any genetic test results once obtained. Review this data every 3 months with your healthcare provider to assess whether your current vitamin D approach is working and whether genetic testing might be helpful.

This research is preliminary and should not replace medical advice from your healthcare provider. The study was small and observational, meaning it identified patterns but didn’t prove cause-and-effect relationships. Genetic testing for vitamin D metabolism is not yet standard medical practice and may not be covered by insurance. Do not change your vitamin D supplementation or stop taking supplements based on this study alone. If you have concerns about vitamin D deficiency, allergies, thyroid disease, or autism, consult with your doctor or a registered dietitian who can evaluate your individual situation, order appropriate blood tests, and recommend personalized treatment. This research suggests future possibilities for personalized vitamin D treatment but is not yet ready for widespread clinical application.