A 2026 meta-analysis of 10 studies involving 563 familial Mediterranean fever patients found significantly lower vitamin D levels compared to healthy controls, though the difference varied dramatically by season and geography. Winter months showed the largest deficits, and Egyptian patients had lower levels than Turkish patients. Despite low vitamin D, parathyroid hormone and inflammation markers remained similar between groups, suggesting vitamin D deficiency in FMF is complex and individualized.
A new analysis of 10 studies involving 563 patients reveals that people with familial Mediterranean fever (FMF)—a rare genetic condition causing repeated inflammation—tend to have significantly lower vitamin D levels than healthy people. However, the research shows that where you live and what season it is matter a lot. Patients in Egypt had lower vitamin D than those in Turkey, and winter months showed the biggest drops. Interestingly, despite low vitamin D, other inflammation markers didn’t change much. According to Gram Research analysis, this suggests vitamin D deficiency in FMF patients is complex and depends on multiple factors.
Key Statistics
A 2026 meta-analysis of 10 studies including 563 familial Mediterranean fever patients found significantly lower vitamin D levels in FMF patients compared to healthy controls, with seasonal and geographic variations playing major roles in the severity of deficiency.
According to research reviewed by Gram, Egyptian patients with familial Mediterranean fever had noticeably lower vitamin D levels than Turkish patients in the same meta-analysis, demonstrating that geographic location significantly influences vitamin D status.
A 2026 meta-analysis found no significant differences in parathyroid hormone or C-reactive protein levels between familial Mediterranean fever patients and healthy controls despite lower vitamin D, suggesting vitamin D deficiency doesn’t automatically trigger expected hormonal changes.
The 2026 meta-analysis showed that during summer months, vitamin D levels were similar between familial Mediterranean fever patients and healthy individuals, but winter months revealed substantial deficits in the FMF group.
The Quick Take
- What they studied: Whether people with familial Mediterranean fever (a rare inherited condition causing repeated inflammation) have lower vitamin D levels than people without the condition
- Who participated: 563 patients with FMF across 10 different studies, compared to healthy control groups. Patients came from different countries including Egypt and Turkey
- Key finding: FMF patients had significantly lower vitamin D levels overall, but the difference varied greatly depending on season and geographic location. Winter showed the biggest drops, and Egyptian patients had lower levels than Turkish patients
- What it means for you: If you have FMF, your doctor may want to check your vitamin D levels, especially during winter months. However, this doesn’t automatically mean you need supplements—more research is needed to determine the best treatment approach for each person
The Research Details
Researchers looked at 10 previously published studies that compared vitamin D levels in FMF patients versus healthy people without the condition. They followed strict international guidelines (PRISMA) to make sure they selected studies fairly and combined the results using statistical methods that account for differences between studies.
The studies measured vitamin D by checking blood levels of a specific form called 25-hydroxyvitamin D, which is the standard way doctors measure vitamin D status. Researchers also looked at two other markers: parathyroid hormone (PTH), which helps control calcium, and C-reactive protein (CRP), which shows inflammation.
The analysis included studies published through December 2025 from major medical databases. The researchers were careful to include only observational studies that directly compared FMF patients to healthy controls, ensuring they were comparing similar groups.
This approach matters because FMF is rare, so no single study has enough patients to give a clear answer. By combining results from multiple studies, researchers can see patterns that wouldn’t be obvious in smaller studies. However, the studies were quite different from each other, which makes the overall picture less clear—something the researchers acknowledged as a limitation
The research followed international best practices and was registered before completion, which reduces bias. However, the studies included were quite different from each other (high heterogeneity), meaning results varied widely. The researchers rated the certainty of evidence as low, meaning we should be cautious about drawing firm conclusions. More large, well-designed studies are needed to confirm these findings
What the Results Show
The main finding was clear: FMF patients had significantly lower vitamin D levels compared to healthy controls. However, the results varied considerably between studies, with some showing much bigger differences than others.
When researchers looked at seasonal patterns, they found something interesting: during summer months, vitamin D levels were similar between FMF patients and healthy people. This makes sense because sun exposure boosts vitamin D production. The real differences appeared in winter, when everyone’s vitamin D drops, but FMF patients dropped more.
Geographic location also mattered significantly. Patients in Egypt had noticeably lower vitamin D levels than patients in Turkey, likely due to differences in sun exposure, diet, and lifestyle factors between the two countries.
Surprisingly, despite the low vitamin D, the researchers found no significant differences in parathyroid hormone (PTH) or C-reactive protein (CRP) levels between FMF patients and healthy controls. This suggests that while vitamin D is lower, the body’s immediate response to this deficiency and overall inflammation markers weren’t dramatically different.
The analysis revealed that vitamin D deficiency in FMF patients is highly individualized—meaning it depends heavily on personal factors like where someone lives, the time of year, and possibly how severe their FMF symptoms are. This suggests there’s no one-size-fits-all explanation for why FMF patients have lower vitamin D. The high variation between studies indicates that different populations may experience different patterns of vitamin D deficiency
This is the first meta-analysis specifically comparing vitamin D levels between FMF patients and healthy individuals. Previous smaller studies suggested lower vitamin D in FMF patients, but the evidence was mixed and unclear. This analysis confirms the pattern exists but reveals it’s more complicated than initially thought, with seasonal and geographic factors playing major roles. The finding that PTH and CRP don’t significantly differ contradicts some earlier assumptions that vitamin D deficiency would automatically trigger changes in these markers
The biggest limitation is high variability between studies—researchers couldn’t fully explain why results differed so much. The certainty of evidence is low, meaning we shouldn’t treat these findings as definitive. Only 10 studies were included, and some important information was missing from the original studies. The analysis couldn’t determine whether low vitamin D actually causes problems in FMF patients or is just an associated finding. More research from different countries and populations is needed
The Bottom Line
If you have FMF, ask your doctor to check your vitamin D levels, particularly during winter months (moderate confidence). Don’t assume you need supplements without testing—vitamin D needs are individual. If your levels are low, work with your doctor on a treatment plan, which might include supplements, dietary changes, or increased safe sun exposure (moderate confidence). The evidence doesn’t yet support universal supplementation for all FMF patients
People with familial Mediterranean fever should pay attention to these findings, especially those living in northern climates or countries with less sun exposure. Healthcare providers treating FMF patients should consider vitamin D screening as part of routine care. People in sunny climates like Turkey may have less concern than those in less sunny regions. This research is less relevant for people without FMF
If vitamin D is low and you start supplementation, it typically takes 8-12 weeks to see meaningful improvements in blood levels. However, you may not notice physical changes immediately—vitamin D works gradually. Regular testing every 3-6 months helps track whether your levels are improving
Frequently Asked Questions
Do people with familial Mediterranean fever have lower vitamin D levels?
Yes, a 2026 meta-analysis of 563 FMF patients found significantly lower vitamin D levels compared to healthy people. However, the difference depends heavily on season and location—winter shows bigger drops, and geographic region matters significantly.
Should I take vitamin D supplements if I have FMF?
Ask your doctor to test your vitamin D levels first, especially in winter. Don’t assume you need supplements without testing. If levels are low, your doctor can recommend an appropriate treatment plan tailored to your individual needs and location.
Does low vitamin D cause inflammation in familial Mediterranean fever?
Despite lower vitamin D in FMF patients, inflammation markers like C-reactive protein didn’t significantly differ from healthy people in the 2026 meta-analysis. This suggests low vitamin D may not directly trigger the inflammation response in FMF.
Why do FMF patients in Egypt have lower vitamin D than those in Turkey?
Geographic and lifestyle factors influence vitamin D levels, including sun exposure patterns, dietary habits, and cultural practices. The 2026 meta-analysis confirmed Egyptian FMF patients had lower levels, but the exact reasons require further research.
When is the best time to check vitamin D levels if I have FMF?
Winter months show the biggest vitamin D deficits in FMF patients, making it an ideal time for testing. However, regular screening throughout the year helps identify your personal vitamin D patterns and seasonal variations.
Want to Apply This Research?
- Log your vitamin D test results quarterly, noting the season and your location. Track any FMF flare-ups alongside vitamin D levels to see if there’s a personal pattern between vitamin D status and symptom severity
- Set seasonal reminders to discuss vitamin D testing with your doctor, especially before winter. If supplementing, use the app to track daily supplement intake and any changes in how you feel
- Create a long-term chart showing your vitamin D levels across seasons and years. Note any changes in FMF symptoms, sun exposure, diet, and location to identify your personal vitamin D patterns
This research summary is for educational purposes and should not replace professional medical advice. If you have familial Mediterranean fever or suspect you do, consult with a rheumatologist or qualified healthcare provider before starting any vitamin D supplementation or making changes to your treatment plan. The findings presented here show associations and patterns but do not establish causation. Individual vitamin D needs vary based on location, season, genetics, and overall health status. Always have your vitamin D levels tested by a healthcare provider before supplementing.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.