Researchers studied 170 people who had COVID-19 to understand if vitamin D levels affect long COVID—the condition where symptoms continue months after infection. They found that people with low vitamin D were nearly six times more likely to develop long COVID symptoms. The study measured vitamin D levels in patients’ blood and tracked their symptoms for at least three months. About 65% of participants developed long COVID, with breathing problems being the most common symptom. The findings suggest that maintaining healthy vitamin D levels through sunlight exposure or supplements might help reduce long COVID risk, though more research is needed to confirm this connection.

The Quick Take

  • What they studied: Whether people with lower vitamin D levels are more likely to develop long COVID symptoms after recovering from the initial COVID-19 infection
  • Who participated: 170 adults aged 18-59 years who had mild COVID-19 confirmed by testing. About half were women and half were men, with an average age of 46 years. Most had received three COVID-19 vaccine doses.
  • Key finding: People with vitamin D deficiency were about 5.8 times more likely to develop long COVID compared to those with adequate vitamin D levels. Those with low vitamin D also experienced more symptoms overall.
  • What it means for you: If you’ve had COVID-19, maintaining healthy vitamin D levels through sunlight exposure, food, or supplements may help reduce your chances of developing long COVID. However, this is one study, so talk to your doctor before making major changes to your vitamin D intake.

The Research Details

Researchers recruited 170 people who had recently recovered from mild COVID-19 and measured their vitamin D blood levels within two months of diagnosis. They then followed these people for at least three months, asking them to report any symptoms that persisted after their initial infection. The study collected information about their age, sex, vaccination status, and vitamin D levels, then compared symptom patterns between people with different vitamin D levels.

The researchers used statistical methods to determine whether vitamin D deficiency was truly connected to long COVID symptoms, even when accounting for other factors like age and vaccination status. This approach helps them understand if vitamin D is genuinely important or if other factors might explain the connection.

This study design is important because it follows people over time and measures vitamin D before symptoms develop, which helps establish a clearer connection between vitamin D and long COVID. By measuring vitamin D levels early and tracking symptoms later, researchers can better understand whether low vitamin D might actually contribute to long COVID rather than just being associated with it.

The study included a reasonable number of participants (170) and followed them for an adequate period (at least 3 months). The researchers measured actual blood vitamin D levels rather than relying on guesses. However, the study only included people with mild initial COVID symptoms, so results may not apply to people who had severe COVID. Additionally, participants self-reported their symptoms, which could introduce some inaccuracy. The study was published in a peer-reviewed journal, meaning other experts reviewed the work before publication.

What the Results Show

About 65% of the 170 participants developed long COVID symptoms. People with vitamin D deficiency (the lowest levels) were nearly six times more likely to have long COVID compared to those with adequate vitamin D levels. On average, people with long COVID had vitamin D levels of 21.52 ng/mL, while those without long COVID had levels of 25.46 ng/mL—a meaningful difference.

When researchers looked at how many symptoms people experienced, those with vitamin D deficiency had significantly more symptoms overall. The most common long COVID symptoms were breathing problems (55% of people), skin issues (51%), and general symptoms like fatigue (39%).

The study found that about 72% of participants had insufficient or deficient vitamin D levels, meaning most people in the study didn’t have enough vitamin D in their blood. Only 28% had adequate levels.

The study found that vitamin D deficiency was particularly associated with experiencing multiple symptoms rather than just one or two. People with low vitamin D tended to report symptoms affecting different body systems—such as both breathing problems and skin issues—rather than isolated symptoms. This suggests vitamin D may influence how the body’s overall recovery process works after COVID-19.

Previous research has suggested that vitamin D plays an important role in immune system function and that low vitamin D is linked to worse outcomes in various infections. This study adds to that evidence by specifically connecting vitamin D deficiency to long COVID development. However, most previous studies on vitamin D and COVID-19 focused on the initial infection severity rather than long-term symptoms, making this research a newer contribution to the field.

This study only included people with mild initial COVID symptoms, so the findings may not apply to people who had severe COVID-19. The study was relatively small (170 people) and only followed people for three months, which is a moderate timeframe. Participants reported their own symptoms rather than having doctors assess them, which could introduce errors. The study doesn’t prove that low vitamin D causes long COVID—only that they’re connected. Additionally, the study didn’t measure other factors that might affect vitamin D levels or long COVID risk, such as diet, sun exposure, or underlying health conditions.

The Bottom Line

Based on this research, maintaining adequate vitamin D levels appears beneficial for reducing long COVID risk (moderate confidence level). Current health guidelines recommend vitamin D levels of at least 20 ng/mL, with optimal levels around 30 ng/mL or higher. You can maintain healthy vitamin D through: (1) regular sun exposure (10-30 minutes several times per week), (2) eating vitamin D-rich foods like fatty fish, egg yolks, and fortified milk, or (3) taking vitamin D supplements if recommended by your doctor. If you’ve had COVID-19, consider asking your doctor to check your vitamin D level.

Anyone recovering from COVID-19 should pay attention to these findings, especially if they’re experiencing persistent symptoms. People at higher risk for vitamin D deficiency—including those with limited sun exposure, darker skin tones, or certain medical conditions—should be particularly attentive. However, people with severe initial COVID-19 should consult their doctor, as this study only included mild cases. Pregnant women, children, and people with certain health conditions should talk to their doctor before starting supplements.

If you’re deficient in vitamin D, it typically takes 4-12 weeks of supplementation or increased sun exposure to raise levels significantly. You might notice improvements in energy and general symptoms within a few weeks, though long COVID symptoms can take months to resolve. It’s important to have realistic expectations—vitamin D alone won’t cure long COVID, but it may help reduce symptom severity and duration.

Want to Apply This Research?

  • Track your vitamin D intake daily (through food, supplements, or estimated sun exposure in minutes) and rate your long COVID symptoms weekly using a 1-10 scale for each symptom type (breathing, energy, skin, etc.). This allows you to monitor whether maintaining adequate vitamin D correlates with symptom improvement over 8-12 weeks.
  • Set a daily reminder to either take a vitamin D supplement (if recommended by your doctor), spend 15-20 minutes in sunlight, or eat a vitamin D-rich food. Log this action in the app to build consistency and track correlation with symptom improvement.
  • Check vitamin D levels with your doctor every 2-3 months if you’re supplementing, and track symptom patterns monthly. Use the app to create a simple chart showing vitamin D intake versus symptom severity over time, which you can share with your healthcare provider to assess whether vitamin D management is helping your long COVID recovery.

This research suggests an association between vitamin D levels and long COVID but does not prove that low vitamin D causes long COVID. Individual results vary significantly. Before starting vitamin D supplements or making major dietary changes, consult with your healthcare provider, especially if you have underlying health conditions, take medications, or are pregnant or nursing. This information is for educational purposes and should not replace professional medical advice. If you’re experiencing severe or worsening long COVID symptoms, seek immediate medical attention.